1 TITLE “Clinical and Scientific Aspect of Inlay Fixed Partial Dentures”

UNIVERSITY OF SIENA SCHOOL OF DENTAL MEDICINE

PHD PROGRAM: “DENTAL MATERIALS AND CLINICAL APPLICATIONS”

Ph D THESIS OF: Carlo Monaco

TITLE “Clinical and scientific aspect of Inlay Fixed Partial Dentures”

ACCADEMIC YEAR 2004/2005

December 2005 Siena Italy

Committee: Promoter Prof. Marco Ferrari Co-Promoter Prof. R. Scotti Prof. xxxxxxxxxxxx Prof. xxxxxxxxxxxx Prof. xxxxxxxxxxxx Prof. xxxxxxxxxxxx

TITLE

“Clinical and scientific aspect of Inlay Fixed Partial Dentures” ______

CANDIDATE

Carlo Monaco

December 2005

2 CONTENTS

Chapter 1: General introduction 1.1 Tooth structure removal associated with various preparation designs 1.2 Metal-free inlay retainer restorations 1.3 Indication and contraindications of inlay-fixed partial denture

Chapter 2: The use of fiber reinforced composites in dentistry 2.1 Fiber-reinforced composite systems 2.2 Properties of the fibers and polymer matrices 2.3 Impregnation of the fibers 2.4 Quantity of fibers 2.5 Direction of the fibers 2.6 Position of fibers 2.7 Water sorption of FRC matrix

Chapter 3: Marginal adaptation of IFPDs 3.1 Marginal adaptation of three partial bridges made with different structure material.

Chapter 4: Criteria for selecting the materials for IFPDs 4.1 Fracture strength of three partial bridges made with different structure material.

Chapter 5: laboratory process for high volume fiber framework 5.1 Fiber reinforced composite with a high volume framework: a technical procedure.

Chapter 6: Different structure of the framework 6.1 Clinical Evaluation of Fiber-Reinforced Composite IFPDs.

Chapter 7: adhesive procedures 7.1 Inlay Bridge With a New Microfilled Composite: A Clinical Report

Chapter 8: Clinical trial 8.1 Randomized controlled trial of Fiber-Reinforced Composite Inlay Fixed Partial Dentures: two-year results.

Chapter 9: Alternative materials as regards FRC 9.1 Fatigue test in shear: its effect on bond of a glass-infiltrated alumina ceramic to human dentin, using different luting procedures.

Chapter 10 Other clinical application of FRC 11.1 Clinical evaluation of teeth restored with quartz fiber-reinforced epoxy resin posts.

Chapter 11 Conclusions Summary

4 Chapter 1 General Introduction

When missing tooth structure or teeth are replaced, minimal biologic risk should be involved to reestablish function and esthetics. To proven reliability and durability of complete-crown metal ceramics made them the method of choice for posterior single- tooth restorations and fixed partial denture (FPD). However, this restoration required considerable reduction of tooth structure. The increased use of the adhesive technique and preservation of dental tissues have greatly impacted conservative tooth preparation design. The development of fibre-reinforced composite (FRC) technology and all-ceramic systems has opened the potential for fabrication of metal- free restorations with durability and good aesthetics. This thesis contains a study on several different basic and clinical aspects related to the use of inlay-fixed partial dentures made with fiber-reinforced composites and all ceramic systems. Starting from the assessment of the differences between the amount of tooth structure removed for conventional preparation and various innovative designs for fixed prosthodontics, the next step was to analyse the different materials that can be used when missing tooth must be replaced. Inlay-fixed partial dentures and dental implants are the true alternatives to the conventional metal-ceramic three-unit bridges; for these reason an overview regarding the properties advantages and disadvantages of fiber-reinforced materials is presented. As actually different fiber- reinforced composites are available on the market, it is important for the clinician to know the properties of each system to select the more appropriate for the specific clinical application. The first objective of this thesis was to evaluate before and after fatigue the marginal adaptation of inlay fixed partial dentures made with different materials and establish a connection between the quality of continuous/non-continuous margins and the mechanical properties of different materials. The second was indeed to conduct a study to assess the fracture strength and the dye penetration after fatigue of one fiber- reinforced composite and two all-ceramic systems, and to verify the existence of a correlation between the mechanical resistance and the microleakage. Another goal of this thesis was in fact to evaluate if and how different methods of positioning of the

5 fibers for the framework can increase the fracture strength and reduced the flexibility of the bridges. The design of the fiber framework is an important prerequisite to obtain a durable clinical success when using fiber-reinforced composite. Another step of this thesis was to describe the technical procedure to obtain a framework with a high volume of fiber; for these reason a clinical study comparing the survival rate of inlay fixed partial dentures made with different framework design is presented. Bonding procedures represent the goal for the term of partial restorations. The next step of this thesis was to describe the luting procedures and the surface treatment for the inlay bridges and to compare the clinical performances and the post-operative sensibility of three- and two-step adhesive systems after two-year observation period. Alternative materials to the metal-ceramic restorations went through rapid developments in the last few years, in particular alumina- and zirconia based ceramics. Both these materials represent the future alternatives of the fiber-reinforced composite but their clinical applications in partial restorations are still limited. The next steps of this thesis were the analysis of the bond of a glass-infiltrated alumina ceramic to human dentin, using different luting procedures. Finally the use of fiber-reinforced composite in the reconstruction of the endodontically treated teeth is examined with according to the aim of the minimal intervention philosophy.

1.1 Tooth structure removal associated with various preparation designs

The introduction of more invasive complete crown preparation for metal- and all- ceramic crowns has been correlated with an increase in pulpal complications since these restorations require considerable reduction of tooth structure (Creugers et al 1994). For a metal-ceramic shoulder preparation, a facial tooth reduction of about 1.3 to 1.5 mm and an occlusal reduction of 2.0 mm are recommended (McLean JW 1980, Rosenstiel et al 1995). In 1966, only 0.4% to 2% radiographic periapical pathologies were found (Ericsson et al 1966), whereas in 1970, 2.9% was reported (Schwartz et al 1970), and about 10 years later up to 4.0% periapical pathologies were detected (Kerschbaum et at 1981). These results are explained by the use of air turbines () and more invasive shoulder or chamfer preparations compared to the feather-edge design

6 used in the 1960s and 1970s (Klötzer 1984). A lower number of endodontic complications are associated with less invasive preparations. In a literature review, inlay restorations at 10 years showed a lower rate of loss of pulpal vitality (5.5%) compared to complete crowns (14.5%) (Kerschbaum et al 1981). The mechanical reliability and broad range of indications have made complete crowns the preferred denture retainer. However, wing—shaped retainers with retentive elements such as grooves made of metal have demonstrated a remarkable long-term success rate if the clinical protocol is followed carefully (Creugers et al 1992). The gravimetric analysis (Edelhoff et al 2002) showed that for a metal-ceramic crown retainer preparation, almost eight times more tooth structure must be removed compared to an adhesive wing-and groove attachment for a resin-bonded cast-metal fixed partial denture. The “new” half-crown preparation assigned for all ceramic fixed partial dentures (FPDs) required a similar amount of tooth structure removal as the onlay and cost approximately half of the tooth structure of a complete crown design. The percentage of tooth structure removal associated with the different preparation designs for a mandibular premolar was 19.3% for mesial/distal occlusal inlay without transverse ridge or central groove, 30.4% for mesial/distal occlusal inlay with transverse ridge or central groove and 75.9% for mete-ceramic complete crown. Similar percentages of tooth structure removal were found for the same kind of preparation in mandibular molar (19.3%, 25.5%, 73.1%). The inclusion of enamel promotes a superior bond over dentin, lower post- cementation sensitivity, improved support of the materials used for the restorations, and reduced endodontic intervention. The positive influence of tooth structure preservation on the life expectancy of the pulp was reported in the literature. For cast-metal resin- bonded FPDs, a 0.13% rate of loss of pulpal vitality up to 5 years was reported, compared to 9.1% for complete crown abutments in the same period (Paszyna et al 1990).

1.2 Metal-free inlay retainer restorations For the past 30 yr, some dentists have avoided the use of full coverage retainers for fixed partial dentures in order to conserve sound tooth substance. Generally, metal- reinforced systems are the materials of choice for fabricating posterior fixed partial dentures because of their reliability and durability. Inlay-retained FPDs made of

7 metal alloys are been usually seated using the conventional cementation technique and cements (Kopp 1970). Before adhesive techniques were introduced to restorative dentistry, conventionally cemented partial crowns or inlays, made of cast gold, were used instead of full coverage crowns to retain a pontic (Boitel 1969). A common problem was the loss of retention of a retainer, with subsequent secondary caries development (Roberts 1970). As a result, more effective intracoronal retention with the help of boxes, grooves, and pins was demanded (Weinberg 1970). These solutions, however, mitigated the advantage of minimal invasiveness compared with complete-crown retainers. In the 1980s, adhesive techniques allowed the luting of metallic frameworks to dental enamel by using metal retainer wings made of cast gold or non-precious metal (Rochette 1973, Livaditis 1983). Inadequately retentive preparation shapes and insufficient stability of the metal framework were perceived to have been contributing factors. After initially frequent losses of retention, more defined and retentive preparations, along with improved adhesives, led to acceptable retention rates, especially in anterior teeth (Rammelsberg et al 1993). The aesthetic limitations caused by the metallic framework remained a problematic issue. The dark framework on the oral surfaces of abutment teeth eliminated translucency and gave the teeth a greyish appearance (Livaditis 1983) Restorations made of metal alloys are characterized by certain basic disadvantages. These base metal components that form on the surface of the alloy during the metal-ceramic fusing process may have a negative effect on the adjacent soft tissue. In addition, the opaque, darkish appearance created by certain metal denture retainers in the abutment teeth is considered to be unattractive. Partial preparations like inlays, onlays or partial crowns are recommended as retainers for short-span FPDs in caries-resistant dentitions. In addition to facilitating superior periodontal health, partial retainers enable preservation of healthy tooth structure. The combination of highly translucent prosthodontic materials and resin composite cements has enhanced the use of the adhesive technique and launched a new era of restorative treatment options with promising initial clinical results (Sorensen et al 1999). New in vitro findings and a better understanding of stress formation in fiber-reinforced composite (FRC) (Vallittu 1996, Freilich et al 2004) and in all-ceramic restorations led to less invasive preparations extended to existing systems. There has been limited use and no published clinical data of all-ceramic posterior FPDs retained either by wings or

8 inlays, mostly because of the low strength, the strength scatter, and the time- dependent strength decrease of ceramics owing to slow crack growth (Fischer et al 2003). The reduced invasiveness of these resin-bonded inlay-retained FPDs makes them an appealing alternative to conventional preparations in cases where the residual dentition exhibits low caries activity. Metal-free materials such as fiber- reinforced composites or high strength pressed ceramics exhibit outstanding corrosion resistance. The esthetics properties of these systems must be attributed to the high translucency of the materials and the fact than the restorations are entirely fabricated of tooth-coloured materials thereby achieving a high degree of light transmission. However, restorations made of these materials are not as strong as those that are metal-supported because of their particular mechanical properties. To achieve adequately strong dental restorations, therefore, certain modifications are necessary in the preparations fabrications, and cementation methods. The preparation geometry on an inlay retainer offers favourable prerequisites for the adhesive cementations technique. The preparation is usually surrounded by dental enamel, and the location of the preparation margin allows a rubber dam to be placed to ensure complete isolation. Adhesive cementation could offer one of the most effective ways of countering the loss of retention, which is one of the most frequent causes of failure of conventional inlay-retained fixed partial dentures.

1.3 Indication and contraindications of inlay-fixed partial denture

The indications have to be strictly observed because of the special properties of the metal-free materials. As a result, careful assessment and planning prior to beginning the prosthodontic treatment measures are requisite. Furthermore, the following prerequisites must be met if the successful results are to be achieved with metal free- inlay-retained FPDs. 1. Good oral hygiene 2. Low susceptibility to caries 3. Parallel alignment of abutment teeth 4. Immobility of the abutment teeth 5. Minimum height of abutment teeth ≥ 5mm (connector thickness)

9 6. Maximum mesiodistal extension of the interdental gap of 9 mm (width of premolar) if pressed ceramic is used and 12 mm (width of molar) if fiber- reinforced composite materials are used. Severe parafunctions, short clinical crowns (<5mm) and extensive defects of the clinical crown, as well as the loosening of teeth because of factors related to the periodontium, have been established as contraindications. The cusps of endodontically pre-treated teeth are included in the preparation to protect them. Metal-free inlay-retained fixed partial dentures must be adhesively cemented because of the primary friction compared with metal-supported systems (Edelhoff et al 2001). Existing therapy-resistant periodontopathologic complains as well as allergies to the components of dentin adhesives or luting composites, therefore, must be classified as absolute contraindications. Gingival bleeding could compromise the adhesive bond between the resin and the prepared tooth. In preparation for adhesive cementation, therefore, all signs of periodontal inflammation should be eliminated. In addition to a thorough intraoral examination, radiographs (proximal caries, periodontum) of the designed abutment teeth and irreversible hydrocolloid impressions recommended for evaluating these factors. Special attention must be paid to generalized wear facets, the position of the antagonist contacts, existing hyperbalances, the length of the clinical crown, the pontic span, and the alignment of the abutment teeth. In addition, canine guidance must be ensured to protect the inlay- retained fixed partial denture from torsional stress. If it is not established, its reconstruction during the restorative procedures should be considered.

10 References

Boitel RH. Pin abutment for crown and bridge work. Dtsch Zahnarztl Z 1969; 24:705–707. Creugers NH, Kayser AF, van 't Hof MA. A meta-analysis of durability data on conventional fixed bridges. Community Dent Oral Epidemiol. 1994 Dec;22:448- 52. Creugers NH, Kayser AF, Van't Hof MA. A seven-and-a-half-year survival study of resin-bonded bridges. J Dent Res. 1992 Nov;71:1822-5. Edelhoff D, Sorensen JA. Tooth structure removal associated with various preparation designs for posterior teeth Int J Periodontics Restorative Dent. 2002;22:241-9. Edelhoff D, Spiekermann H, Yildirim M. Metal-free inlay-retained fixed partial dentures. Quintessence Int. 2001 Apr;32(4):269-81. Ericsson S, Hedegard B, Wennstrom A. Roentgenographic study of vital abutment teeth. J Prosthet Dent 1966;16:981-987. Fischer H, Weber M, Marx R. Lifetime prediction of allceramic bridges by computational methods. J Dent Res 2003;82: 238–242. Freilich MA, Meiers JC. Fiber-reinforced composite prostheses. Dent Clin North Am. 2004, 448:545-62. Kerschbaum T, Voss R. Practical efficacy of crowns and inlays Dtsch Zahnarztl Z. 1981 Apr;36:243-9. Klötzer WT. Die traumatische Schadigung der pulpa bei der Uberkronung. Dtsch Zahnarztl 1984;39:791-794 Kopp EN. Partial veneer retainers. J Prosthet Dent. 1970;23:412-9. Livaditis GJ. Etched metal resin-bonded restorations: principles in retainer design. Int J Periodontics Restorative Dent 1983; 3: 34–47. McLean JW. The cast metal-ceramic crown. In: The science and art of dental ceramics. Chicago: Quintessence, 1980:202. Paszyna C, Kerschbaum T, Marinello CP, Pfeiffer P. Clinical long-term results with bonded bridges Dtsch Zahnarztl Z. 1990 Jul;45:406-9. Rammelsberg P, Pospiech P, Gernet W. Clinical factors affecting adhesive

11 fixed partial dentures: a 6-year study. J Prosthet Dent 1993; 70: 300–307. Roberts DH. The failure of retainers in bridge prostheses. An analysis of 2,000 retainers. Br Dent J 1970; 128: 117–124 Rochette AL. Attachment of a splint to enamel of lower anterior teeth. J Prosthet Dent 1973; 30: 418–423. Rosenstiel SF, Land MF, Fujimoto J. The contemporary Fixed Prosthodontics. The metal-ceramic crown preparation, ed 2. St.Louis :Mosby Year Book, 1995:180-193. Schwartz NL, Whitsett LD, Berry TG, Stewart JL. Unserviceable crowns and fixed partial dentures: lifespan and causes for loss of serviceability. Am J Dent 1970;81:1395-1401. Sorensen JA, Cruz M, Mito WT, Raffeiner O, Meredith HR, Foser HP. A clinical investigation on three-unit fixed partial dentures fabricated with a lithium disilicate glass-ceramic. Pract Periodontics Aesthet Dent. 1999 Jan-Feb;11:95-106. Vallittu PK. A review of fiber-reinforced denture base resins. J Prosthodont 1996;5(4):270—6. Weinberg LA. Vertical nonparallel pin-inlay fixed partial prosthesis.J Prosthet Dent. 1970;23:420-33.

12 Chapter 2: The use of fiber reinforced composites in dentistry

Fibre-reinforced materials combine the basically different mechanical properties of fibres and a matrix, in which the fibres are embedded. The fibres demonstrate high tensile strength, a high tensile modulus, and low shear strength, while the matrix is characterized by high toughness. In an optimum fibre-reinforced material, the tensile strength of the fibre is combined with the high toughness of the matrix. Fibre- reinforced technology is used wherever high stress occurs and low weight is required, such as in the aeronautical and shipbuilding industries. Low weight combined with high strength is also required in removable denture prosthetics, for which PMMA resins have proved to be particularly suitable due to their resistance to the oral environment. Since complete dentures may fracture, glass- fibre reinforcements had been discussed by dental interest groups for decades. (Grotsch, 1965a; Grotsch, 1965b; Mc Creight, 1967). Research mainly focused on the reinforcement of PMMA denture base materials by means of fibres (Vallittu, 1996). Most scientists found that increased mechanical strength values can be achieved by means of fibre reinforcement (Vallittu, 1996), with the fracture resistance enhancing with an increasing fibre content (Vallittu et al. 1994).

2.1 Fiber-reinforced composite systems Glass fibre-reinforced composites (FRC) were introduced to dentistry in the late 1990s and were advertised as a universal aesthetic material for nearly every dental indication. Several in vitro studies confirmed good material properties and good marginal adaptation (Behret et al., 1999; Körber et al., 1996; Göhring et al., 2001, Goldberg et al., 1992; Behr et al., 1999; Karmaker et al., 1997). Composite materials are a combination of two or more distinct components forming a new material with enhanced properties. While many combinations exist, the most common composites in engineering are composed of strong fibers held by a binder or matrix. Unlike traditional materials, the properties of composites can be designed simultaneously with structural aspects. This allows composite designers to manipulate material properties by changing fiber orientation, fiber content, and geometry. Additionally, the most common types of matrix materials are polymers

13 (Barbero, 1998). Attempts have been made to reinforce dental polymers with several types of fibers for various treatment modalities during the past 30 years. Studies have tested polyethylene fibers (Ladizesky et al., 1992), carbon/ graphite fibers (Kilfoil et al., 1983; Malquarti et al., 1990; Ruyter et al., 1986), or glass fibers (Goldberg et al., 1992, Imai et al., 1999; Meiers et al., 2000; Vallittu et al., 1996). There exist potential applications for fiber-reinforced composites (FRC) in prosthodontics, periodontics, and orthodontics. Several in vitro studies have been conducted to find out and understand the factors influencing dental FRC properties (Vallittu et al., 1994; Viguie et al., 1994; Behr et al., 2000; Vallittu et al., 1998; Vallittu et al., 2000; Nohrstrom et al., 2000). Important factors influencing the mechanical properties of FRCs include:

(1) inherent material properties of fibers and polymer matrices, (2) fiber surface treatment (sizing) and impregnation of fibers with resin, (3) quantity of fibers (Lassila et al., 2002), (4) direction of fibers (5) position of fibers (Vallittu, 2002; Chung et al 1998; Ellakwa et al., 2001) (6) water sorption of FRC matrix (Lassila et al., 2002).

The main FRCs are represented by systems with different characteristics. Glass fiber–reinforced systems (Vectris; Ivoclar-Vivadent, Schaan, FL and FibreKor; Jeneric/Pentron, Wallingford, CT) use continuously oriented fibers preimpregnated with monomers ready for heat or light curing (“prepregs”). FibreKor prepregs are unidirectional and adapted manually. Vectris uses a vacuum/pressure device to shape the framework. The Vectris framework consists of 3 different prepregs that can be distinguished by the fiber orientation; prepregs with parallel fibers are called “pontic,” those with a 45-degree alignment are called “single,” and those with a 90- degree alignment are the “frame” prepregs. A third prepreg system (EverStick, Turku, Finland) comprises glass fibers preimpregnated with thermoplastic polymers. Another system (Connect-Band; SDS Belle, Orange, CA) consists of woven “plasma-etched” polyethylene fibers that must be impregnated by the user before manual adaptation. Fixation of the fibers in the matrix occurs only by mechanical means, and perfect impregnation depends on the skill of the user.

2.2 Properties of the fibers and polymer matrices

The composition of glass fibers used for dental applications varies. Continuous fibers for polymer-glass fiber composite are usually made of alkali-free glass (up to 1%

Na2O + K2O) know as E-glass (electrical glass). E-glass is based on the SiO2-Al2-O3- CaO-MgO system, which has good glass-forming ability. Because of the high calcium oxide (CaO) content, glass similar to this composition shows poor resistance to acidic solutions. For this reason, the composition of E-glass is modified by introducing boron oxide (B2O3) and by decreasing the CaO content (Hlavác, 1983). The composition for E-glass is presented in table 1. Four other types of glass used in polymer-fiber composites, S-glass and R-glass (both high-tensile-strength glass), acid-resistant, and alkaline-resistant glass, are also included. Glass composition influences the hydrolytic stability or corrosion resistance of the fibers (Ehrenstein et al., 1990). The amount of B2O3 in glass fibers influences the hydrolytic stability of the glass fiber surface. B2O3, which lowers surface energy of the molten glass, may concentrate in the surface layers of the glass fiber during the production process

(Loewenstein, 1966). Because B2O3 is exceedingly reactive with water (Loewenstein, 1966), susceptibility of the glass fiber-polymer interface to hydrolytic degradation in the presence of B2O3 may be increased if the composites are used in an aqueous environment. Unidirectional glass fibers are fiber rovings or yarns consisting of 1.000 to 200.000 single glass fibers. Unidirectional fibers give anisotropic mechanical properties to the composite, and are suitable for applications in which the direction of highest stress is known. For example, the fibers can be used to efficiently reinforce polymers in one direction if there is adequate adhesion between the polymer and the fibers. Possible uses of this type of material in prostheses would include the pontics of the fixed partial denture and some removable partial denture designs (Vallittu, 1997). Bidirectional weaves reinforce structures in two directions and are therefore useful when the direction of highest stress in the prosthesis is difficult to predict. The rovings or yarns can be woven in different weaves in which the fibers are oriented in two directions. The weaves may have various textile structures, such as linen, twill, or satin weave (Airasmaa et al., 1994). The efficiency of bidirectional fiber

15 reinforcement (fibers at a 45° angle to the force) is ½, in the contrast to unidirectional fiber reinforcement, which has a reinforcing efficiency of 1. Examples of indications for bidirectional weaves may be resin crowns and some types of removable partial dentures, such as overdentures.

Table 1. Composition of different glass fibers (wt%) Components E-glass Acid- Alkaline- R-glass S-glass resistant resistant glass glass

SiO2 53-55 56-58 62 60 62-65

Al2O3 14-16 12 0.8 25 20-25 CaO 20-24 17-22 5.6 6-9 - MgO * 2-5 - 6-9 -

B2O3 6-9 - - - 0-1

K2O ≤1 0.4 - 0.1 -

Na2O § 0.1-2 14.8 0.4 0-1

Fe2O3 § 0.2-2 - 0.3 0.2

ZrO2 - 2 - - - ZnO 0-0.7 2 0 - - * Total amount of CaO and MgO is 20-24wt%-

§ Total amount of K2O, Na2O, and Fe2O3 < 1wt%.

2.3 Impregnation of the fibers Many authors have investigated the impregnation of the fibers with the matrix because poor impregnation creates problems using FRC in dentistry. (Miettinen et al., 1999; Vallittu et al 1998). Fiber reinforcement is only successful if the loading force can be transferred from the matrix to the fiber. In the case of voids between the matrix and the fiber, the load-bearing capacity of the FRC decreases. Poorly impregnated fibers cause another problem: the increase in water absorption in FRC Issac, 1999; Miettinen et al., 1999; Jancar et al., 1993) which reduces the mechanical properties (Söderholm et al., 1990; Söderholm et al., 1984). Voids and cracks in the laminate allows water to enter. A reliable adhesion between the fibers and the matrix reduces voids and cracks, which can limit the water absorption. In the case of glass fiber-reinforced reconstructions, the fibers are covered with a silane-

16 coupling agent. Plueddemann postulates a condensation reaction between the silanol groups and the glass surface (Plueddemann, 1982). The more siloxane bridges that exist, the less water will be absorbed resulting in more adhesion between matrix and fibers. Furthermore, the composition of the glass fibers is particularly important. The content of alkali and earth-alkali ions and boron oxide has to be considered due to the increased reactivity of these ions and oxides to water. The mechanism of hydrolytic degradation is based on the leaching effect of boron oxide from the glass surface (Vallittu, 1999). It should be noted that by correct treatment of the glass fibers in the sizing procedure, the corrosion of the glass fiber surface could be diminished. Thus, glass fibers from different manufactures and with different surface chemistry might behave differently in this respect. Furthermore, voids of poorly impregnated fibers are oxygen reserves (Vallittu, 1999). The oxygen inhibits radical polymerization of the polymer matrix. This decreases the strength of the FRC and increases the residual monomer content, which can lead to irritant reactions in the oral mucosa (Hensten-Pettersen, 1998) To solve all these problems, pre-impregnated (pre-pregs) FRC are used. Pre- impregnated means that the glass fibers are covered with a silane coupling agent and then pulled through convoluted paths around supports with a bath of light- and/or heat-curable monomer systems of polymers (Goldberg, 1999). Pre-pregs of various sizes can be produced to facilitate clinical application. In dentistry, generally three systems are used to form fiber-reinforced frameworks for fixed partial dentures with pre-impregnated glass fibers. One system, like Vectris (Ivoclar, Schaan, FL) is based on a vacuum/pressure adaptation of the fibers in a mold (Unterbrink, 1999). The purpose of this procedure is to maximize the fiber content, decrease the number of voids in the framework, and reduce the technique sensitivity in order to improve the mechanical properties. Other systems, like FibreKor (Jeneric/Pentron, Wallingford,CT), prefer a manual adaptation of the pre- impregnated fibers. (Freilich et al., 1998). The advantage of this procedure is said to reduce the equipment needed in its manufacturing. The third system (Stick, Stick Tech Ltd, Turku, Finland) is based on pre-impregnated glass fibers with thermoplastic polymers, which form a multiphase polymer matrix for FRC with light-curing monomers.

2.4 Quantity of fibers The strength of a fibre-reinforced material depends on the volume content of the fibres. The better the densification of the glass-fibre, the higher the mechanical strength will be (Agarwal et al.,1990; Zanghellini, 1997). Highly densified fibre elements, however, are too rigid to be formed at will. Therefore, Vectris is pressed into the desired form and simultaneously densified during the forming procedure in the VS 1. Subsequently, the matrix is polymerized with light, which secures the shape of the framework (Fig. 1).

Fig.1. Scanning electron microscopic image of the cross-section of Vectris Pontic fibres before (left) and after (right) densification in the Vectris VS1 device. (Courtesy of Dr. Urs Lendenmann)

2.5 Direction of the fibers In dental reconstructions, unidirectional and bi- or multidirectional fiber orientation is used. Unidirectional fibers produce anisotropic mechanical properties in the composite (Goldberg et al., 1994; Issac, 1998; Jauss, 1997; Vallittu, 1998) and are preferred when the direction of the highest stress is known. In other cases the rovings can be woven in such a way that the fibers are oriented in two or three directions, giving the FRC so-called orthotropic mechanical properties (Vallittu, 1998). However, the efficiency of woven multidirectional fiber reinforcement is reduced as described in the Krenchel-formula (Elias, 1992). Numerous articles demonstrate the relationship between the quantity of fibers in the polymer matrix and the enhancement of the flexural, transverse and impact strength of fiber-reinforced reconstructions (Zanghellini, 1992) has been described that with increasing fiber content, the flexural strength increases linearly. The fiber quantity in the polymer matrix should be defined in volume not weight percentage. In the case of carbon-, aramid- or ultra-high-modulus polyethylene fibers (UHMPE), which have a lower density than glass fibers, the fiber content can lead to misleading results with regard to the strength of FRC (Vallittu, 1998). Vallittu describes a formula to transform fiber weight percentage into volume percentage (Vallittu, 1997).

2.6 Position of fibers Previous dental FRC research on position and orientation has focused upon the effects of the question of fiber reinforcement directionality (i.e. random or longitudinal orientations) (De Boer, 1984; Galan et al., 1989). It is widely accepted that directional orientation of the fiber long axis perpendicular to an applied force will result in strength reinforcement. Forces that are parallel to the long axis of the fibers, however, produce matrix-dominated failures and consequently yield little actual reinforcement. Design strategies are on occasion employed to provide multidirectional reinforcement, to minimize the highly anisotropic behavior of unidirectional fiber reinforcement. Multidirectional reinforcement, however, is accompanied by a decrease in strength in any one direction when compared with unidirectional fiber, as described by Krenchel (Vishu, 1998). In most instances in the dental literature, fiber reinforcement has been positioned in the center of a composite specimen (De Boer, 1984). Yet from engineering applications, it is known that the position and orientation of the reinforcement within a construction influences mechanical properties (Hull, 1990). For a small sized construction, such as a dental prosthesis, the quality and characteristics of the FRC are important and demand careful attention. Fiber reinforcement should be optimal when designing prostheses and their components. As an example, the components (e.g. connector, pontic, retainer) of a FRC fixed partial denture (FPD) need to be designed to withstand masticatory loading (Dyer, 2002). While it is known that tension side fiber reinforcement strengthens a loaded construction, the effect of varying the cross- sectional design in a FRC structure is not fully known. Respectively, all factors relating to design and failure of FRC structures should be investigated and better understood. In conclusion, position and fiber orientation influenced the load to initial and final failure, and specimen deflection. Tension side reinforcement was most effective in increasing the load to initial and final fracture (Dyer et al., 2004).

2.7 Water sorption of FRC matrix Glass fibers are those most often used for reinforcing polymers in prosthetic dentistry because of the good aesthetic qualities of glass fiber (Vallittu, 1997) and goog bonding of glass fibers to polymers via silane coupling agents (Rosen, 1978; Mittal,

19 1992; Vallittu, 1997). The most common type of glass used in fiber production is the so-called E-glass (electrical glass), and this type of glass is also most often used in dental fiber composites (Vallittu, 1998). An aqueous environment, such as in the oral cavity, can induce “corrosion” effects in the surface of glass fibers resulting from water that diffuses through the polymer matrix (Ehrenstein GW, 1990). This can lead to a reduction of the mechanical properties and changes in the composite structure, because the surface of the glass fibers is affected by the hydrolysis of alkali and earth alkali oxides in the glass and leaching of ions. The composition of the glass is therefore decisive for the hydrolytic stability of the glass fibers. The silanization used to bond the fibers to the polymer matrix also influences the hydrolytic stability of the composite (Pantano et al., 1992). The polymers used in prosthetic dentistry are often multiphase acrylic resin systems made from prepolymerized powder beads (predominantly poly[methyl methacrylate] or PMMA) and a liquid of monomers such as methyl methacrylate (MMA) with ethyleneglycol dimethacrylate (EGDMA) or 1,4-butanediol dimethacrylate (1,4- BDMA) as cross-linking agents. (Ruyter et al., 1982 ; Öysaed et al., 1982; Öysaed et al., 1989; Hill, 1981). Water sorption of such multiphase acrylic resins is approximatively 2wt% (Al-Mulla et al., 1989; Kalanchandra et al., 1987a; Kalanchandra et al., 1987b; Miettinen et al., 1997). The cross-linking agent EGDMA has little effect on the water sorption of denture base polymers (Jagger et al., 1990; Arima et al., 1996). In a fiber-polymer composite, the water sorption is also affected by the impregnation of fibers with a resin. If there are regions in which the fibers are not completely embedded with resin, there will be voids in the structure of cured composite that increase water sorption (Peltonen, 1992; Vallittu, 1995a; Vallittu, 1995b). In conclusion, water has a plasticizing effect resulting from interaction with the polymer structure (Ruyter et al., 1986). Many studies on the water sorption of denture base polymers have been carried out, and it has been concluded that water sorption decreases the mechanical properties of denture base polymers (Hargreaves, 1979).

20 Fig.1 The picture shows the structure of the fiber- reinforced composite. On the left side there is the veneering composite (Targis; Ivoclar- Vivadent) and on the right side the fiber of pontic (Vectris; Ivoclar-Vivadent) embedded of Bis-GMA 24.5% and triethylene glycol dimethacrylates 6.2% with 65% of glass fibers.

Fig.2 The weave glass fibers of frame (Vectris; Ivoclar-Vivadent) are moistly constituted of Bis-GMA 35.2% and triethylene glycol dimethacrylates 8.8% with 50% of glass fibers.

Fig.3 The glass fiber is 10 mm of diameter.

References

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22 Grotsch G. Glasfaserverstärkte Kunststoffe (GFK). Quintessenz 1965a;16:109- 10. Hargreaves AS. Equilibrium water uptake and denture base resin behaviour. J Dent 1979; 6:342-349). Hlavác J. Glass technology, Hlavác J (ed): The technology of glass and ceramic. An Introduction (ed 1). Amsterdam, Elsevier, 1983 pp 55-220. Hull D. An introduction to composite materials. Cambridge: University Press; 1990. pp. VII, 24—5, 36—7. Imai T, Yamagata S, Watari, F, Kobayashi, M, Nagayama K, Toyoizumi H, Uga M, Nakamura S. Temperature-dependence of the mechanical properties of FRP orthodontic wire. Dent Mater J 1999;18(2):167—75. Kilfoil BM, Hesby RA, Pelleu Jr GB. The tensile strength of a composite resin reinforced with carbon fibers. J Prosthet Dent 1983;50(1):40—3. Körber KH, Körber S. Mechanische Festigkeit von Faserverbundbrücken Targis/Vectris. ZWR 1996; 105: 693–702. Ladizesky NH, Ho CF, Chow TW. Reinforcement of complete denture bases with continuous high performance polyethylene fibers. J Prosthet Dent 1992;68(6):934—9. Lassila LV, Nohrstrom T, Vallittu PK. The influence of short-term water storage on the flexural properties of unidirectional glass fiber-reinforced composites. Biomaterials 2002;23(10):2221—9. Loewenstein KL. Glass systems in Holliday L (ed). Composite materials (ed 1). Amsterdam, Elsevier, 1966 pp 129-287. Malquarti G, Berruet RG, Bois D. Prosthetic use of carbon fiber-reinforced epoxy resin for esthetic crowns and fixed partial dentures. J Prosthet Dent 1990;63(3):251—7. Mc Creight LR. Overview of fiber composites. J Dent Res 1967;46:1192. Meiers JC, Freilich MA. Conservative anterior tooth replacement using fiber- reinforced composite. Oper Dent 2000; 25(3):239—43. Mittal KL. Reminiscing of silane coupling agents. In: Mittal (ed). Silanes and other coupling agents. Utrecht VSP, 1992:3-12. Nohrstrom TJ, Vallittu PK, Yli-Urpo A. The effect of placement and quantity

23 of glass fibers on the fracture resistance of interim fixed partial dentures. Int J Prosthodont 2000;13(1):72—8. Oysaed H, Ruyter IE.Water sorption and filler characteristics of composites for use in posterior teeth. J Dent Res. 1986;65:1315-8. Pantano CG, Carman LA, Warner S. Glass fiber surface effects in silane coupling. In: Mittal KL (Ed). Silanes and Other Coupling Agents. Utrecht VSP, 1992:229-240. Peltonen P Järvelä P. Methodology for determining the degree of impregnation from continuous glass fibre prepreg. Polymer Testing 1992;11:215-244). PK, Lassila VP, Lappalainen R. Transverse strength and fatigue of denture acrylic—glass fiber composite. Dent Mater 1994;10(2):116—21. Rosen MR. From treating solution to filler surface and beyond. The life history of a silane-coupling agent. J Coat Tech 1978;50:70-82. Ruyter IE, Ekstrand K, Bjork N. Development of carbon/graphite fiber reinforced poly (methyl methacrylate) suitable for implant-fixed dental bridges. Dent Mater 1986;2(1):6—9. Ruyter IE, Oysaed H. Conversion in different depths of ultraviolet and visible light activated composite materials. Acta Odontol Scand. 1982;40:179-92. Vallittu PK, Lassila VP, Lappalainen R. Acrylic resin-fiber composite--Part I: The effect of fiber concentration on fracture resistance. J Prosthet Dent 1994;71:607-612. Vallittu PK. A review of fiber-reinforced denture base resins. J Prosthodontics 1996;5:270-276. Vallittu PK. Compositional and weave pattern analyses of glass fibers in dental polymer fiber composites. J Prosthodont 1998;7(3):170—6. Vallittu PK. Curing of a silane coupling agent and its effect on the transverse strength of autopolymerizing polymethylmethacrylate-glass fibre composite. J Oral Rehabil. 1997 Feb;24(2):124-30. Vallittu PK. Effect of 180-week water storage on the flexural properties of E- glass and silica fiber acrylic resin composite. Int J Prosthodont 2000;13(4):334—9. Vallittu PK. Glass fiber reinforcement in repaired acrylic resin removable dentures: preliminary results of a clinical study. Quintessence Int. 1997 Jan;28(1):39-44.

24 Vallittu PK. Some aspects of the tensile strength of undirectional glass fibre- polymethyl methacrylate composite used in dentures. J Oral Rehabil. 1998 Feb;25(2):100-5. Vallittu PK. Strength and interfacial adhesion of FRC-tooth system. In: Vallittu PK, editor. The Second International Symposium on Fibre-Reinforced Plastics in Dentistry. Symposium Book on the Scientific Workshop on Dental Fibre- Reinforced Composite on 13 October 2001 in Nijmegen, The Netherlands; 2002. Viguie G, Malquarti G, Vincent B, Bourgeois D. Epoxy/carbon composite resins in dentistry: mechanical properties related to fiber reinforcements. J Prosthet Dent 1994; 72(3):245—9. Vishu S. Handbook of plastic testing technology, 2nd ed. New York: John Wiley; 1998. pp. 546. Zanghellini G (1997). Faserverstärkung – die Festigkeit ist eine Funktion des Volumenanteils der Fasern im FRCWerkstoff. Phillip J 14:390-393.

25 Chapter 3: Marginal adaptation of inlay-fixed partial dentures

Missing single-tooth situations offer several reconstructive treatments modalities. The traditional way is the reconstruction with a conventional metal-ceramic fixed partial denture (FPD) (Valderhaug 1991). This technique requires a full-coverage preparation of the abutment teeth. Consequently, a large quantity of sound tooth structure is destroyed during the preparation (Edelhoff et al 2002). This is particularly problematic in healthy and young teeth with large pulpal chambers. In order to limit this destruction and thanks to the evolution of adhesive dentistry, (Perdigão et al 1999) and implantology, adhesive fixed partial dentures (AFPD) (Freilich et al 1998) and dental implants ( Leal et al 2001) represent the current alternatives. These treatments have several advantages over conventional bridges, especially in relation to conservation of tooth structure and their reversibility (Lutz et al 2000). Nevertheless when an implant is contraindicated or refused by the patient, metal-free restorative options may become attractive. Better bonding properties to composite cements, more appropriate biomechanical behaviour, and enhanced aesthetics are expected with the use of composite or ceramic compared to metal alloys. Inlay-, onlay- and partial crown-anchored FPDs can be bonded to the adjacent teeth and show acceptable short-term results (Göhring et al 2002, Monaco et al 2003). Fiber reinforced composites (FRC) (Krejci et al 1998), high-strength reinforced ceramics (Edelhoff et al 2001) and a combination of these two materials (Rosentritt et al 2003) have been proposed for the fabrication of metal-free inlay fixed partial dentures (IFPDs). Physical data on reinforced composites suggest that these materials are best suited for conservative inlay FPDs (Göhring et al 1999). With a carefully executed bonding technique, good results in marginal adaptation have been achieved with composite inlays (Lutz et al 1991). The stress-resistant marginal integrity of composite inlays has been attributed to their dentin-like elasticity modulus (Krejci et al 1994, Braem et al 1995) The following study regards the different marginal adaptation measured as continuous/noncontinuous margin of three materials with different Young modulus.

26 FRC are a new material group with a significantly shorter history of use than more traditional materials. Glass fibers have been reported to considerably improve the strength of dental polymers when the fibers were silanated and preimpregnated with the polymer (Karmaker et al 1997). The combination between resin composite and fiber seems to better comply with stress and provides a straightforward approach in the laboratory procedure because casting is not necessary (Vallittu 1999). After simulation of oral stresses, the fracture resistance and marginal adaptation of IFPDs made with FRC were better than the ones of all-ceramic restorations (Loose et at 1998). The interest of clinicians in all ceramic systems is rapidly increasing as stronger and tougher materials are developed and commercialized along with novel processing technologies. This development has recently led to the application of zirconia-based ceramics in dentistry. Moreover, the computer aided design-computer aided manufacturing (CAD-CAM) is among the most recent advances in dental technology for direct fabrication of all-ceramic restorations (Wiedhahn et al 2000). The framework must then be veneered with conventional feldspathic porcelain in order to achieve the appearance of the natural dentition. Adjustments by grinding may then be required to improve the fitting of the restoration, and sandblasting of the inner surface of the restoration is commonly used to enhance the adhesion of the luting agent to the framework (Kern et al 1998). Yttrium oxide is a stabilizing oxide added to pure zirconia (Y-TZP) to stabilize it at room temperature and to generate a multiphase material known as partially stabilized zirconia. The high initial strength and fracture toughness of Y-TZP results from the physical property of partially stabilized zirconia. The ability of Y-TZP, so-called ‘‘transformation toughening’’, to transform from tetragonal crystalline structure to a more voluminous monoclinic structure that helps to prevent crack propagation, contributes to the strength and toughness of the ceramic (Ardlin 2002, Williams 1997). In vitro studies of Y-TZP specimens demonstrated a flexural strength of 900 to 1200 MPa. Y-TZP-based materials have demonstrated a fracture toughness of 9-10 MPa/ m½, which is almost double the value demonstrated by alumina-based materials, and almost 3 times the value demonstrated by lithium disilicate–based materials (Christel et al 1989). An in vitro study evaluating Y-TZP FPDs under static load demonstrated fracture resistance of more than 2000 N (Tinschert et al 2001).

27 Points in question are the loading forces that can be withstood as well as the quality of marginal adaptation that might be reached with FRC and high strength ceramic systems when used for IFPD restorations. The most relevant mechanical properties to reduce the clinical failures during loading are flexural strength and fracture toughness but little information is available on IFPDs. Since mechanical failure is mainly caused by excessive stresses or deformation that can have a destructive effect on tooth-restoration interface, a full understanding of stress fields developed in the dental bridge becomes particularly important. On one hand, some studies with finite element analysis (Magne et al 2002, Tanimoto et al 2004) suggest that inlay FPDs made with FRC may be a viable alternative to traditional more invasive FPDs. Resiliency of the composite may prevent the development of harmful stresses at the adhesive interface, and reinforcement of the fibers may protect the pontic from excessive strains, resulting in the restoration’s ability to withstand high functional loads. On the other hand, zirconia-ceramic IFPDs exhibited the highest resistance to fracture when compared to metal-ceramic and glass-ceramic and the failures of the all-ceramic bridges were always cohesive; located at the connector area that represent the weakest parts of the bridge (Kılıçarslan et al 2004). These studies provided insight into a number of biomechanical issues, yet they did not reveal the marginal adaptation at the tooth/restoration interface during occlusion and clenching. Although there was positive mechanical behaviour of the new tested materials, further investigations should be performed on the marginal quality of these materials. The aim of this in vitro study was to evaluate the marginal adaptation using quantitative scanning electron microscope analysis of inlay FPDs made with fiber- reinforced composite and different ceramic high strength materials after simultaneous thermal cycling and mechanical loading under the simulation of dentinal fluid that simulated approximately five years of oral service. The null hypothesis was that there is no difference in marginal adaptation of the IFPDs before and after fatigue using materials with different flexural strength and Young’s modulus.

28 MATERIALS AND METHODS Thirty-six human caries-free molars and premolars of nearly identical size with completed root growth and stored in a 0.1% thymol solution were selected for this study. The teeth were randomly and equally divided into 3 groups. The apex of each root was sealed with an adhesive bonding system and resin composite (Optibond FL, Kerr; Miris, Coltene, Switzerland) without removal of pulpal tissue and fixed with the composite on aluminum bases. Afterwards, the teeth and aluminium bases were immersed in an autopolymerizing resin (Technovit 4071, Heraeus-Kulzer, Friedrichsdorf, Germany) to an apical depth of two thirds of the root length to create a strong load-resistant support. Each couple of teeth (one molar and one premolar) were blocked together with the same autopolymerizing resin at a distance of 10 mm to each other to prevent movement during the preparation, impression and luting procedures. In this way, the device simulated an edentulous space resulting from the loss of one molar. A plastic holding device with 2 holes was used as a support for the inlay bridges. Two rubber dampers that were slightly taller than the holes were inserted in the holding device. Eccentric holes were drilled into the rubber dampers to create a larger distance between the abutments and to increase the tilting of the abutments toward the space when placed under load. One holding device with the same distance between the rubber dumpers was created (Fig.1). To simulate the intrapulpal pressure during the cavity preparations and the luting procedures, a cylindrical cavity was prepared in each pulpal chamber 1,5 mm below the amelo-cementum junction. A metal tube with a diameter of 1.4mm was luted into the cavity with the same adhesive and composite used to fix them on the bases. Through a connecting silicone tube, the pulpar chamber was evacuated with a vacuum pump (Vacubrand GmbH, & Co, Wertheim, Germany), filled with a bubble-free mixture of horse serum (PAA Laboratories GmbH, Linz, Austria) and phosphate-buffered saline solution (PBS;Oxoid Ltd, Basingstoke, Hampshire, England) with the aid of a 3-way valve, and finally connected to a serum infusion bottle. This bottle was placed vertically 34cm above the specimen to simulate the normal hydrostatic pressure of 25mm Hg within the tooth until the test was terminated.

Tooth preparation

Different cavity preparations were made on the teeth to simulate a frequent clinical situation and to create the space accommodation for the different structure frameworks. The cavities were prepared with the use of rotating diamond bur (80- 25 m grain size, FG 8113NR, 3113NR; Intensiv SA, Viganello Switzerland; Sirius 180 XL red contra-angle handpiece, Micro-Mega, Bresançon, France) with water- cooling. Fig.1. The teeth were blocked together at a distance of 10 mm to prevent any movement. The device simulated an edentulous space resulting from the loss of one molar. The metal tube luted into the cavity was filled with a bubble- free mixture of horse serum and phosphate-buffered saline solution to simulate the intra pulpal pressure.

Fig.2-a. Fig.2-b. Fig.2. The onlay preparation in the molar (a) and inlay cavity in the premolar (b) had mesial margin in enamel (left) and distal margin in dentin (right). The margins were divided in different portions to analyze the marginal adaptation in a selective way. A-B: occlusal enamel, B-C, D-E: approximal enamel, C-D: cervical enamel, F-G, H-I: approximal dentin, G-H: cervical dentin.

The inlay preparation made in the premolar was a MOD cavity with mesial margin in dentin, 1 mm below the cementum-enamel junction (CEJ), and distal margin in enamel, 1 mm above the CEJ. The vestibular-palatal width was 3 mm at the cervical margin that increased to 4 mm at the upper part of the cavity; the cervical preparation breadth was 2 mm, similar to the occlusal depth. The onlay preparation made in the molar was a two cusps partial covering with mesial margin in dentin, 1 mm below the CEJ and distal margin in enamel, 1 mm above the CEJ. The vestibulo-palatal

30 width was like the premolar preparation and the reduction of the cusps was 2.5 mm, with 2 mm of occlusal depth in the central fossa (Fig.2a-b). All dentin surfaces were sealed immediately after the tooth preparation with a 3-step adhesive system (Optibond FL, Kerr; batch n°25881). Phosphoric acid (Ultraetch, Ultradent) was applied on dentin for 15 seconds and then rinsed for 30”. The primer was spread on the dentin for 30” with a microbrush without scrubbing and after, the bonding was applied to the dentin. After a minimal penetration time of 20 seconds, the resin was air-thinned and polymerized (Optilux 500, Demetron Inc, Danbury, Conn.) for 60 seconds. Butt joint cavity finishing lines were finished with a diamond bur (25mm grain size, N° 3113 NR Intensiv SA) by the use of water-cooling under a stereomicroscope (Leica MZ6). The polymerised bonding was removed with the same diamond bur only from the cavity enamel finish lines without touching the sealed dentin. Impressions were made with Imprint II polyvinyl siloxane (3M ESPE) with a simultaneous mixing technique according the manufacturer’s instructions. Provisional restorations were made with Fermit N (Ivoclar-Vivadent) and inserted without interim cement in analogy to the clinical procedure. Laboratory manufacturing process. Eighteen inlay bridges were made using three different materials with unlike flexural strengths and Young’s moduli (Tab.1). Fiber reinforced composite (SR Adoro/Vectris; Ivoclar/Vivadent) (Fig.3a-b), zirconium oxide-TZP “tetragonal zirconia polycrystals” (Cercon, DeguDent; Dentsply) and magnesia-partially stabilized zirconia (DC-Leolux; DCS Dental, Allschwil) covered with silica-based ceramics were tested in this study (Fig.3a-b).

Fig.3a Fig.3b Fig.3a-b Lateral view of the IFPD made with (a) fiber reinforced composite (Adoro/Vectris) and (b) zirconium oxide-TZP tetragonal zirconia (Cercon).

The FRC system (Group 1) consists of two materials: glass-fibers with different orientation (Vectris) and a microfilled composite (Adoro) for the veneering of the fiber framework. The design of the fiberglass framework was first pre-modelled with a photo-curing resin (Spectra Tray, Ivoclar) to obtain the oval shape and its thickness checked on to the moulding model. This model was embedded in a transparent

31 silicone impression paste (Transil) to form a mould. Then this resin was removed and the fibers were applied into the silicone-mould. The pre-impregnated ‘pontic’ fibers were condensed in a deep-drawing, polymerization process. After a cycle of vacuum- forming process and then cured by light in VS1 unit (Ivoclar-Vivadent) for 10 min. according to the manufacturer’s recommendations, the FRC was sandblasted with Rocatec system (3M ESPE) with small grain size of 80µm at 2,5 bar of pressure for 10 seconds and treated with silane (Wetting agent, Ivoclar-Vivadent). A sheet of wave fibers ‘frame’ was placed upon the ‘pontic’ structure and the cycle in VS1 was repeated. The Adoro material was built incrementally using the Quick pre-curing light unit. The final polymerization / tempering was performed in the Lumamat 100 unit by means of light and heat. The additional tempering step at 104°C was done to maximize the strength and the surface quality of the restorations. Cercon (Group 2) is a CAM system that can produce a framework of zirconium oxide-TZP. The Cercon brain machine automatically mills the framework from an unsintered zirconium oxide blank (Cercon Base). After that the chalky-soft state is sintered in the Cercon heat furnace at 1350°C. Finally, the framework is veneered with low-fusing dental ceramic (Cercon ceram S), which is specially tailored to the coefficient of thermal expansion of zirconium oxide. The principle of the Precident system DCS (Group 3) is based on touchless contact- free measurement and milling in a CAD/CAM process. These two operations are separated for organizational reasons. The data of the abutments are taken with the help of a non-contact laser (Preciscan) that at maximum resolution can take 300.000 points/minute. The acquired data are transferred by modem to the milling machine (Precimill) that can prepare the sub-structure from a sintered magnesia-partially stabilized zirconia DC-Leolux. Finally the framework is covered with low-fusing ceramic (Cercon ceram S). The framework of the ceramic bridges (group 2 and 3) was extended until 1 mm of the margins of the cavity preparation in order to have etchable silica-based ceramic on the closing margins and optimize the adhesion with tooth tissue. All the connections of the inlay/onlay with the pontic elements were 3.5X3.5 mm. Adhesive Procedure

32 The provisional restorations were removed and the inner surfaces of the teeth previously sealed with bonding were sandblasted with CoJet system (3M ESPE) with small grain size of 30 µm at 2 bar of pressure for 2 seconds. The inner surfaces of the FRC and only the zirconium area of the ceramic bridges were treated with CoJet system (30µm at 2 bar x 10s). The closing ceramic margins were etched with 10% hydrofluoric acid for 60 seconds and 2 layers of silane-coupling agent (Monobond S, Ivoclar Vivadent) were applied and heated for 1 minute (ID 500; Coltene Switzerland) on all the inner surfaces. All enamel and dentin surfaces were luted with Optibond FL and Tetric Transparent (Ivoclar-Vivadent) by applying the ultrasonic technique according to the manufacturer’s instructions. The luting cement was light activated for 60 sec. each from cervical, buccal, lingual and occlusal surfaces. The margins of the restorations were then finished with 15µm diamond burs (Composhape, Intensiv) and polished with a composite finishing and polishing kit (Hawe Neos Dental) in a slow-speed handpiece (Fig.4).

Fig.4 Adhesive inlay bridge made in fiber reinforced composite after the luting procedures.

Evaluation The samples were cleaned with rotating nylon brushes (Hawe Neos) and toothpaste (Signal Anti Caries) before making the impressions for the replicas. Seven partial impressions for each bridge before and after the thermal and mechanical test were taken to compare the quality of the marginal adaptation. Six different categories (approximal enamel, approximal dentin, cervical enamel, cervical dentin, occlusal and buccal enamel) were recorded to identify the areas with greater stress (Fig. 5). Gold sputtered (SCD 030, Provac, FL-9496 Balzers, Liechtenstein) epoxy resin replicas (Epofix, Struers, D-2610 Rodovre, Denmark) of all samples were fabricated by using polyvinylsiloxane impressions (President Plus Light-body, Colténe AG, Altstätten, Switzerland). They were subjected to a quantitative evaluation of marginal

33 adaptation at a standard 200x magnification in the SEM (XL20, Philips, NL-5600 Eindhoven, Netherlands) by using a custom made module programmed within an image processing software (Scion Image, Scion Corp, Frederik, MA 21703, USA). All specimens were subjected to the quantitative evaluation and examined for continuous margins (no gap, no interruption of continuity), non-continuous margins (gap due to adhesive or cohesive failure; fracture of restorative material or fracture of enamel related to restoration margins), overhangs and underfilled margins. The percentages of continuous/non-continuous margin were evaluated separately for tooth-luting composite and luting composite-restoration interfaces. The specimens were mechanically loaded at the vestibular cusp of the pontic element in a computer- controlled masticator with 1.200.000 cycles of 49 N each, at a frequency of 1.7 Hz. A total of 3,000 thermocycles of type 5°C to 55°C to 5°C were performed simultaneously (Fig.6). The chamber was automatically emptied after 2 minutes for 10 s with air pressure to avoid mixing the cold and warm water (Krejci et al 1990a, Krejci et al 1993). By having the specimen holders mounted on a rubber rest, a sliding movement of the bridges was produced during the loading. These conditions are believed to simulate approximately five years of clinical service (Krejci et al 1990b, Krejci et al 2003). Differences in means were compared with the use of matched pairs t tests and one-way analysis of variance (ANOVA). The level of significance was set at P=0.05.

legend Kind of replica P: premolar, M: molar

1. a

DM Distal molar d Approximal enamel: a-b; c-d

Cervical enamel: b-c b c 2. a d MP Mesial premolar Approximal dentin: a-b; c-d

bc Cervical dentin: b-c 3. a

VP Vestibolar premolar d VM Vestibolar molar c BM Buccal molar b e f P; Approximal enamel: a-b

M; Cervical dentin: c-d Approximal dentin: d-e Buccal enamel: e-f

4. a c

PP Palatal premolar d b PM Palatal molar e P; Approximal enamel: a-b

M; Approximal dentin: c-d Cervical dentin: d-e

5. a b f e

OP Occlusal premolar OM Occlusal molar c d

P; occlusal enamel: a-b; c-d

M; occlusal enamel: e-f

GP Gingival premolar

7. GM a b c d Gingival molar P; cervical enamel: a-b

M; cervical dentin: c-d

Fig. 5. Outline of the non-destructive replica technique.

Fig.6. (Left) Loading machine with six watertight cells (A) and the thermocycle device (B). (Right) The arrow down indicates the rubber dampers that increase the tilting of the abutments when placed under load. The finger point to the silicone tube filled with a mixture of horse serum and phosphate-buffered saline solution to simulate the intra pulpal pressure during all stress cycles. The dot arrow shows the level of the water during the thermocycles.

RESULTS All restorations were in place after completing the stress test, meaning that the retention amounted to 100% for all groups. Neither restoration nor abutment fractures was found after fatigue loading. Only two hairline fractures of the veneering material that spread in the buccal and vestibular area were found in the gingival part of the connection between the pontic and the abutment tooth in the FRC group (Fig. 10a-b). Marginal adaptation was analyzed at the interface of the luting composite and the abutment inlay/onlay (CI) and at the interface of the tooth and luting composite (TC). The results of the marginal adaptation expressed in percentage are represented in table 1. Significant statistical differences (P<0.05) were found for all groups before and after loading concerning the percentage of continuous margins (CM) as the total marginal length at the luting cement-restoration and luting cement-tooth interfaces. No differences were observed after the cycle test between the three groups at the luting cement-restoration interface (Fig.7). However, significant statistical differences were found after loading between the FRC and the other two ceramic systems at the luting cement-tooth interfaces (Fig.8). The prevailing marginal defect in all groups was pure marginal opening (Fig.11a-b). Some fractures pointed out after the final observation were traced back as enamel- dentinal fractures (EF) and filling fracture (FF). No significant difference was detected in the sub-fracture of the dental tissue (EF) near the margin between the three groups. However, significant changes (P<0.05) were found in hairline cracks in the restoration (FF) along the margins between DC-Leolux (4.1%), FRC (0.4) and Cercon (1.7) after loading. In some cases non continuous “pure” margin identified as only “open margin” changed in EF or FF. No more than 0.5% of the “overhangs” and

37 “underfilled margins” were found before and after loading, with no significant differences among the groups. No difference in “continuous margin” was detected between approximal enamel and approximal dentin. The inner comparison of the same groups between the onlay preparation (molar) and the inlay cavity (premolar) didn’t show significant difference (P>0.05). Severe changes in continuous margin were detected at the tooth-luting composite interface in the dentinal margin after the test. The values were 20.8% for group 1, 53.8% for group 2 and 32.2% for the last group Statistical difference was found between Cercon and the other two groups (P<0.05).

Luting composite-inlay Adoro/Vectris Cercon DC Leolux interface (CI) Before loading 94.6 ± 3.1 92.9 ± 5 96.2 ± 2.1 After loading 88 ± 6.7 85.7 ± 6.1 82.2 ± 9.8 Luting composite-tooth interface (TC) Before loading 86.7 ± 6.7 93.3 ± 3.4 96.1 ± 2.4 After loading 62.5 ± 16.4 83.2 5.9 75.3 ± 7 Table 1. Percentage of “continuous margin” for the total marginal length before and after loading (means±SD) at the luting composite-inlay and composite-tooth interfaces.

38 100

75 Marginal adaptation luting composite-restoration interface

65 Adoro/Vectris Adoro/Vectris Cercon Cercon DC-Leolux DC-Leolux before after before after before after Fig. 7. Continuous margin at luting composite-restoration interface (CI) with quantilies (red line), means/Anova (green lines), means and standard deviation (blue line).

100

Marginal adaptation40 luting composite-tooth interface

30 1 A BEFORE 1 B AFTER 2 A BEFORE 2 B AFTER 3 A BEFORE 3 B AFTER Adoro/Vectris Adoro/Vectris Cercon Cercon DC-Leolux DC-Leolux before after before after before after

39 Fig. 8. Continuous margin at tooth-luting composite (TC).

Fig. 9. Continuous margin of FRC restoration. The left area (A) represent the enamel, the middle part the luting cement and the right share shows the restoration (C). The finger points to the luting cement-tooth interface whereas the arrow indicates the luting cement- restoration interface.

Fig. 10a. Fig. 10b. Fig. 10a. Hairline fracture of the veneering material in the gingival part of the connection between the pontic and the abutment in FRC group. The finger indicates the micro crack that spread in the vestibular area. The black frame in the upper part clearly shows at 200 magnifications (fig.10b) the fissure in the resin composite.

Fig. 11a. Fig. 11b. Fig. 11. These images show the same portion before (a) and after (b) the stress cycles. The inner area (A) represent the ceramic restoration (Cercon), the luting cement constitute the middle part (B), whereas the upper portion (C) show the dental tissue. The arrows and the fingers indicate the “continuous” (10a) and “non continuous” margins (10b) as result of the 5- year simulation period.

DISCUSSION

Although this study might have some limitations in respect to its clinical relevance, the absence of detachments or fractures of the inlay bridges suggest that both ceramic and fiber reinforced composite systems could be utilized in clinical practice. Nevertheless, some remarks must be made in regard to the quality of the margins and the hairline fractures found in the FRC group. The most critical areas in dental bridges and particularly in IFPDs are represented by the connection at the gingival portion of the pontic between the abutments because this surface constitutes the tensile side of the beam (Magne et al 1999). When occlusal forces are applied directly to the long axis of the bridge at the midspan (pontic), compressive stresses will develop at the occlusal aspect of the connector at the marginal ridge, and tensile stresses will develop at the gingival surface of the connector (Kelly et al 1995). These tensile stresses could contribute to the propagation of micro cracks located at the gingival surface of the connector through the veneering material in an occlusal direction, and may eventually result in fracture of the composite. The presence of hairline fractures in the gingival area of the pontic in two bridges of FRC group could be related to the greater flexibility of the fiber framework compared to the ceramic materials supported by zirconia framework. These micro cracks can compensate the smaller stiffness of the fiber but at any rate could determine the beginning of the delamination or fracture of the layering material. The clinical fracture resistance of IFPDs is related to the size, shape, and position of the connectors and to the span of the pontic. The basis for the proper design of the connectors and the pontic is the law of beams: deflection of a beam increases as the cube of its length, it is inversely proportional to its width, and it is inversely proportional to the cube of its height (Raigrodski 2004). Moreover, the flexibility of the beam is in direct relation to the amount and the type of the fibers that go to make up the framework. The position of the FRC layer had an effect on the flexural strength of the test specimen. The highest flexural strength was achieved when the FRC layer was located at the tension side of the test specimens. The particulate filler composite is the weakest phase of the test specimen. When it is located on the tension side, the fracture can easily initiate. The FRC structure benefits most when the tensile stresses can be transferred to the reinforcing fibers. The veneering

41 particulate filler composite is strong in compression stress and, therefore, the FRC structure requires less reinforcement fibers on the compression side (Murphy 1998). Usually, it is preferable to place the FRC laminates symmetrically relating to the FRC framework, to prevent polymerization shrinkage effect, thermal stresses, and possible deformation during polymerization (Lassila et a2004). Nevertheless, it is often very difficult to design the FRC framework to form an optimal design because of the abutment location and occlusal parameters. One theoretical assertion is that lower-elastic modulus frameworks would determine a better stress transfer to the tooth and reduce tensile stresses at the adhesive interface (Vallittu et al 2000), even though no scientific evidence has shown this to be true. Vallittu (Vallittu et al 2004) supposed that a lower modulus of elasticity might allow the FPD to deflect to some extent during function without the formation of stresses that may cause debonding. Brunton (Brunton et al 1999) preferred restorative materials such as fiber-reinforced composites rather than ceramic materials because of the material’s flexibility, repairable properties, and equivalent fracture resistance. They reported that fiber-reinforced composite material showed similar fracture resistance when compared to ceramic material under compressive loads for posterior restorations. Contrary to these results, in our study the direct comparison between fiber-reinforced composite and ceramic reinforced systems suggests that different materials could have an influence on the quality of the margin primarily at the luting composite-tooth interface. In any case the null hypothesis was rejected. The statistical difference expressed in percentage between the FRC and the other all-ceramic restorations could be related to the different flexibility of the frameworks. Our results could suggest that the smaller stiffness of the fiber-composite complex can negatively influence the marginal adaptation under load. The fibre framework may absorb the stress generated during loading but the increased flexibility might have led to the opening of the margins. Any significant difference between “approximal enamel” and “approximal dentin” was found within each group for both interfaces after the fatigue test. All these margins are in enamel but deferred from the base of the cavity box. The first margin continues in the “cervical enamel”, the second keeps up in the “cervical dentin”. The opening of the margin in the cervical dentin doesn’t have an influence on the

42 overhanging enamel. The bonding between the luting composite and the enamel is so strong that the gap created at the dentin interface stopped at the cementum-enamel junction. Marginal adaptation at the dentinal margins decreased in a dramatic way after mechanical loading. The percentage of continuous margin changed from 21 to 54% after the test. A statistical difference was found between the stiffer system (Cercon) and the other two groups. In any case, the disintegration of the margins in dentin is so high in all groups that the IFPDs could be contraindicated when one or both abutments have margins in dentin until the adhesion between the luting composite and the dentin is improved. The marginal adaptation at the interface between the luting composite and restoration decreased after mechanical and thermal loading but no significant difference was found between all groups. The values ranged between 82,2 and 88%. Successful ceramic-resin bonding is achieved by the formation of chemical bonds and micromechanical interlocking at the resin-ceramic interface. With conventional silica-based ceramics, acid etching and application of a silane coupling agent create a rough surface of increased wettability for successful ceramic resin bonds. Zirconium- oxide ceramics are not silica based and the application of acidic agents, such as hydrofluoric acid, does not create a sufficiently roughened surface for enhanced micromechanical retention. Advances in adhesive dentistry have resulted in the recent introduction of modern surface conditioning methods such as silica coating that require airborne particle abrasion of the surface before bonding in order to achieve high bond strength. In this technique, the surfaces are air abraded with aluminum oxide particles modified with silica (Kern et al 1998, Özcan 2002). The blasting pressure results in the embedding of silica into the ceramic surface, rendering the silica-modified surface more chemically reactive for the resin through silane coupling agents. The tribochemical silica coating followed by silanization, which increased the silica content on the ceramic surface, evidently enhanced the bond between the ceramic surfaces and the luting cement. Since the silica layer is well attached to the ceramic surface, this provides a basis for silanes to enhance the resin bond. Airborn particle abrasion with Al2O3 abrasive particles has proven to be effective both for composite, aluminum- and zirconium-oxide ceramics (Derand et al 2000). In our study the adhesion between dental tissue and all ceramic bridges was increased leaving one millimetre or more of silica based ceramic along the margins

43 without zirconia at the interface. This treatment can explain the good results of the marginal adaptation at both adhesive interfaces of the all-ceramic systems. Within the limitations of the experimental study, several conclusions can be drawn. The flexibility of the framework may play an important role in the marginal adaptation of adhesive inlay/onlay bridges. More rigid materials may transfer the stress to the margin to smaller degree than flexible materials, which may result in a more stable bond to the dental tissues under load. When FRC are used for IFPDs high fiber volume fraction and well-designed framework shape must is mandatory to increase at maximum the stiffness of the inlay bridges. All ceramic systems reinforced with zirconia could be used for inlay FPDs in the clinical practice but simplified CAD/CAM technique is required to allow faster construction of the zirconia framework. As the marginal adaptation in dentin after load was low in all groups tested, the IFPDs might be contraindicated when abutments’ margins reach dentin independent of the bridge material used, until the adhesion between the luting cement and the dentin will be improved.

44 References

Ardlin B.I. Transformation-toughned zirconia for dental inlays, crowns and bridges: chemical stability and effect of low-temperature aging on flexural strength and surface structure. Dental Materials 2002; 18:590-95. Braem MJ, Lambrechts P, Gladys S, Vanherle G. In vitro fatigue behavior of restorative composites and glass ionomers. Dent Mater 1995;11:137- 41. Brunton PA, Cattell P, Burke FJ, Wilson NH. Fracture resistance of teeth restored with onlays of three contemporary tooth-colored resin-bonded restorative materials. The Journal of Prosthetic Dentistry 1999; 82:167-71. Christel P, Meunier A, Heller M, Torre JP, Peille CN. Mechanical properties and short-term in-vivo evaluation of yttrium-oxide-partially-stabilized zirconia. Journal of Biomedical Materials Research 1989; 23:45-61. Derand P, Derand T. Bond strength of luting cements to zirconium oxide ceramics. The International Journal of Prosthodontics 2000; 13:131-35. Edelhoff D, Sorensen JA. Tooth structure removal associated with various preparation designs for posterior teeth. The International Journal of Periodontics & Restorative Dentistry 2002; 22:241-49. Edelhoff D, Spiekermann H, Yildirim M. Metal-free inlay-retained fixed partial dentures. Quintessence International 2001; 32:269-81. Freilich MA, Duncan JP, Meiers JC. Preimpregnated, fiber-reinforced prostheses. Part I. Basic rationale and complete-coverage and intracoronal fixed partial denture designs. Quintessence International 1998; 29:689-96. Göhring TN, Mörmann WH, Lutz F. Clinical and scanning electron microscopic evaluation of fiber-reinforced inlay fixed partial dentures: preliminary results after one year. J Prosthet Dent 1999;82:662-8. Göhring TN, Schmidlin PR, Lutz F. Two-year clinical and SEM evaluation of glass-fiber-reinforced inlay fixed partial dentures. American Journal of Dentistry 2002; 15:35-40. Karmaker AC, Di Benedetto AT, Goldberg AJ. Continuous fiber reinforced composite materials as alternatives for metal alloys used for dental applicances. Journal of Biomaterials Applications 1997; 11:318-28. Kelly JR, Tesk JA, Sorensen JA. Failure of all-ceramic fixed partial dentures in

45 vitro and in vivo: analysis and modeling. Journal of Dental Research 1995; 74:1253- 8. Kern M, Wegner SM. Bonding to zirconia ceramic: adhesion methods and their durability. Dental Materials 1998; 14:64-71 Kern M, Wegner SM. Bonding to zirconia ceramic: adhesion methods and their durability. Dental Materials 1998; 14: 64–71. Kılıçarslan MA, Kedici PS, Küçükeşmen HC, DDS, Uludag BC. In vitro fracture resistance of posterior metal-ceramic and all-ceramic inlay-retained resin- bonded fixed partial dentures. The Journal of Prosthetic Dentistry 2004; 92:365-70. Krejci I, Boretti R, Giezendanner P, Lutz F. Adhesive crowns and fixed partial dentures fabricated of ceromer/FRC: clinical and laboratory procedures. Practical Periodontics and Aesthetic Dentistry 1998; 10:487-98. Krejci I, Duc O, Dietschi D, de Campos E. Marginal adaptation, retention and fracture resistance of adhesive composite restorations on devital teeth with and without posts. Operative Dentistry 2003; 28:127-35. Krejci I, Kuster M, Lutz F. Influence of dentinal fluid and stress on marginal adaptation of resin composites. Journal of Dental Research 1993; 72:490-94. Krejci I, Lutz F, Gautschi L. Wear and marginal adaptation of composite resin inlays. J Prosthet Dent 1994;72:233-44. Krejci I, Lutz F. In-vitro test results of the evaluation of dental restoration systems. Correlation with in-vivo results (in German) Schweizer Monatsschrift fur Zahnmedizin 1990; 100:1445-49. Krejci I, Reich T, Lutz F, Albertoni M. An in vitro test procedure for evaluating dental restoration systems. 1. A computer-controlled mastication simulator (in German) Schweizer Monatsschrift fur Zahnmedizin 1990; 100:953-60. Lassila LVJ, Vallittu PK. The effect of fiber position and polymerization condition on the flexural properties of fiber-reinforced composite. The Journal of Contemporary Dental Practice 2004; 2:014-026. Lassila LVJ, Vallittu PK. The effect of fiber position and polymerization condition on the flexural properties of fiber-reinforced composite. The Journal of Contemporary Dental Practice 2004; 2:014-026. Leal FR, Cobb DS, Denehy GE, Margeas RC. A conservative aesthetic solution

46 for a single anterior edentulous space: case report and one-year follow-up. Practical Procedures & Aesthetic Dentistry 2001; 13:635-41. Loose M, Rosentritt M, Leibrock A, Behr M, Handel G. In vitro study of fracture strength and marginal adaptation of fiber-reinforced-composite versus all ceramic fixed partial dentures. The European Journal of Prosthodontics and Restorative Dentistry 1998; 6:55-62. Lutz F, Göhring TN. Fiber-reinforced inlay fixed partial dentures: maximum preservation of dental hard tissue. Journal of Esthetic Dentistry 2000; 3:164-71. Lutz F, Krejci I, Barbakow f. Quality and durability of marginal adaptation in bonded composite restorations. Dent Mater 1991;7:107-13. Magne P, Perakis N, Belser U, Krejci I. Stress distribution of inlay-anchored adhesive fixed partial dentures: a finite element analysis of the influence of restorative materials and abutment preparation design. The Journal of Prosthetic Dentistry 2002; 87:516-27. Magne P, Versluis A, Douglas WH. Rationalization of incisor shape: experimental-numerical analysis. The Journal of Prosthetic Dentistry 1999; 81:345- 55. Monaco C, Ferrari M, Miceli GP, Scotti R. Clinical evaluation of fiber- reinforced composite inlay FPDs. The International Journal of Prosthodontics 2003; 16:319-25. Murphy J. Reinforced plastics handbook. 2nd ed. Oxford: Elsevier Science; 1998.p. 237-67. Özcan M. The use of chairside silica coating for different dental applications: a clinical report. The Journal of Prosthetic Dentistry 2002; 87:469–72. Perdigão J, Lopes M. Dentin bonding-state of art 1999. The Compendium of Continuing Education in Dentistry 1999; 20:1151-62. Raigrodski A. Contemporary materials and technologies for all-ceramic fixed partial dentures: A review of the literature. The Journal of Prosthetic Dentistry 2004; 92:557-562. Rosentritt M, Behr M, Handel G. Fixed partial dentures: all-ceramics, fibre- reinforced composites and experimental systems. Journal of Oral Rehabilitation 2003; 30:873-77.

47 Tanimoto Y, Nishiwaki T, Nemoto K. Numerical failure of glass-fiber- reinforced composites. Journal of Biomedical Materials Research. 2004; 68A:107- 13. Tinschert J, Natt G, Mautsch W, Augthun M, Spiekermann H. Fracture resistance of lithium disilicate-, alumina-, and zirconia-based three-unit fixed partial dentures: a laboratory study. The International Journal of Prosthodontics 2001; 14:231-38. Valderhaug J. A 15-year clinical evaluation of fixed prosthodontics. Acta Odontologica Scandinavica 1991;49:35-40. Vallittu PK, Sevelius C. Resin-bonded, glass fiber-reinforced composite fixed partial dentures: a clinical study. The Journal of Prosthetic Dentistry 2000; 84:413- 418. Vallittu PK. Prosthodontic treatment with a glass fiber-reinforced resin-bonded fixed partial denture: a clinical report. The Journal of Prosthetic Dentistry 1999; 82:132-35 Vallittu PK. Survival rates of resin-bonded, glass fiber–reinforced composite fixed partial dentures with a mean follow-up of 42 months: A pilot study. The Journal of Prosthetic Dentistry 2004; 91:241-246. Wiedhahn K. Cerec 3 as the first step in digitizing the dental office. International Journal of Computerized Dentistry 2000; 3:67-71. Williams D. Ceramics transformed: manipulating crystal structures to toughen bioceramics. Medical Device Technology 1997; 8:6-8.

48 Chapter 4: Criteria for selecting the materials for IFPDs

49 In case of single missing posterior teeth, the adjacent teeth often contain small occlusal or proximal restorations or initial carious lesions. Conventional porcelain fused to metal fixed partial dentures (FPDs) provide high fracture strength and have a long clinical history (Freilich et al 1998, Pauli 1996). But in most cases full or partial coverage preparations are needed to stabilize the remaining tooth structure and provide sufficient retention. A significant amount of sound tooth structure must be removed when fabricating conventional FPDs (Rammelsberg et al 1995). Fiber-reinforced composites are a new material group with a significantly shorter history of clinical use than more traditional prosthodontic materials. These materials differ in the preparation of their laminates (Behr et al 2000, Behr et al 2001). In posterior areas, however, high mastication forces (approximately 500 to 600 N10) may restrict the use of metal-free IFPDs. The aim of this in vitro study was to examine the fracture strength of metal-free 3-unit posterior IFPDs after aging in an artificial oral environment. One glass fiber–reinforced composites and 2 all-ceramic systems were tested.

Materials and Methods

The previously eighteen inlay bridges made using three different materials with unlike flexural strengths and Young’s moduli were loaded until the fracture after the fatigue machine. FRC (SR Adoro/Vectris; Ivoclar/Vivadent), zirconium oxide-TZP “tetragonal zirconia polycrystals” (Cercon, DeguDent; Dentsply) and magnesia- partially stabilized zirconia (DC-Leolux; DCS Dental, Allschwil) covered with silica- based ceramics were tested in this study. The fracture strength of each IFPD was determined by mechanically loading them to failure with a universal testing machine (Instron) after the aforementioned artificial aging. The force was applied on the center of the pontics using a steel ball (6 mm diameter, 1 mm/minute crosshead speed). To ensure regular force distribution and minimize the transmission of local force peaks from the steel ball to the cusps of the pontics, a layer of tin foil (0.5 mm) was inserted. The failure determination was set at a 10% loss of the maximum loading force. Radiologic examinations (X-ray, Castellini, Italy) were made to document the different fracture patterns. Median standard deviation values were calculated for all groups. The statistical analysis was performed using the Mann-

50 Whitney U test and the Kruskal- Wallis test for nonnormal distributed values (JMP 5.1). The level of significance was set to p =0.05.

Results

All fracture strength results are shown in Figures 1-2. The results for all samples are given in Table 1. The values for FRC Adoro/Vectris system was 1382N (1172N 25% percentile, 1549N 75% percentile), for DSC DC-Leolux 1433N (1239N 25% percentile, 1570N 75% percentile), and for Cercon system was 1695N (1538N 25% percentile, 1814N 75% percentile). There was no statistical difference between FRC and DC-Leolux, and DC-Leolux and the Cercon system. In contrast, there was a statistical difference between the FRC group and the Cercon system. Fig. 3 shows a representative pattern of fracture for a fiber-reinforced composite IFPD. The failure of the IFPDs can be attributed to either fractures of the facing material or shearing of the facing material from the framework fibers. No discernible damage to the framework fibers was observed. Fig 4 shows the characteristic failure pattern of an allceramic IFPD. The fractures occurred mainly at the connectors between the pontic and the abutment in combination with a complete fracture of the restoration.

Table. Results for all samples FRC DC-Leolux Cercon 1 1613 1789 1846 2 1528 1497 1804 3 1467 1440 1744 4 1297 1426 1646 5 1177 1278 1580 6 1160 1123 1413 Total 1373,7 1425,5 1672,2 Standard deviation 189,7 223,9 160,7

51 FRC DCS

2000 1800

1600 1500 1400

1200 1000 1000

800

500 600

400 0 200 123456 0 123456 FRC 1613 1528 1467,7 1297 1177 1160 DCS 1789 1497 1440 1426 1278 1123 a b Fig. 1-a-b. The graphs a, b showes the values of the FRC and DSC groups.

CERCON

2000

1500

1000

500

0 123456

CERCON 1846 1804 1744 1646 1580 1413 a Fig. 2. The graph a shows the value of the Cercon group for all samples.

1900

1800

1700

1600 1

1500 Column

1400

1300

1200

1100 Cercon DC-Leolux FRC Fig. 3. The graph a shows the comparition of the all groups.

52 Discussion The examination methods used for testing fracture strength follow established procedures previously described in the literature ( Pauli 1996, Behr et al 2000, Behr et al 2001). The artificial oral environment allowed for the simulation of parameters such as temperature changes, mastication force, frequency of occlusal loads, and resiliency of the human periodontium (Krejci et al 1990). The advantage of this system is the application of similar conditions on each specimen. This system can be used for aging dental restorations in vitro to estimate mechanical properties of new dental materials before any timeconsuming and large-scale clinical investigations are undertaken (Rosentritt et al 1997, Delong et al 1983). Assuming maximum mastication forces of about 500 N (Hidaka et al 1999) in posterior chewing areas, the results found in this study were within the range for the fiber-reinforced systems (Adoro/Vectris) and for the all-ceramic system (DC-Leolux, Cercon). The results for the Adoro/Vectris IFPD are increased to those found in a vitro study conducted by Behr (Behr et al 1999) comparing tub-shaped and box-shaped preparation techniques with Targis/Vectris. In this study the framework were composed only of the pontic prepreg fibers and showed fracture strength values of 696 N (531 N/958 N) in the box-shaped preparation and 722 N (665 N/818 N) in the tub-shaped preparation. The Vectris framework consists of 3 different prepregs that can be distinguished by the fiber orientation; prepregs with parallel fibers are called “pontic,” those with a 45-degree alignment are called “single,” and those with a 90- degree alignment are the “frame” prepregs. Kolbeck (Kolbeck et al 2002) investigated with the Targis/vectris system a combination of pontic prepreg and single prepreg fibers and showed nearly exactly the same fracture strength than those without the single prepreg [723 N (692N/806 N)]. Thus, one might interpret that for Vectris/Targis IFPDs, it is more important to prepare a tub-shaped cavity without sharp inner edges rather than to use a large quantity of different prepreg fibers. A disadvantage of the tub-shaped cavity might be the greater potential for pulp irritation or exposure. In any cases, the value for the FRC group was lower than 1000N and rather near to the threshold of the 500N. The laboratory technique used in our study allows the extension in the vestibular and buccal side to support the layering material like in metal framework and hold it in all loading directions. The framework in the FRC was made in an anatomical shape in the pontic element with

53 parallel and weave fiberglasses. Vestibular and buccal FRC extensions in the pontic element can increase the bonding area between the framework and resin composite as well as hold the veneer material better during occlusal loading. This observation suggested that modified design of frameworks could increase the bond strength of resin composite to the fiber framework when chewing (Monaco et al 2003). The fiber-reinforced materials have higher bending tendencies because of their lower modulus compared to the more brittle ceramic material, but when the ceramic material is supported by the zirconia framework the values can widely increase above the threshold of the 500N. The ceramic fractures occur at the connectors between pontic and abutment, where embrasure contours are critical. It should be kept in mind that all of the results reported herein are from an in vitro study. Clinical conditions may be more critical than those simulated in vitro and potentially may result in lower forces creating failure. Despite of these potential limitations, however, the results of this study support further investigation, and the clinical application of these materials seems possible and promising.

References

Freilich MA, Karmaker AC, Burstone CJ, et al: Development and clinical applications of a light-polymerized fiber reinforcedcomposite. J Prosthet Dent 1998;80:311-318 Pauli C: Fracture strength of ceramometal and all-ceramic posterior fixed partial dentures. ZWR 1996;11:626-632 Rammelsberg P, Behr M, Pospiech P, et al: Adhesively fixed partial dentures: Esthetic and substance preserving alternatives for conventional fixed partial dentures. DZZ 1995;50: 224-227 Behr M, Rosentritt M, Lang R, et al: Flexural properties of fiber reinforced composite using a vacuum/pressure or a manual adaptation manufacturing process. J Dent 2000;28: 509-514. Behr M, Rosentritt M, Latzel D, et al: Comparison of three types of fiber- reinforced composite molar crowns on their fracture resistance and marginal adaptation. J Dent 2001;29:187-196 Krejci I, Reich T, Lutz F, et al: In vitro test results of the evaluation of dental restoration systems. Correlation with in vivo results. Schweiz Monatsschr Zahnmed 1990;100:1445-1449. Rosentritt M, Leibrock A, Lang R, et al: Regensburger masticator. Mater Test 1997;39:77-80 Delong R, Douglas WH: Development of an artificial oral environment for the testing of dental restoratives: Bi-axial force and movement control. J Dent Res 1983;62:32-36

54 Hidaka O, Iwasaki M, Saito M, et al: Influence of clenching intensity on bite force balance, occlusal contact area and average bite pressure. J Dent Res 1999;78:1336-1344. Behr M, Rosentritt M, Leibrock A, et al: In vitro study of fracture strength and marginal adaptation of fiber-reinforced adhesive fixed partial inlay dentures. J Dent 1999;27:163-168. Monaco C, Ferrari F, DDS, Miceli GP, Scotti R. Clinical Evaluation of Fiber- Reinforced Composite Inlay Fixed Partial Dentures. Int J Prosthodont 2003;16:319- 325.

55 Chapter 5: laboratory process for high volume fiber framework

Missing single-tooth situations offer several reconstructive treatments modalities. Adhesive bonded restorations made with fiber-reinforced composite (FRC) have been proposed for the fabrication of metal-free inlay fixed partial dentures (IFPDs). Nevertheless, for a small sized construction, such as a dental prosthesis, the design and characteristics of the fiber framework are important and demand careful attention. Fiber reinforcement should be optimal when the designing of the prostheses and their components need to be realized to withstand masticatory loading. This technical procedure describes the way to realize the cusp-supporting framework with high volume of fibers and completely support the layering material.

56 The IFPD is indicated in all clinical cases were the replacement of a single tooth is required but treatment with a dental implant cannot be realized. In this situation, an inlay bridge offers a more conservative method of tooth replacement compared to a crown retained conventional bridge because tooth preparations are limited to the occluso and mesio/distal surfaces of abutment (Fig.1). However these preparations are more clinical sensitive technique and required a careful laboratory procedure (Monaco et al 2003). The cavity preparation must give the space to the fiber framework that must completely support the pontic element. Freilich (Freilich at al 2002) hypothesized the increased rigidity and a broader base of support provided by the FRC substructure was needed to support the composite veneer. Thus, they added a substantial amount of FRC bulk to the pontic component of the substructure (low- volume design), resulting in the creation of the “high-volume” substructure design and examined their relationship with the clinical performance. This technical procedure describes the realization of the fiber framework with an anatomical shape and high volume of fibers that allows the extension of the pontic element to support the layering material. The final design of the bridge’s framework is similar to metal framework with extensions in the vestibular and buccal side to completely hold up the veneer composite and avoid the cohesive fracture of the composite.

Laboratory Technique The glass fiber framework (Vectris; Ivoclar Vivadent) is made with pre-impregnated ‘pontic’ and ‘frame’ fibers with a monomer consisting of dimethacrylates and the final sub-structure has an anatomical shape of the framework and a high volume of the glass fibers. The design of the fiberglass framework is first pre-modeled by a photo-curing resin (Spectra Tray, Ivoclar Vivadent) to obtain the oval shape and its thickness is checked in the molding model. The dental technician must empty the space for the veneering material and check with carefulness the space of the connector surface. This area must be minimum 9mm2 (3x3m), otherwise the flexibility of the framework could increase and determine the worsening of the marginal adaptation. The photo-curing resin framework is embedded in a transparent silicone impression paste to form a mould. Then the resin model is removed and the glass fibers are inserted into the

57 silicone-mould. The pre-impregnated pontic fibers are condensed into the desired shape by a vacuum- forming process and then cured by light in a VS1 unit (Ivoclar Vivadent) for 10 min. According to the manufacturer’s recommendations, the pontic fibers are treated with silane to increase the bonding to the following fiber layer. A sheet of weave fibers (frame) is placed upon the pontic structure and the cycle in VS1 is repeated. After the moulding of the sheet fibers all excesses are removed with a carbide bur and the framework is tried on the master model (Fig. 2). The veneering material is built incrementally using a Quick light-curing unit. Finally, the IFPD is placed into a Lumamat 100 unit (Ivoclar Vivadent) for the final application of light and heat (104°C) to complete polymerization and maximize strength and other physical characteristics (Fig. 3). After the polishing the IDPD is ready for the luting procedures (Fig. 4).

Discussion Many FRC researches on position and orientation have focused upon the effects of the question of fiber reinforcement directionality like random, longitudinal orientations or weaved. It is widely accepted that directional orientation of the fiber long axis perpendicular to an applied force will result in strength reinforcement. Forces that are parallel to the long axis of the fibers, however, produce matrix- dominated failures and consequently yield little actual reinforcement. Design strategies are on occasion employed to provide multi-directional reinforcement, to minimize the highly anisotropic behavior of unidirectional fiber reinforcement ( Dyer et al 2004). A higher volume fraction of fibers in the resin matrix improves the mechanical properties. Moreover, the flexibility of the beam is in direct relation to the amount, position and the type of the fibers that go to make up the framework. The position of the FRC layer had an effect on the flexural strength of the framework. The highest flexural strength was achieved when the FRC layer was located at the tension side of the test specimens. The FRC structure benefits most when the tensile stresses can be transferred to the reinforcing fibers (Vallittu 1998). This laboratory technique allows the extension in the vestibular and buccal side to support the veneering material like in metal or zirconia frameworks and hold it in all loading directions. Vestibular and buccal FRC extensions in the pontic element can

58 increase the bonding area between the framework and resin composite as well as hold the veneer material better during occlusal loading.

Conclusion The design of the FRC framework can play an important role in supporting the layering material in order to optimize the position and orientation of fibers that should maximize the stress transferred from matrix to fibers and increase mechanical properties of IFPDs.

Fig. 1 The presence of old restorations Fig. 2 The anatomical fiber framework is on the abutments near the edentulous designed to completely support the space is the typical situation for the veneering composite and increase the IFPDs mechanical properties of the IFPD.

Fig. 3 . IFPD made with fiber reinforced Fig.4 Follow-up after 2 years. composite.

References

Dyer SR, Lassila LVJ, Jokinen M, Vallittu PK. Effect of fiber position and orientation on fracture load of fiber-reinforced composite. Dent Mater 2004;20: 947–955. Freilich MA, Meiers JC, Duncan JP, Eckrote KA, Goldberg AJ. Clinical evaluation of fiber-reinforced fixed bridges. J Am Dent Assoc 2002;133:1524- 1534. Monaco C, Ferrari F, DDS, Miceli GP, Scotti R. Clinical Evaluation of Fiber-

59 Reinforced Composite Inlay Fixed Partial Dentures. Int J Prosthodont 2003;16:319- 325. Vallittu PK. Some aspects of the tensile strength of undirectional glass fibre- polymethyl methacrylate composite used in dentures. J Oral Rehabil. 1998 Feb;25(2):100-5.

60 Chapter 6: Different structure of the framework

The traditional treatment for a single tooth replacement is a conventional fixed partial denture (FPD). This technique requires a full-coverage preparation of the abutments. Consequently, a large quantity of sound tooth is destroyed during the preparation (Creugers et al 2000). This is particularly problematic in healthy and young teeth with extensive pulp. In addition, the mean of a FPD is estimated at 8.3-10.3 years (Creugers et al 2000, Näpänkangas et al 2002). Furthermore, a young patient would require numerous replacements of this restoration over a lifetime. In order to limit this destruction and thanks to evolution of adhesive dentistry, (Perdigão et al 1999) resin bonded fixed partial dentures (RBFPDs) (Freilich et al 1998) and dental implants (Leal et al 2001) constitute the current alternatives. These treatments have several advantages over conventional bridges, especially in relation to conservation of tooth structure and their reversibility (Hussey et al 1996). Nevertheless, published data on the survival of RBFPDs with metal framework are still controversial. Some study reports that resin-bonded bridges placed in the posterior region were less retentive that FPDs placed in the anterior region (Creugers et al 1997, Creugers et al 1992). De Kanter (De Kanter et al 1998) reported only 46% and 62% of primary survival rates at 5 years of RBFPDs respectively for conventional and modified preparation forms. A multi-centers study (Kerschbaum et al 1996) reported a success rate of 66% that increased to 82% with additional rebonding. However, tooth-colored framework and a metal-free prosthetic reconstruction cannot be built with this technique. Consequently, alternative materials such as high-strength pressed ceramic (Sorensen et al 1999) and fiber-reinforced composites (FRC) have achieved (Freilich et al 1998) a certain degree of popularity in restorative dentistry today. Various types of fibers such as carbon fiber, aramid fiber and ultra-high modulus polyethylene fiber have been tested (Ekstrand et al 1987, Gutterridge 1992, Uzun et al 1999, Larson et al 1991, Hess et al 1987) as reinforcing materials, and it has been shown that the fibers also increase the elastic modulus and flexural strength of dental polymer. Recently, glass fibers have been used to reinforce denture base polymers (Krause et al 1989). Glass fibers are favorable for denture base polymer

61 when used in light curing type resin because they have excellent transparency compared to the other fibers (Vallittu 1999a). The advantages of FRC restorations are that the laboratory procedure is simple because casting is not necessary, and the bonding ability between resin and reinforced fiber is superior to that between resin and casting metal, although surface treatment of fiber is necessary to obtain a strong bonding (Vallittu 1999b). Reinforcement of dental resins with short or long fibers has shown positive results and, generally, better mechanical properties when compared to metal wires in polymers reinforcement (Vallittu 1996c). A glass FRC system made of prefabricated glass fiber elements along with processing and curing equipment (Targis-Vectris, Ivoclar-Vivadent) was introduced in 1996 (Krejci et al 1998). A recent in vitro study reported high fracture strength of 700 N of fiber-reinforced adhesive IFPDs. With one exception, the break always ran along the interface between fiber-composite or in the Targis material itself (Behr et al 1999). The framework in the FRC is supposed to be made in an oval shape in the pontic element with parallel and weave fiberglasses. This laboratory technique allows the extension in the vestibular and buccal side to support the layering material like in metal framework and hold it in a continuous manner. In the present study, the frameworks was made with different uses and shapes of the fiberglasses to investigate the clinical behavior of IFPDs. The purpose of this study was to collect survival data on posterior IFPDs, which were placed under controlled clinical conditions and to identify the correlation between the design of fiber frameworks and survival of IFPDs.

Materials and methods Thirty patients were selected and received an indirect restoration. The selection of the patients followed two criteria: their refusal to treatment with dental implants and informed written consent. Selection of male and female subjects was restricted to those aged 18-60 years and in good general and periodontal health. Patients with the following factors were excluded from the clinical trial: patients receiving drugs that modify pain perception, pregnancy or breast feeding, eating disorders, periodontal surgery, well-known allergy to chemical compounds used in this study and active periodontal disease.

62 From January 1998 to January 2002 forty-one IFPDs were inserted. Average service time of Targis-Vectris was 27.2 months. Twenty-four restorations were placed in mandibular teeth and 17 in maxillary teeth and evaluated using the USPHS criteria. According to the manufacturer’s instructions the Vectris frameworks in the IFPDs are made with pre-impregnated ‘pontic’ and ‘frame’ fibers (Ivoclar: Scientific Document 1996). The FRC framework was made with only pontic fiber in nineteen restorations (Group 1) and with pontic and frame pre-impregnated fiberglass in twenty-two restorations (Group 2) according to the manufacturer’s instructions. In the Group 1 the design of pontic element was made in a cylindrical shape whereas in the Group 2 was modified in oval shape to hold the layering material in a continuous manner (Fig 1). The final shape of Group 2 was similar to metal framework with extensions in the vestibular and buccal side to support completely the veneer composite.

Clinical Preparation Technique At baseline all patients were tested for dentin sensitivity. In the rank order data, a score of 0 was defined as no pain, 1-4 as mild sensitivity, which was provoked by the dentists’ air blast, and 5-10 as strong sensitivity, which was spontaneously reported by the patient during drinking or eating. The same measurement was performed again at each recall. The status of the gingival tissues adjacent to the test sites was observed at baseline and each recall. Before cavity preparation a rubber dam was placed and all cavities were prepared according to modified principles for adhesive inlays retainers to obtain adequately strong dental restorations. No additional bonding FRC wings were made to obtain more adhesional surface. The cavities were prepared with 80µm (No. 8113R, No. 8113NR, Intensiv SA) and finished with 25µm (No. 3113R, No. 3117, Intensiv SA) diamond burs in a medium-speed handpiece with a water spray. All the dentin surfaces of the cavity preparations were sealed with a three-component enamel- dentin adhesive system (Syntac, Ivoclar-Vivadent). Undercuts and deep parts of the cavities were covered with a resin composite (Tetric ceram, Ivoclar-Vivadent) polymerized for 40 sec. All cavity margins were in enamel and extrasulcus. The distance to marginal gingival was at least 1 mm. Complete mandibular and maxillary

63 arch impressions were taken with a polyvinyl siloxane (Imprint II, 3M ESPE). A light-cured resin (Fermit-N, Ivoclar-Vivadent) was used as temporary restoration.

Laboratory Technique The design of the fiberglass framework was first pre-modeled by a photo-curing resin (Spectra Tray, Ivoclar) to obtain the oval shape and its thickness checked onto the molding model. This model was embedded in a transparent silicone impression paste to form a mould. Then this resin was removed and the fibers were applied into the silicone-mould (Fig 2). The pre-impregnated ‘pontic’ fibers were condensed in a deep-drawing, polymerization process. After a cycle of vacuum packing and heat in VS1 unit (Ivoclar-Vivadent) for 9.30 min. according to the manufacturer’s recommendations, the FRC was sandblasted with CoJet system (3M ESPE) with small grain size of 30 m at 2,5 bar of pressure for 10 seconds or roughened with 8o m diamond bur and treated with silane (Wetting agent, Ivoclar-Vivadent). A sheet of wave fibers ‘frame’ was placed upon the ‘pontic’ structure and the cycle in VS1 was repeated. The Targis material was built incrementally using Targis Quick. Finally, the IFPD was placed into the Targis Power unit (Ivoclar-Vivadent) for the final application of light and heat to complete polymerization and maximize strength and other physical characteristics.

64 the cementing step. The restorations were then finished with 15µ m diamond burs (Composhape, Intensiv) and polished with a composite finishing and polishing kit (Hawe Neos Dental) and Occlubrush (Hawe Neos Dental) in a slow-speed handpiece.

Evaluation One investigator evaluated all the restorations directly after the final polishing (Fig 4) and after 6, 12, 24 and 48 months. During the recalls, the patients came back to the office to answer questions about post-operative sensitivity. Partial or total debonding of IFPDs and framework or resin composite fractures were considered failures. Patients with failure were examinated immediately to verify the assumption and the precise time of the failure. The restorations were evaluated, using the USPHS modified parameters, to check their stability and longevity in regard to the following characteristics: color match, marginal discoloration, secondary caries, surface texture, marginal adaptation, fracture and postoperative sensitivity. The scores were Alfa (ideal), Bravo (clinically acceptable), Charlie (clinically unacceptable) scores.

Statistical Analysis Statistical analysis was applied to compare the restorations at baseline and after last recall, and to check for differences between Group 1 and 2. The Wilcoxon’s matched-pairs signed ranks test and McNemar test measured the restorations’ success at the appropriate time intervals and were used to rate all parameters. The Chi-square test was used to examine for a significant difference in fracture rate between IFPDs with conventional fiber framework structure and those with modified. The null hypothesis was rejected at the 5% level. The survival estimation method of Kaplan- Maier was used with statistical software (Primer 4.02, Stanton A. Glantz, McGraw- Hill).

Results No partial/total debonding of the IFPDs or breakage of fiber frameworks were shown during the observation period. Three partial adhesional/cohesional veneering composite fractures (Fig 5) occurred in the occlusal-buccal side of the pontic element in Group 1 after 3, 4 and 8 months. Intraoral repairs were made in all cases of

65 breakage and two IFPDs were completely replaced after a few weeks because the composite repairs had debonded. After each failure, the fiber framework was visible at low magnification (Zeiss 3.6x35mm). One cohesive fracture of Targis (Fig 6) occurred in the abutment in Group 2 after 46 months. The FPD was repaired after two weeks of intraoral exposion and it is still in place. No statistical differences regarding fractures were showed between baseline and last recall and between Group 1 and 2 (P>0.05). The percentage of Bravo color match for the IFPDs increased from 7% at baseline to 29% at last recall with statistically significant difference (P<0.048). The small changes noted during the follow-up period in clinical results for the abutments were not statistically significant (Table 1). Four patients reported postoperative hypersensitivity. These patients reported temperature sensitivity and chewing pain for periods lasting from 1 week to 2 months. These complaints disappeared completely within 6 months. The Kaplan-Maier survival estimation was 86% for Group 1 and Group 2 (Fig 7). Table 1 Clinical Results Based on USPHS Criteria

Baseline Last Recall Baseline Last Recall % Alfa at

Abutments (n=82) Alfa Alfa Bravo Bravo Last

Recall

Marginal discoloration 82 79 0 3 96

Secondary caries 82 81 0 1 99

Marginal adaptation 82 80 0 2 98

Postoperative sensibility 78 82 4 0 100

IFPDs (n=41)

Fracture 41 37 0 4 90

Surface texture 41 36 0 5 88

Color match 38 29 3 12 71

Discussion Inlay fixed partial dentures with fiber framework offer a new option to restore a missing tooth with a less invasive method and with better esthetic treatment than with

66 metal FPDs. Data on the clinical performance of FRC is needed to estimate the survival rates as well as to gain knowledge on the appropriate use of fibers in combination with resin composites. There are few clinical studies on the behavior of FPDs and most of them are short-term evaluations (Göhring et al 1999, Vallittu et al 2000, Lutz et al 2000). One of the advantages of IFPDs is their intraoral repairing (Swift et al 1992) but post light curing and heat treatment determine a high degree of conversion. This treatment improves mechanical properties but it makes the repair of IFPDs more difficult. In our study, all adhesional/cohesional veneering composite fractures occurred in the pontic element in Group 1. Similar failures were reported in an earlier experimental study with fiber-reinforced composite using a laboratory multistep (Altieri et al 1994). Two of the three intraoral repairs failed after 2 weeks. There are a few plausible explanations for the failures. First, the design of the FRC framework can play important role in supporting the layering material in a continuous manner. Vestibular and buccal FRC extensions in the pontic element can increase the bonding area between the framework and resin composite as well as hold the veneer material better during occlusal loading. Failure was invariably seen in the same position in all bridges with conventional framework design. This observation suggested that modified design of frameworks could increase the bond strength of resin composite to the fiber framework when chewing. Continuous unidirectional fibers gave the highest strength and stiffness only in the direction of the fiber. Woven fibers are able to reinforce the denture base polymers in two directions (DeBoer et al 1984). However, definitive recommendations for prostheses manufacturing currently cannot be made. Further in vitro and clinical studies must be conducted to confirm this hypothesis. Second, there might have been inadequate bonding between fiber framework and composite especially after repair. Rosentritt (Rosentritt et al 1998) demonstrated that median facing fracture strength of Targis/Vectris bridges was 1450 N after a simulated clinical service of 5 years but the fracture strengths of the repair IFPDs were significantly lower compared with the control group after an additional simulated 2-year interval. However, the median fracture force was still 1000 N higher than chewing force. Dynamic tests would have different value in comparison to the static tests. Furthermore, they showed that aluminum oxide pretreatment or

67 abrading with diamond burs and silanization provided in vitro sufficient fracture strength. Nevertheless, an aqueous environment can induce corrosive effects on the surface of glass fibers resulting from water absorption through the polymer matrix (Lassila et al 2002). Other substances, like alcohol, can break the polymer chains with a softening effect on the composite that can lead to a reduction of the mechanical strength (Ehrenstein et al 1990). The bonding values between a repair and an aged framework are about 20% to 70% lower in comparison to the bonding between a new framework and veneer (Swift et al 1994). Therefore, the design of the IFPD after repair should help to preserve points of high stress, especially in occlusal areas. Third, it is possible that cohesional fractures inside resin composite may be caused by air entrapment during manufacturing to ensure esthetics. Entrapment of air locally inhibits polymerization and weakens the structure of materials (Vallittu et al 1997). Görhing (Görhing et al 1999) described a modified manufacturing technique to eliminate occlusal multilayering and to reduce the risk of veneering composite fractures. The matrix chemistry of the repair composite might not influence the repair strength (Gregory et al 1990), but the composite should provide low viscosity to achieve a good wetting of the repair point (Rosentritt et al 1997). The moderate decrease in fracture resistance obtained after veneering repair in vitro of Targis/Vectris bridges indicates that repeated repair is possible (Rosentritt et al 2001), although it is highly risky to repair an extremely damaged FPD that has lost more than 50% of the veneer substance. The percentage of bravo in color match was 29% at last recall and the deterioration was significant compared to initial status. Some inlay FPDs lost their surface shine with the color that was slightly too dark/opaque with superficial stains and the repolishing was only partially successful in reversing the discoloration. Color changes or resin material can occur through several mechanisms: formation of degradation products changes in surface structure due to the wear and by extrinsic staining (Powers et al 1980). Douglas (Douglas 2000) showed that after accelerated aging the new generation of indirect resins demonstrated color changes at or below a quantitative level that would be considered acceptable. These changes were in the magnitude of 0.62 to 3.4 E units. However, Stober (Stober et al 2001) described changes in color of the same composite after 4 and 8 week storage in various

68 substances generally thought to cause intra-oral discoloration. In particular, red wine and turmeric solution caused severe discoloration with total differences of ∆E >10 in all tested composites. It is apparent from our results that it remains essential to improve the color stability of Targis material used for esthetic facing. In a short-term observation period, the FRC showed good clinical service but these results need more observation in order to create a sound basis for the final assessment of this method. In our study the veneering composite had less fractures with modified FRC frameworks than with the conventional design. Based on our observations the repair of FRC fractured veneer is advisable only for small damages.

References

Altieri JV, Burtone CJ, Goldberg AJ, Patel AP. Longitudinal clinical evaluation of fiber-reinforced composite FPDs: a pilot study: J Prosthet Dent 1994;71:16-22.

Behr M, Rosentritt M, Leibrock A, Schneider-Feyrer S, Handel G. In vitro-study of fracture strength and marginal adaptation of fibre-reinforced adhesive fixed partial inlay dentures. J Dent 1999;27:163-168.

Creugers NH, De Kanter RJ, Van’t Hof MA. Long-term survival data from a clinical trial on resin bonded bridges. J Dent 1997;25:239-242.

Creugers NH, Käyser AF, Van’t Hof MA. A seven-and-half–year survival study of resin-bonded bridges. J Dent Res 1992;71:1822-1825.

Creugers NHJ, De Kanter RJ. Patients’ satisfaction in two long-term clinical studies on resin-bonded bridges. J Oral Rehabil 2000;27:602-607.

Creugers NHJ, Käyser AF, Van’t Hof MA. A meta-analysis of durability data on conventional fixed bridges: Community Dent and Oral Epidemiol 1994; 22:448-452.

De Kanter RJ, Creugers NH,Verzijden CW, Van’t Hof MA. A five-year multi- practice clinical study on posterior resin-bonded bridges. J Dent Res 1998;77:609- 614.

DeBoer J, Vermilyea SG, Brady RE. The effect of carbon fiber orientation on the fatigue resistance and bending properties of two denture resins. J Prosthet Dent 1984;51:119-121.

69 Douglas DR. Color stability of new-generation indirect resins for prosthodontics application. J Prosthet Dent 2000;83:166-170.

Ehrenstein GW, Schmiemann A, Bledzki A, Spaude R. Corrosion phenomena in glass-fiber-reinforced thermosetting resins. In: Cheremisinoff NP (ed). Handbook of ceramics and composites, vol 1. New York: Marcel Dekker, 1990:231-268.

Ekstrand K, Ruyter IE. Carbon/graphite fiber reinforced poly(methyl methacrylate): properties under dry and wet conditions. J Biomed Mater Res 1987;21:1065-1080.

Freilich MA, Duncan JP, Meiers JC, Goldberg AJ. Preimpregnated, fiber- reinforced prostheses. Part I: basic rationale and complete coverage and intracoronal fixed partial denture designes. Quintessence Int 1998;29:689-696.

Freilich MA, Duncan JP, Meiers JC. Preimpregnated, fiber-reinforced prostheses. Part I. Basic rationale and complete-coverage and intracoronal fixed partial denture designs. Quintessence Int 1998:29:689-696.

Göhring TN, Krejci I, Lutz F. Adhäsive Inlaybrücken aus glasfaserverstärktem Komposit. Step by step-Beschreibung der klinischen Anwendung. Schweiz Monatsschr Zahnmed 1999;109:369-379.

Göhring TN, Mörmann WH, Lutz F. Clinical and scanning electron microscopic evaluation of fiber-reinforced inlay fixed partial dentures: Preliminary results after one year. J Prosthet Dent 1999;82:662-668.

Gregory DC, Pounder B, Bakus E. Bond strengths of chemically dissimilar repaired composite resins. J Prosthet Dent 1990;64:664-668.

Gutterridge DL. Reinforcement of poly(methyl methacrylate) with ultra-high- modulus polyethylene fiber. J Dent 1992;20:50-54.

Hess D, Belser U. Provisional extension bridges reinforced with Kevlar. Schweiz Monatsschr Zahnmed 1987;97:457-463.

Hussey DL, Linden GJ. The clinical performance of cantilevered resin-bonded bridgework. J Dent 1996;24:251-256.

Ivoclar: Scientific Document. Ivoclar-Vivadent, Schaan, FL, 1996.

Kerschbaum T, Haastert B, Marinello CP. Risk of debonding in three-unit resin- bonded fixed partial dentures. J Prosthet Dent 1996;75:248-253.

Krause WR, Park SH, Straup RA. Mechanical properties of BIS-GMA resin short glass fiber composites. J Biomed Mat Res 1989;23:1195-1211.

Krejci I,Boretti R, Giezendanner P, Lutz F. Adhesive crowns and fixed partial dentures fabricated of ceromer/FRC: clinical and laboratory procedures Pract

70 Periodont Aesthet Dent 1998;10:487-498.

Larson WR, Dixon DL, Aquilino SA, Clancy JM. The effect of carbon graphite fiber reinforcement on the strength of provisional crown and fixed partial denture resins. J Prosthet Dent 1991;66:816-20.

Lassila LVJ, Nohrström T, Vallittu K. The influence of short term water storage on the flexural properties of unidirectional glass fiber-reinforced composite. Biomaterials 2002;23:2221-2229.

Leal FR, Cobb DS, Denehy GE, Margeas RC. A conservative aesthetic solution for a single anterior edentulous space: case report and one-year follow-up. Pract Proced Aesthet Dent 2001;13:635-641.

Lutz F, Göhring TN. Fiber-reinforced inlay fixed partial dentures: maximum preservation of dental hard tissue. J Esthet Dent 2000;12:164-171.

Näpänkangas R, Salonen-Kemppi MAM, Raustia AM. Longevity of fixed metal ceramic bridge prostheses: a clinical follow-up study. J Oral Rehabil 2002;29:140- 145.

Perdigão J, Lopes M. Dentin bonding-state of art 1999. Compend Contin Educ Dent 1999;20:1151-1162.

Powers JM, Fan PL, Raptis CN. Color stability of a new composite restorative material under accelerated aging. J Dent Res 1980;59:2071.2074.

Rosentritt M, Behr M, Kolbeck C, Handel G. In vitro repair of three-unit fiber- reinforced composite FPDs. Int J Prosthodont 2001;14:344-349.

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Sorensen JA, Cruz M, Mito WT, Raffeiner O, Meredith HR. Foser HP. A clinical investigation on three-unit fixed partial dentures fabricated with lithium disilicate glass-ceramic. Pract Periodontics Aesthet Dent 1999;11:95-106.

Stober T, Gilde H, Lenz P. Color stability of highly filled composite resin materials for facings. Dent Mater 2001;17:87-94. Swift EJ, Le Valley BD, Boyer DB. Evaluation of new methods for composite repair. Dent Mater 1992 ;8:362-5.

Swift, EJ, Bryan CC, Boyer DB. Effect of silane coupling agent on composite repair strengths. Am J Dent 1994;7:200-202.

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71 impact and transverse strength of a denture base resin. J Prosthet Dent 1999;81:616- 620.

Vallittu PK, Sevelius C. Resin-bonded, glass fiber-reinforced composite fixed partial dentures: a clinical study. J Prosthet Dent 2000; 84:413-418.

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72 Chapter 7: adhesive procedures 7.1 Inlay Bridge With a New Microfilled Composite: A Clinical Report

73 The traditional treatment for a single tooth replacement is a conventional fixed partial denture (FPD). This technique requires a full-coverage preparation of the abutments. Consequently, a large quantity of sound tooth is destroyed during the preparation (Creugers et al 2000). This is particularly problematic in healthy and young teeth with extensive pulp. In addition, the mean of a FPD is estimated at 8.3- 10.3 years (Creugers et al 1994, Näpänkangas et al 2002). Thanks to evolution of adhesive dentistry (Perdigão 1999) this destruction can be limited. Resin bonded fixed partial dentures (RBFPDs) (Freilich et al 1998) and dental implants (Leal et al 2001) constitute the current alternatives. These treatments have several advantages over conventional bridges, especially in relation to conservation of tooth structure and their reversibility (Hussey et al 1996). Fiber-reinforced composites (FRC) have achieved (Freilich 1998) a certain degree of popularity in restorative dentistry today (Vallittu 1999a). Glass fibers are favorable for denture base polymer when used in light curing type resin because they have excellent transparency compared to the other fibers. The advantages of FRC restorations are that the laboratory procedure is simple because casting is not necessary, and the bonding ability between resin and reinforced fiber is superior to that between resin and casting metal, although surface treatment of fiber is necessary to obtain a strong bonding (Vallittu 1999b). A novel type of composite material (SR Adoro; Ivoclar Vivadent) has been recently introduced for dental use. One advantage of this new material is the ability to form good bonding with the polymer matrix of the glass fiber system (Vectris; Ivoclar Vivadent) and the luting composite.

This clinical report describes the treatment of a patient with a missing lower first molar with a new microfilled composite supported with a glass fiber framework.

Inlay Bridge indication

The inlay bridge is indicated in all clinical cases were the replacement of a single tooth is required but treatment with a dental implant cannot be realized. In the following situations treatment with implants may not be possible: patient rejects surgical treatment, costs of implant therapy are too high, not enough bone remaining

74 for the placement of an implant, poor prognosis of implant therapy due to patient related situations, e.g., smoking and insufficient oral hygiene habits. In this situation, an inlay bridge offers a more conservative method of tooth replacement compared to a crown retained conventional bridge because tooth preparations are limited to the occluso and mesio/distal surfaces of abutment. However these preparations are more technique sensitive and required a careful adhesive luting procedure. Short spans, not exceeding 10-12 mm (the space of a molar) are recommended and the preparation must give the space to the fiber framework to support completely the pontic element.

Clinical Report A 35-year-old woman presented herself in the Department of Prosthetic Dentistry of University of Bologna for the replacement of the first lower molar. The patient was previously treated by her dentist with implant technique without success and was not willing to have another surgical treatment because of the additional expense.

Intraoral examination revealed the presence of OD composite restoration on the second premolar and an amalgam filling with a medium decay on the second molar. The patient opted for a treatment with a conservative glass fiber composite RBFPD.

Clinical Preparation Technique

Before cavity preparation a rubber dam was placed and the cavities were prepared according to modified principles for adhesive inlays retainers to obtain adequately strong dental restorations.

No additional bonding FRC wings were made to obtain more bonding surface. The cavities were prepared with 80 µm (No. 8113R, No. 8113NR, Intensiv SA) and finished with 25 µm (No. 3113R, No. 3117, Intensiv SA) diamond burs in a medium- speed handpiece with a water spray and ultrasonic points (SonicSys; Kavo). All the dentin surfaces of the cavity preparations were sealed with an adhesive system (Excite DSC, Ivoclar Vivadent). Undercuts and deep parts of the cavities were covered with a resin composite (Tetric Flow, Ivoclar Vivadent) polymerized for 40 sec. All cavity margins were in enamel and extrasulcus. The distance to marginal

75 gingival was at least 1 mm. Complete mandibular and maxillary arch impressions were taken with a polyvinyl siloxane (Imprint II, 3M ESPE). A light-cured resin (Fermit-N, Ivoclar Vivadent) supported by glass fibers of Pontic (Ivoclar Vivadent) was used as temporary restoration.

Adhesive Procedure The IFPDs restorations were definitively inserted within 2 weeks after the impression was made. The operating field was isolated with a rubber dam, provisional restorations were removed, the teeth were cleaned Tubulicid and rubber cup and pumice slurry and prepared inside restoration surfaces were sandblasted with CoJet system (3M ESPE) with small grain size of 30 µm at 2 bar of pressure for 10 seconds. The inlay bridge was tried to check the fit of the restoration. The inner surfaces of the inlay bridge were sandblasted with CoJet system (3M ESPE) with small grain size of 30 µm at 2 bar of pressure for 10 seconds and a silane-coupling agent (Monobond S, Ivoclar Vivadent). All enamel and dentin surfaces were treated with Excite DSC (Ivoclar Vivadent) according to the manufacturer’s instructions. The dual-cured luting composite Variolink II (Ivoclar Vivadent), was applied to the inlays and the inside of the cavities with a disposable brush. The restoration was inserted in the cavities with a stick and all excess of luting composite was removed. A layer of a glycerin (Liquid Strip; Ivoclar Vivadent) was applied on the margin before the polymerization (Fig. 119). The luting composite was light activated for 60 sec. each from cervical, buccal, lingual and occlusal surfaces. The restorations were then finished with 15 µm diamond burs (Composhape, Intensiv) and polished with a composite finishing and polishing kit (Hawe Neos Dental) and Astrobrush (Ivoclar Vivadent) in a slow-speed handpiece. Occlusion and articulation were carefully checked after the luting step.

Discussion The replacement of missing tooth with a RBFPD is a very conservative prosthodontic treatment especially when the patients refuse the treatment with dental implants. This article describes the replacement of a molar with a conservative inlay bridge resulting in the good success in the short-term follow up.

76 In a previous study on inlay bridge11 the FRC showed good clinical service but these results need more observation in order to create a sound basis for the final assessment of this method. In this study the veneering composite had less fractures with anatomically shaped FRC frameworks which support the occlusal surface of the pontic teeth than with the conventional design. The two important points to achieve the success with this conservative technique are the cavity preparation and the design of the fiber framework. The cavity must give the space to the fiber framework to support completely the pontic element. With only very small preparations such as slots debonding has been a problem. For the retention of Inlay bridges Ivoclar Vivadent recommends at least two surface cavities of the following extension: Depth of occlusal cavity ≥2.5 mm; approximo-central extension ≥4mm; axial depth ≥1.2 mm; proximal step tooth and defect oriented, ideally 2 mm; bucco-oral width ≥3.5 mm. Nevertheless, if the extension of the defect permits, we try to realize a larger axial depth and adopted the following preparation guidelines. Occlusal slot must be 2.0-2.5 mm, occlusal step 2.0 mm, proximal step 2.0 mm, axial depth 2.0 mm and buccal-vestibular width 3.5 or greater. The potential advantages of this technique are self-evident. First, the procedure can be completed in two appointments with low-cost and preservation of sound tooth tissue. Second, the periodontal apparatus of the abutment teeth is not compromised in any way. Third, because this approach is relatively little invasive. It permits the patient to opt for other, more traditional tooth replacement methods in the future. Fourth, repairs can be carried out directly, without the need for any complicated techniques or materials.

References

Creugers NHJ, De Kanter RJ. Patients’ satisfaction in two long-term clinical studies on resin-bonded bridges. J Oral Rehabil 2000;27:602-607. Creugers NHJ, Käyser AF, Van’t Hof MA. A meta-analysis of durability data on conventional fixed bridges: Community Dent and Oral Epidemiol 1994; 22:448- 452.

77 Näpänkangas R, Salonen-Kemppi MAM, Raustia AM. Longevity of fixed metal ceramic bridge prostheses: a clinical follow-up study. J Oral Rehabil 2002;29:140-145. Perdigão J, Lopes M. Dentin bonding-state of art 1999. Compend Contin Educ Dent 1999;20:1151-1162. Freilich MA, Duncan JP, Meiers JC. Preimpregnated, fiber-reinforced prostheses. Part I. Basic rationale and complete-coverage and intracoronal fixed partial denture designs. Quintessence Int 1998:29:689-696. Leal FR, Cobb DS, Denehy GE, Margeas RC. A conservative aesthetic solution for a single anterior edentulous space: case report and one-year follow-up. Pract Proced Aesthet Dent 2001;13:635-641. Hussey DL, Linden GJ. The clinical performance of cantilevered resin-bonded bridgework. J Dent 1996;24:251-256. Freilich MA, Duncan JP, Meiers JC, Goldberg AJ. Preimpregnated, fiber- reinforced prostheses. Part I: basic rationale and complete coverage and intracoronal fixed partial denture designes. Quintessence Int 1998;29:689-696.

Vallittu PK. Flexural properties of acrylic resin polymers reinforced with unidirectional and woven glass fibers. J Prosthet Dent 1999;25:100-105. Vallittu PK. Prosthodontic treatment with a glass fiber-reinforced resin-bonded fixed partial denture: a clinical report. J Prosthet Dent 1999;82:132-135.

78 Chapter 8: Clinical trial 8.2 Randomized controlled trial of Fiber-Reinforced Composite Inlay Fixed Partial Dentures: two-year results.

79 The metal-ceramic fixed partial denture (FPD) is a standard restoration for a single tooth replacement in dental practice. This porcelain-fused-to-metal (PFM) has demonstrated an excellent record of service for many years, but continues to exhibit several drawbacks (Freilich et al 1998). A significant amount of sound tooth structure must be removed when fabricating conventional FPDs. Other potential disadvantages of the conventional FPDs are discoloration of the gingival and visible metal margins or “shine through” effects of the metal frameworks (Kolbeck et al 2002). Moreover base metal alloys may exhibit corrosion and/or may elicit an allergic reaction from a segment of the patient population (Council on Dental Materials, Instruments and Equipment 1995). Implant-supported restorations provide high-quality alternatives to conventional FPDs. However, in some cases the treatment with implants may not be possible: the patient rejects surgical treatment, the costs of implant therapy are too high, not enough bone remaining for the placement of an implant (Sewon et al 2000), poor prognosis of implant therapy due to patient related situations, e.g., smoking (Gruica et al 2004) and insufficient oral hygiene habits (Quirynen et al 2002). In these situations, an inlay fixed partial denture (IFPD) offers a more conservative method of tooth replacement compared to a crown retained conventional bridge because tooth preparations are limited to the occluso and mesio/distal surfaces of abutment (Meiers et al 2001). However these preparations are more technique sensitive and require a careful adhesive luting procedure (Vallittu 2004). Since the bonding procedures strengthen the cusps and provide additional support for dentition, minimally invasive preparation is feasible (Morin et al 1984). The alternatives to conventional PFM prostheses include all-ceramic, all- particulate composite, and fiber-reinforced composite (FRC) systems. The all- ceramic and all-particulate composite systems have been described for FPDs (Kern et al 1991) and IFPDs (Beuchat et al 1999) but, in general, exhibit low resilience and toughness and are subject to fracture (Fischer et al 2003, Zumbuhl et al 2000). FRC is composed of two types of composite materials: fiber composites to build the substructure and a hybrid or microfilled composite to veneer the external surfaces. Initial in vitro investigations of FRC restorations demonstrated promising results. After simulation of oral stresses, the fracture resistance and marginal adaptation of adhesively fixed molar crowns, IFPDs and three-unit complete

80 coverage FPDs were better than for all-ceramic restorations (Loose et al 1998). The fracture resistance of IFPDs showed a mean of about 700N, a value that led to the expectation that these restorations would be successful under clinical conditions (Behr et al 1999). Marginal adaptation of adhesively cemented FRC restorations was shown to remain statistically unchanged after simulation of 5 years of oral stress. It can be concluded from the in vitro wear investigations that the veneering composite will have a wear rate comparable to enamel during a period of 5 years, and that it can bear the load in occlusal contact areas (Kern et al 1999, Knobloch et al 1999). After 2 years of observation, an investigation on forty IFPDs reported 89.6% of continuous margin at the tooth-luting composite interface but four inlay bridges failed for debonding or delamination of veneering material (Göhring et al 2002). Similar results on the survival rate were obtained in two different studies after a three-year observation period using two different FRC systems. Behr (Behr et al 2003) achieved 72% of survival rate using the Targis/Vectris (Ivoclar Vivadent Inc., Schaan, Liechtenstein) system as Freilich (Freilich et al 2002) that reported 75% of survival rate for FiberKor/Sculpture (Pentron Laboratory Technologies LLC, Wallingford, Conn). Fiber-reinforced composite used in IFPDs is a promising material group but little clinical information is available compared to the traditional prosthodontic materials. The purpose of this randomized controlled trial was to collect survival data on posterior IFPDs, using a new microfilled composite in combination with a fiber framework system (SR Adoro/Vectris, Ivoclar Vivadent) placed under controlled clinical conditions and to identify the clinical behaviour of two different bonding systems used to lute the inlay bridges (Excite DSC versus Syntac, Ivoclar Vivadent). The null hypothesis tested in this study was: there is no difference in postoperative sensitivity and clinical behaviour between the two-step dual cured adhesive versus the three-step adhesive bonding system in IFPDs.

MATERIALS AND METHODS Thirty-nine patients were screened and received an indirect restoration. The selection of the patients followed two criteria: their refusal to treatment with dental implants and informed written consent. The study was approved by the Ethics Committee of

81 the University of Bologna. Selection of male and female subjects was restricted to those aged 18-60 years and in good general and periodontal health. Patients with the following factors were excluded from the clinical trial: patients receiving drugs that modify pain perception, pregnancy or breast feeding, eating disorders, periodontal surgery, well-known allergy to chemical compounds used in this study. The inclusion criteria were: patients with a missing tooth, absence of any active perio or pulpal disease, proximal margin located above the cementum-enamel junction, placement of the rubber dam possible and the greatest distance between the abutments was smaller or equal to 12 millimeters. The patients were divided in two groups. In the nineteen patients of group A the Excite DSC adhesive system was used, in those of group B the cementation was carried out with Syntac. The randomization of the patients was performed with the toss of a coin.

From June 2002 to July 2004 thirty-nine IFPDs were inserted. Twenty-two restorations were placed in mandibular teeth and 17 in maxillary teeth and evaluated using the USPHS criteria. Three bridges had been luted to replace the first premolar, fifteen for the second premolar and twenty-one to replace the first molar (Fig. 1-6). Twenty-four restorations were between 2- and 3-year old, eleven bridges were included between one and two years and only four restorations were less 1-year old but had more than six months. Average service time of the IFPDs was 23.4 months.

Clinical Preparation Technique At baseline all patients were tested for dentin sensitivity. In the rank order data, a score of zero was defined as no pain (alpha), 1-4 as mild sensitivity (bravo), which was provoked by the dentists’ air blast, and 5-10 as strong sensitivity (Charlie), which was spontaneously reported by the patient during drinking or eating. The same measurement was performed again at each recall. The status of the gingival tissues adjacent to the test sites was observed at baseline and each recall. Before cavity preparation a rubber dam was placed and all cavities were prepared according to modified principles for adhesive inlays retainers to obtain adequately strong dental restorations. No additional bonding FRC wings were made to obtain more adhesional surface. The cavities were prepared with 80µm (No. 8113R, No. 8113NR, Intensiv SA) and finished with 25µm (No. 3113R, No. 3117, Intensiv SA)

82 diamond burs in a medium-speed handpiece with a water spray. The design of the cavity preparations followed the philosophy of maximal preservation of sound tooth (Göhring et al 1999). Pre-existing restorations were removed and their cavities were used as abutments after appropriate preparation. In situations of primary carious lesions, defect-oriented tooth cavities were prepared within the concept of minimal, but adequately sized, inlay abutments. The cavity had to give the space to the fiber framework to completely support the pontic element. The form of the cavity was at least two surfaces with the following extension: depth of occlusal cavity ≥2.5 mm; occluso-cervical height ≥4mm; axial depth ≥1.2 mm; bucco-oral width ≥3.5 mm. The measurements of the cavities were verified with a periodontal probe after the finishing of the cavity margins. Nevertheless, if the extension of the defect permits, we try to realize a larger axial depth and adopted the following preparation guidelines. A taper of ≈4° (or larger if given by the pre-existing restoration) was chosen to simplify insertion. According to the pre-existing restorations, most proximal boxes were larger. The distribution of the cavity preparations are described in table 1.

All the dentin surfaces of the cavity Table 1 Different distribution preparations were etched for 15” with of the preparations 35% phosphoric acid and sealed with two Slot 9 bonding systems Excite DSC or Syntac Mesio-occlusal 21 (Ivoclar Vivadent). The same adhesive Disto-occlusal 23 system used for the dentin hybridization Mesio-disto-occlusal 14 was employed for the luting procedure. Onlay 5 Undercuts and deep parts of the cavities Overlay 4 were covered in increments with a highly Crown 2 viscous composite (Tetric Ceram, Ivoclar Total abutments 78 Vivadent) polymerized for 40 sec. The excesses of the bonding on the enamel surfaces were removed with 25µm (No. 3113R, No. 3117, Intensiv SA) diamond burs in a medium-speed handpiece with a water spray. All cavity margins were in enamel and extrasulcus. The distance to marginal gingival was at least 1 mm. Complete mandibular and maxillary arch

83 impressions were taken with a polyether material (Permadyne, 3M ESPE). A light- cured resin (Fermit-N, Ivoclar Vivadent) was used as temporary restoration.

Laboratory Technique

According to the manufacturer’s instructions (Transil technique), the Vectris frameworks in the IFPDs were made with pre-impregnated ‘pontic’ and ‘frame’ fibers and all restorations had an anatomical shape of the framework like an oval shape to hold the layering material in a continuous manner and reach a high volume of the substructure. The final design of the bridge’s framework was similar to metal framework with extensions in the vestibular and buccal side to completely support the veneer composite.

The design of the fiberglass framework was first pre-modeled by a photo-curing resin (Spectra Tray, Ivoclar Vivadent) to obtain the oval shape and its thickness checked in the molding model. This model was embedded in a transparent silicone impression paste to form a mould. Then this resin was removed and the fibers were applied into the silicone-mould (Transil, Ivoclar Vivadent). The pre-impregnated ‘pontic’ fibers were condensed into the desired shape by a vacuum- forming process and then cured by light in a VS1 unit (Ivoclar Vivadent) for 10 min. According to the manufacturer’s recommendations, the FRC was treated with silane (Wetting agent, Ivoclar- Vivadent). A sheet of wave fibers ‘frame’ was placed upon the ‘pontic’ structure and the cycle in VS1 was repeated. The SR Adoro material was built incrementally using a Quick light-curing unit. Finally, the IFPD was placed into a Lumamat 100 unit (Ivoclar Vivadent) for the final application of light and heat (104°C) to complete polymerization and maximize strength and other physical characteristics.

Adhesive Procedure The IFPDs restorations were inserted within 2 weeks after the impression was made. The operating field was isolated with a rubber dam, provisional restorations were removed with a sharp probe and the prepared teeth were cleaned with nylon bristle brushes and water spray. The inner surfaces of the inlay retainers were sandblasted with CoJet system (3M ESPE) with small grain size of 30 µm at 2 bar of pressure for 10 seconds. These treated inner surfaces were then silanated by using

84 Monobond-S (Ivoclar Vivadent). Just before the final cementations, the surfaces were the bonding agent (Heliobond or Excite DSC; Ivoclar Vivadent) was brushed on the surfaces and air thinned. To prevent early polymerization of this layer especially for the Heliobond, the bridge was shielded against light until insertion. All enamel finish lines were conditioned with 35% phosphoric acid gel (Ivoclar Vivadent) for 30 seconds whereas the dentin surfaces were etched with the same acid for 15 seconds. The Group A was treated with Excite DSC and Group B with Syntac according to the manufacturer’s instructions. Both the adhesive bonding systems weren’t polymerized before the placement of the luting composite. The bonding agent was blown to a thin layer and the dual-cured composite resin cement Variolink II (Ivoclar Vivadent) was used to lute the restorations. The luting composite was light activated for 60 sec. (Optilux 500, Kerr) each from cervical, buccal, lingual, and occlusal surfaces. Occlusion and articulation were carefully checked after the cementing step. The restorations were then finished with 15 m diamond burs (Composhape, Intensiv) and polished with a composite finishing and polishing kit (Hawe Neos Dental) and silicone-carbide impregnated bristle brushes (Astrobrush, Ivoclar Vivadent) in a slow-speed handpiece. Approximal finishing was performed with flexible discs and abrasive strips (Soflex pop-on; 3M ESPE).

Fig. 1. X-ray preoparatory Fig. 2. Initial status

Fig. 3. The cavity preparation Fig. 4. IFPD made with fiber reinforced composite.

Fig.5. The inlay bridges after the Fig. 6. Follow-up after 2 years. cementation under rubber dam.

Evaluation Two independent examiners (C.M., M.C.) evaluated under magnification (Zeiss 3.6x35mm) all the restorations directly after the final polishing and after one week, 6, 12, 24 and 36 months. At baseline, and at 1-yr and 2-yr examinations, X-rays were performed to check for surplus, marginal gaps, and secondary caries. During the recalls, the patients came back to the office to answer questions about post-operative sensitivity. Partial or total debonding of IFPDs, framework or resin composite fractures and fiber exposures were considered failures. The restorations were evaluated using the USPHS (Ryge et al 1973) modified parameters, to check their stability and longevity in regard to the following characteristics: color match, marginal discoloration, secondary caries, surface texture, marginal adaptation, fracture and postoperative sensitivity. Alpha (α) means perfect condition, Bravo (β) show restorations that are clinically acceptable, Charlie (c) indicate a need for immediate replacement. In cases with only two decision possibilities, eg, debonding or no debonding, the rating comprised only α or c (c= debonding). Plaque growth and gingival health at the gingival pontic surfaces, abutment inlays and contralateral control teeth were also measured using the plaque index (PI) and gingival index (GI). Statistical analysis was applied to compare the restorations at the baseline and after the last recall, and to check for differences between Group A and B. The Wilcoxon’s matched-pairs signed ranks test measured the restorations’ success at the

86 appropriate time intervals and was used to rate all parameters. The Mann-Whitney test was used to compare the data between the two groups. The null hypothesis was rejected at the 5% level. The survival estimation method of Kaplan-Maier was used with statistical software (JMP 5.1).

Table 2. Clinical results based on USPHS criteria after two-year. One week Last One week Last One week Last Abutments α Recall α β Recall c Recall (n=78) β c Groups A B A B A B A B A B A B Marginal 38 40 37 40 ------1 - discoloration Secondary 38 40 38 40 ------caries Marginal 38 40 34 40 - - 4 - - - - - adaptation Postoperative 23 38 36 40 5 2 - - 10 - 2 - sensibility Debonding 38 40 35 40 ------3 -

IFPDs (n=39) Fracture 19 20 17 18 ------2* 2 (including chipping) Surface 18 20 18 20 1 - 1 - - - - - texture Color match 17 17 17 16 2 3 2 4 - - - - Fiber 19 20 19 18 ------2 exposure * The micro fractures were visible only under SEM examination after the detachment of the bridges.

RESULTS The results are summarized in table2. During the observation time, two debondings after 2 and 8 months were detected for the IFPDs luted with Excite DSC bonding system. The detected bridges were immediately replaced with another inlay bridge luted with Syntac. Some micro cracks in the pontic area of the two detached bridges were observed under SEM (Fig. 7a-b). Two fiber exposures were noted after 8 months on the occlusal surface of one IFPD. The framework was visible under low magnification (Zeiss 3.6x35mm) for self-evident color change. This kind of failure was most probably due to the previous occlusal adjustment done after the cementation that had left a thin layer of composite upon the fiber framework. The bridge wasn’t replaced and is under observation now. Some hairline fracture of the veneering materials near the connection between the pontic and the abutment were detected in two cases (Fig. 8-9; a-b). No statistical differences regarding detachment were showed between baseline and last recall between Group A and B (P>0.05). There was no fracture of the pontics, inlay retainers or inlay margins. The IFPDs was always rated “alpha” with respect to secondary caries and surface texture. The two debonded bridges showed “charlie” rating for the marginal adaptation on six abutments and marginal discoloration on one abutment at the last recall. Moderate to severe postoperative sensitivity was rated during the first six months of the observation period. All hypersensitive teeth belonged to group A luted with two-step bonding system. The higher values of sensitivity recorded during the temporary restoration time were reported for group A. These patients primarily reported strong chewing pain during the mastication and less temperature sensitivity (10a-b). The dentinal sensitivity diminished after approximately 12 weeks and completely disappeared after six months in all cases except one abutment that was endodontically treated in the retainer area without removal of the bridge. The statistical analysis showed significant differences (P<0.05) for the sensitivity between group A and group B at baseline and inside of group A during the observation period. Group A showed 42.2% of dentinal sensitivity after 1 month unlike group B that recorded 0%. The percentage of “bravo” for the color match was stable at 86.8% during the observation period and didn’t change at any

88 time. Plaque growth was moderate but no statistical differences occurred in PI and GI between the abutments, pontics and contralateral teeth. The Kaplan-Maier survival estimation was 89.4% for group A and 100% for the group B after 24 months. (Fig 11).

Fig. 7A. Gingival side of the Fig. 7B. The pontic fibers are clearly visible detached bridge. Some fractured under magnification (x1000) after the glass fibers are visible. fracture of veneering composite.

Fig. 8A. The presence of old Fig. 8B. The clinical condition doesn’t restorations on the abutments near the permit to make a fiber framework with edentulous space is the typical situation ideal dimensions. This characteristic for the IFPDs. could cause flexibility of the bridge.

Fig. 9A. The IFPD after 8 months Fig. 9B. The same bridge after 2 years. The finger indicates the hairline fracture of the veneering material in the pontic element near the connection with the inlay.

Fig. 10A. This image represents Fig. 10B. At 1000 magnification are impression of the dentin surface after the clearly visible the ditching created by hybridization with Excite DSC. Some the dentinal fluid. areas show the presence of hallows due to the intrapulpal pressure that could cause the hypersensitivity during the chewing.

1,0 Group B 0,9

0,8

0,7 Group A

0,6

0,5 Surviving 0,4

0,3

0,2

0,1

0,0 0 5 10 15 20 25 Time (months)

Fig. 11. Kaplan-Meier estimation of the cumulative survival rate of IFPDs luted with Excite DSC (group A) and Syntac (group B)

DISCUSSION The results of this study demonstrate that IFPDs made with a light and heat– polymerized microfilled composite bonded with FRC composite exhibited a high percentage of clinical survival in a short observation period particularly in combination with a classic 3-step adhesive bonding system but different discussion points must be argued. The two important points to achieve success with this conservative technique are the design of the fiber framework and the cavity preparation. The design of the FRC framework and the position of the fibers can play an important role in supporting the layering material in a continuous manner and to strengthen the fiber sub-structure. Ellakwa (Ellakwa et al 2004) showed that the different techniques of laboratory construction of fiber framework in the pontic area significantly affected the fracture resistance of fiber-reinforced bridges. Maximizing

90 fiber volume fraction by increasing the proportion of fiber to composite should significantly improve strength (Butterworth et al 2003). The position of the FRC layer can have an effect on the flexural strength. Continuous unidirectional fibers gave the highest strength and stiffness only in the direction of the fiber, while woven fibers were able to reinforce the denture base polymers in two directions (De Boer et al 1984).

The laboratory technique used in this study allows the extension in the vestibular and buccal side to support the layering material like in metal framework and hold it in all loading directions. The framework in the FRC was made in an anatomical shape in the pontic element with parallel and weave fiberglasses. Vestibular and buccal FRC extensions in the pontic element can increase the bonding area between the framework and resin composite as well as hold the veneer material better during occlusal loading. This observation suggested that modified design of frameworks could increase the bond strength of resin composite to the fiber framework when chewing (Monaco et al 2003). A similar approach was used by Freilich (Freilich et al 2002) that hypothesized the increased rigidity and a broader base of support provided by the FRC substructure was needed to support the composite veneer. Thus, they added a substantial amount of FRC bulk to the pontic component of the substructure (low-volume design), resulting in the creation of the “high-volume” substructure design and examined their relationship with the clinical performance. They observed a 95 percent survival rate for the high-volume prostheses in contrast to a 62 percent survival rate for the low-volume prostheses over a 3-year observation period. Similar clinical results were shown in our previous study (Monaco et al 2003) on the relationship between composition and substructure design and clinical performance of Targis/Vectris system after a 4-year follow up period. The authors achieved a 97.5% survival rate for the framework built with parallel and woven fibers modifying the design of the pontic element in an anatomical shape versus a 84% survival rate for the restorations with simplified frameworks made only with parallel fibers. Göhring (Göhring et al 2005) observed 36 posterior FRC IFPDs and after 5 years they reported 71% of survival rate. Most failures were related to delaminations of the veneering material and they are in agreement that modified framework design

91 significantly reduced the delamination rate (Göhring et al 2003). However, long-term clinical studies must be conducted to confirm this hypothesis.

The detachments occurred in two clinical border-line cases. The first happened after 2 months in a patient with parafunctional habits whereas the second occurred after 8 months in a case with long span replacement (11 mm). The examination of the failed bridges under SEM disclosed micro cracks in the gingival areas between the pontic element and the inlay probably due to fatigue phenomena of the veneering material. Lassila (Lassila et al 2004) achieved the highest flexural strength when the FRC layer was located at the tension side of the test specimens. The particulate filler composite is the weaker phase of the system. They demonstrated that when it is located on the tension side, the fracture could easily initiate. The FRC structure benefits most when the tensile stresses can be transferred to the reinforcing fibers. The veneering particulate filler composite is strong in compression stress and, therefore, the FRC structure requires less reinforcement fibers on the compression side. This area represents a tensile zone and the SEM pictures showed the inner glass fiber of the substructures. Key elements for the clinicians include tooth preparation design that must allow an adequate amount of FRC, an accurate interocclusal registration, and proper insertion technique. An inadequate interocclusal registration could results in a considerable occlusal adjustment by the dentist and the potential for inadvertent occlusal exposure of the FRC substructure of an extremely thin layer of the composite veneer in functional areas. Color match of veneering composite (SR Adoro) was extremely stable unlike that of the predecessor material (Targis) that showed in a previous study (Monaco et al 2003) a percentage of bravo in colour match of 29% at the last recall and the deterioration was significant compared to the initial status. In this study, the clinical evaluation of the FRC inlay bridges showed that the microfilled composite veneer material exhibited good colour stability and resistance to wear. The surface texture exhibited no change except for one case with a small chipped area most probably due to a fabrication error.

Group A luted with Excite DSC showed a dentinal sensitivity slightly below 50% after 1 month unlike group B luted with Syntac that didn’t record post-operative

92 sensitivity. Excite DSC is an ethanol-based, two step, dual-curable, single-bottle adhesive. Total etch or simplified adhesives are more sensitive to the technique because optimal hybridization and sealing of dentinal tubules with the wet bonding technique may differ with each bonding system (Frankenberger et al 2000). Ferrari (Ferrari et al 2003) confirmed the sensitivity of the technique with this adhesive system showing in vivo no hybrid layer and extensive nanoleakage after excessive drying and water tree formation along resin-dentin interfaces during excessive wetting. Because the volatile adhesive solvent evaporates quickly, the continuous transudation of dentinal fluid through open dentinal tubules before polymerization of the adhesive may result in the entrapment of water-filled blisters along the adhesive interface (Pashley et al 2002, Tay et al 2003). As the patient masticates, these blisters may create a pumping effect that causes rapid movement of fluid through the tubules, which in turn may trigger the A-delta nerve fibres in the pulpal-dentin complex (Brännström et al 1972). Although most bonded restorations are retained because there is a sufficient well-bonded surface area, a common clinical manifestation of inconsistent bonding within a restoration is the patient’s complaint concerning postoperative sensitivity (Unemori et al 2001). Clinically, no postoperative sensibility was reported by the patients of the group B. This favorable outcome may be related to the three-step adhesive bonding system associated to the methods used in the study to seal the dentin before taking the impression. An accurate control times of the primer and of the bonding agent (>20 s) can ensure against the postoperative sensibility during the temporary period and after the final luting procedure.

Conclusion In a short-term observation period, the FRC showed good clinical service but these results need more observation in order to create a sound basis for the final assessment of this restoration technique. The clinicians and the dental technicians need to strictly follow indications, contraindications and instructions to achieve a satisfactory clinical result. If a conservative inlay FPD is clinically indicated, the patient must be informed that loss of sound hard tissue is minimal but durability of a conventional ceramic fused to metal full coverage FPD and implant treatment is more proven.

93 References

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Ferrari M, Tay FR. Technique sensitivity in bonding to vital, acid-etched dentin. Oper Dent. 2003 Jan-Feb;28:3-8. Fischer H, Weber M, Marx R. Lifetime prediction of all-ceramic bridges by computational methods. J Dent Res. 2003;238-242. Frankenberger R, Kramer N, Petschelt A. Technique sensitivity of dentin bonding: effect of application mistakes on bond strength and marginal adaptation. Oper Dent 2000;25:324-330. Freilich MA, Karmaker AC, Burstone CJ, Goldberg AJ. Development and clinical applications of a light-polymerized fiber-reinforced composite. J Prosthet Dent. 1998;80:311-318. Freilich MA, Meiers JC, Duncan JP, Eckrote KA, Goldberg AJ. Clinical evaluation of fiber-reinforced fixed bridges. J Am Dent Assoc. 2002

94 Nov;133(11):1524-34; quiz 1540-1. Freilich MA, Meiers JC, Duncan JP, Eckrote KA, Goldberg AJ. Clinical evaluation of fiber-reinforced fixed bridges. J Am Dent Assoc. 2002;133:1524-1534 Göhring TN, Mörmann WH, Lutz F. Clinical and scanning electron microscopic evaluation of fiber-reinforced inlay fixed partial dentures: preliminary results after one year. J Prosthet Dent 1999; 82: 369-377. Göhring TN, Roos M. Inlay-fixed partial dentures adhesively retained and reinforced by glass fibers: clinical and scanning electron microscopy analysis after five years. Eur J Oral Sci, 2005; 113: 60–69. Göhring TN, Schmidlin PR, Lutz F. Two-year clinical and SEM evaluation of glass- fiber-reinforced inlay fixed partial dentures. Am J Dent. 2002;15:35-40. Göhring TN, Zappini G, Mayer J, Zehnder M. Optimization of glass-fiber framework for fixed partial dentures: Laser-interferometrical analysis. Quintessenz Int 2003; 35: 668–675. Gruica B, Wang HY, Lang NP, Buser D. Impact of IL-1 genotype and smoking status on the prognosis of osseointegrated implants. Clin Oral Implants Res. 2004;15:393-400. Kern M, Knode H, Strubb JR. The all-porcelain, resin-bonded bridge. Quintessence Int. 1991;22:257-262. Kern M, Strub JR, Lu XY. Wear of composite resin veneering materials in a dual-axis chewing simulator. J Oral Rehabil. 1999;26:372-378. Knobloch LA, Kerby RE, Seghi R, van Putten M. Two-body wear resistance and degree of conversion of laboratory-processed composite materials. Int J Prosthodont. 1999;12:432-438. Kolbeck C, Rosentritt M, Behr M, Lang R, Handel G. In vitro examination of the fracture strength of 3 different fiber-reinforced composite and 1 all-ceramic posterior inlay fixed partial denture systems. J Prosthodont. 2002;11:248-253. Lassila LVJ, Vallittu PK. The effect of fiber position and polymerization condition on the flexural properties of fiber-reinforced composite. J Contemp Dent Pract 2004;2:014-026. Loose M, Rosentritt M, Leibrock A, Behr M, Handel G. In vitro study of fracture strength and marginal adaptation of fiber-reinforced-composite versus all

95 ceramic fixed partial dentures. Eur J Prosthodont Restor Dent. 1998;6:55-62. Meiers JC, Freilich MA. Chairside prefabricated fiber-reinforced resin composite fixed partial dentures. Quintessence Int. 2001;32:99-104. Monaco C, Ferrari F, DDS, Miceli GP, Scotti R. Clinical Evaluation of Fiber- Reinforced Composite Inlay Fixed Partial Dentures. Int J Prosthodont 2003;16:319- 325. Monaco C, Miceli GP, Scotti R. Die mit dem neuen, mikrogefüllten Komposit- Material SR Adoro verblendete Inlay-Brücke. Quintessenz Zahntech 2003;3:292- 305. Morin D, DeLong R, Douglas WH. Cusp reinforcement by the acid-etch technique. J Dent Res. 1984;63:1075-1078 Pahley DH, Pashley EL, Carvalho RM, Tay FR. The effects of dentin permeability on restorative dentistry. Dent Clin North Am 2002;46.211-245. Quirynen M, De Soete M, van Steenberghe D.Infectious risks for oral implants: a review of the literature. Clin Oral Implants Res. 2002;13:1-19. Report on base metal alloy for crown and bridge applications: benefits and risks. Council on Dental Materials, Instruments and Equipment. J Am Dent Assoc 1995;111:479-483. Ryge G, Snyder M. Evaluating the clinical quality of restorations. J Am Dent Assoc 1973;87:369-377. Sewon LA, Ampula L, Vallittu PK. Rehabilitation of a periodontal patient with rapidly progressing marginal alveolar bone loss: 1-year follow-up. J Clin Periodontol. 2000;27:615-619. Tay FR, Pashley DH. Have dentin adhesives become too hydrophilic? J Can Dent Assoc 2003;69:726-731. Unemori M, Matsuya Y, Akashi A, Goto Y, Akamine A. Composite resin restoration and postoperative sensitivity: clinical follow-up in an undergraduate program. J Dent 2001;29:7-13. Vallittu PK. Survival rates of resin-bonded, glass fiber-reinforced composite fixed partial dentures with a mean follow-up of 42 months: a pilot study.J Prosthet Dent. 2004;91:241-246. Zumbuhl R, Lutz F, Krejci I. In-vitro studies of resin-bonded slot composite bridges

96 compared to conventionally prepared composite bridges. Schweiz Monatsschr Zahnmed. 2000;110:505-522.

97 Chapter 9: Alternative materials as regards FRC Fatigue test in shear: its effect on bond of a glass-infiltrated alumina ceramic to human dentin, using different luting procedures.

98 The concepts of minimally invasive dentistry combined with adhesive technique have been highly recommended because it’s based on the conservation of dental structure. (Degrange et al 1997). Hence, the ceramic partial restorations compared with complete crowns present this conservative approach because they are minimally invasive. Thus, it is important that the enamel/dentin and the ceramic substrate are appropriately conditioned to optimize this adhesive process. (Özcan 2002, Özcan & et al 2002, Özcan 2003, Özok et al 2004,Reis et al 2004). With the increase of aluminum oxide content (Al2O3) in feldspar ceramics, there is a significant improvement in the mechanical properties allowing metal-free restorations to be employed more predictably (Tinschert et al 2000, Guazzato et al 2004). In posterior teeth with high mechanical loading, the ceramics with high crystalline content (aluminum and/or zirconium oxides) have presented better clinical results than feldspar-, leucite-, and lithium disilicate-based ceramics (Scotti et al 1995, Oden et al 1998, Hayashi et al 2000, Fradeani et al 2002). However the increase of the mechanical strength, by increasing the crystalline content and decreasing the glass content, results in an acid-resistant ceramic whereby any type of acid conditioning produces insufficient surface changes for adequate bonding to resin. (Awliya et al., 2000, Derand et al 2000, Madani et al 2000, Ozcan et al 2001, Della Bona et al 2002, Özcan et al 2003). Thus, even though the etching with hydrofluoric acid combined with the silanization is the principal conditioning method of feldspar-, leucite- and lithium disilicate-based ceramics (silica-based ceramic) (Della Bona et al 2000, Debnath et al 2003, Borges et al 2003, Özcan et al 2003, Della Bona 2004, Melo et al 2005). This conditioning method does not allow high bond strength to acid-resistant ceramics (Awliya et al 2000, Derand et al 2000, Madani et al 2000, Ozcan et al 2001, Della Bona et al 2002). Currently, the tribochemical silica coating method appears to be the choice conditioning for the acid-resistant ceramic. (Kern et al 1995, Awliya et al 1998, Özcan et al, 2001, Özcan et al 2003, Bottino et al 2005, Valandro et al 2005, Valandro et al 2005, Amaral et al 2005). Due to the high-speed surface impact of the alumina particles modified by silica, there is an embedding of these particles on the ceramic surface (Sun et al 2000). Consequently, there is a chemical bond between the silica coated ceramic surface and the silane agent (y- methacryloxypropyltrimethoxysilane), and the latter to the resin material.

99 Furthermore these tribological concepts, the resin cements with MDP monomers (10-methacryloyloxydecyl-dihydrogen-phosphate) have allowed high bond strength to acid-resistant ceramics, as well as high bonding durability, due to the bond between the phosphate monomers and the aluminum/zirconium oxides of the dental ceramic (Kern et al 1998, Wegner et al 2000, Özcan et al 2001, Friederich et al 2002, Wegner et al 2002, Blatz et al 2003 Özcan et al 2003, Blatz et al 2004, Hummel et al 2004, Leite et al 2005). Bond strength- (Ozturk et al 2003) and microleakage-tests (Jacques et al 2003) can be used to evaluate the bonding between the dental substrate and the ceramic. However, mechanical fatigue tests conducted in a humid environment seem to be the best in vitro method to predict the clinical performance of dental materials and restorative techniques. Fatigue is a type of test that may lead to the fracture of a structure after repeated loading, and may be explained by the spread of microscopic cracks from areas of force concentration, usually in areas containing macroscopic or molecular structural defects (Pontius et al 2002, Scotti et al 2002, Wiskott et al 1995). Pontius (Pontius et al 2002) described that 1,200,000 cycles in a mechanical fatigue test correspond to approximately 5 years of clinical function. Thus, the purpose of this study was to evaluate the fatigue resistance of the bonding between human dentin and glass-infiltrated aluminum-based ceramic, using different luting materials. The hypothesis was that the fatigue resistance can be modified depending on used luting procedures.

MATERIAL AND METHODS

Selection and preparation of teeth

Forty extracted, caries-free human third molars were used. The teeth were collected in the Dept. of Oral Science (University of Bologna), after obtaining the patient’s informed consent. After the extraction, the teeth were immediately immersed in 0.02%-thimol/24h and stored in distilled water. Part of the crown was removed, exposing a flat dentin surface of approximately 3mm x 4mm, which was polished on wet #320, 600, 1000-grit silicon carbide (SiC) paper, respectively, for 60s to standardize the smear layer.

100 After preparation, each specimen was embedded in a PVC cylinder (height: 20mm, diameter: 10mm) filled with chemically cured epoxy resin (Epoxy Resin 285, Schaller, Florence, Italy), remaining exposed only the dentin surface for luting.

Preparation of alumina ceramic samples

Forty ceramic blocks of a glass-infiltrated alumina ceramic (In-Ceram Alumina for Cerec 2) (VITA Zahnfabrik, Bad Säckingen, Germany) were fabricated according to the manufacturer's specifications. These blocks were 3mm x 3mm x 4mm in dimension and the bonding surfaces (3mm x 3mm) of each block were polished using a 600- to 1200-grit metallographic (3M, St. Paul, USA) in a polishing machine. The surfaces of all the ceramic blocks were submitted to the

chairside airborne abrasion with 110µm aluminum oxide particles (Al2O3), following this blasting protocol: a = perpendicular to the surface; b = 10-mm distance; c = 20-second time; d = 2.8-bar pressure.

Luting procedures

The materials used in this study and the luting technical procedures are described in Table 1. Four luting protocols were tested following the manufacturer’s recommendations (luting system [LS] / ceramic surface conditioning [CSC]). The tooth- and ceramic- sp were randomly divided in four groups (n=10):

GROUP 1: [LS] RelyX Unicem / [CSC] Al2O3;

GROUP 2: [LS] One-Step + Duo-Link / [CSC] Al2O3 + etching with 4% hydrofluoric acid (Porcelain Etchant) + silane coupling agent (Porcelain Primer).

GROUP 3: [LS] Panavia F / [CSC] Al2O3.

GROUP 4: [LS] Scotchbond 1 + RelyX ARC (3M-Espe) / [CSC] Al2O3 + chairside

airborne abrasion with siliceous acid modified by 30µm Al2O3 particles (Si2Ox)

(blasting procedures: identical to the airborne abrasion with Al2O3) + silane coupling agent (Tribochemical silica coating) (CoJet System);

101

After the ceramic conditioning and application of the adhesive systems (excepted in G1), the luting cements were manipulated as recommended by the manufacturers and applied on the bonding surface of each ceramic block, which was than cemented to dentin surface. The set-up remained under the constant load of 750g for 10min and during this period the cement excesses were removed. The specimens (sp) were stored in distilled water to 37oC for 24 h and then were submitted to the fatigue test.

Mechanical fatigue test in shear (Figure 2 and 3)

Initially, all sp were grasped in an apparatus, which allows the dentin surface to be almost perpendicular to the fatigue test. A metallic cylinder were then positioned on the ceramic surface (perpendicular to dentin surface) and the sp were subjected to 1 million fatigues cycling shear with sinusoidal load ranging from 0 to 21N at 8Hz frequency and 37°C water irrigation.

Fatigue resistance scores and statistical analysis

After the fatigue test, it was given a classification (score) for fractured and no- fractured sp based on the number of the mechanical cycle:

Score 0: samples fractured before cycling. Score 1: samples fractured between 0 and 199,999 cycles. Score 2: samples fractured between 200,000 and 399,999 cycles. Score 3: samples fractured between 400,000 and 599,999 cycles. Score 4: samples fractured between 600,000 and 799,999 cycles. Score 5: samples fractured between 800,000 and 999,999 cycles. Score 6: samples non-fractured up to 1 million cycles.

The collected data were submitted to statistical analysis (Kruskal- Wallis test and post hoc Tukey test), using a level of significance of 5%.

102

Analysis of the failure modes

The fractured sp during the fatigue test were analyzed in a Scanning Electron Microscopy (magnification from x200 to x1000) (JEOL–JSM–5400, Jeol Ltd, Tokyo, Japan) in order to evaluate the sp failure mode, which were classified in seven types: Type 1) fracture of the luting cement (cohesive); Type 2) fracture of the dentin (cohesive); Type 3) cohesive fracture of the ceramic (cohesive); Type 4) failure between dentin and adhesive system (adhesive failure); Type 5) failure between luting cement and ceramic (adhesive failure); Type 6) mixed failure (type 1 + type 4); Type 7) mixed failure (type 1 + type 5); Type 8) mixed failure (type 4 + adhesive failure between resin cement and bonding agent). All micrographics were analyzed by three calibrated observers.

RESULTS

The Kruskal-Wallis nonparametric analysis of the fatigue resistance scores are shown in Table 2, in which it was possible to note that there were differences among the studied groups.

The mean score values and standard deviations of the groups are shown in Table 3, noting that G3 (Score = 5.9 [1 failure]) and G4 (Score = 6 [none failure]) were statistically similar (P=0.33) and had significantly the highest fatigue resistance, when compared to G1 (Score = 3.9 [5 failures]) and G2 (Score = 3.7 [6 failures]) (P<.03).

In the fractured sp microscopic analyses it was observed that: (1) G1 – 5 fractures type 4 (Figure 4); (2) G2 – 6 fractures type 5 (Figure 5); G3 – 1 fracture type 8 (Figure 6).

DISCUSSION

The hypothesis of this study was confirmed, since the fatigue resistance was different depending on the protocol used to lute the glass infiltrated alumina

103 ceramic to the dentin. The highest fatigue resistances were obtained whether by the combination of self-etching primer with MDP-based resin cement (G3) or the combination of total etching/single bottle with resin cement/tribochemical silica coating (G4).

The results for G3 may be explained by the combination of the chemical bonds between the MDP phosphate monomers and the aluminum oxides (Wegner et al 2000, Özcan et al 2001, Blatz et al., 2003, Hummel et al 2004, Leite et al 2005), and the dentin treated with self-etching primer. (Uno et al 2000, Varela et al 2003) For G4, the results may be explicated by the chemical bond among silica coated ceramic surface, silane agent and the resin material, (Kern et al 1995), combined with the adequate bonding of the adhesive system to the dentin (Abu-Hanna et al 2004, Helvatjoglu-Antoniades et al 2004, Reis et al 2004).

The performance of resin cements that contain MDP phosphate monomers (10-methacryloyloxydecyl-dihydrogen-phosphate) (G3) have been observed by various studies, which noted a high bonding durability of this cement to acid-resistant ceramics, such as glass-infiltrated alumina/zirconium ceramic (Kern et al 1995, Ozcan et al 2001), yttrium-oxide-partially-stabilized zirconia ceramic (Kern et al 1998, Wegner et al 2000, Wegner et al 2002, Blatz et al 2004), densely-sintered alumina ceramic (Friederich et al 2002, Blatz et al. 2003, Hummel et al 2004).

Despite the resin cement of G3 was bonded to the acid-resistant ceramic, one sp showed a failure type 8, since the fracture occurred in two zones: partial fracture between dentin and adhesive system, and partial fracture between the adhesive system and resin cement (Panavia). Even though this fracture has not been statistically significant, since G3 (1 fracture) was statistically similar to G4 (none fracture), it maybe explained due to the features of the dentin adhesive system and the resin cement employed in G3. The employed self-etching primer adhesive system exhibited a low pH value, producing a chemical match with the polymerization chemical process of the dual-cure resin cement. Some studies have indicated a possible chemical incompatibility between adhesive systems

104 with low pH and resinous materials of chemical- and dual-polymerization. (Sanares et al 2001, Cheong et al 2003, Suh et al 2003, Tay et al 2003, Tay et al 2003). A correlation was observed between the decline in microtensile bond strengths of chemical-cured composites coupled to bonded dentin and the acidity of these adhesives. (Sanares et al 2001) Since single-step self etch adhesives contain a higher concentration of acidic resin monomers, the coupling of chemical/dual-cured composites to the hydrated dentin bonded with these adhesives were also found to be inferior to those achieved by using light-cured composites. It is known that acidic resin monomers retard the polymerization of chemical/dual-cured composites that are initiated via peroxide-amine type binary redox catalysts. Interaction between acidic adhesive resin monomers and the basic composite tertiary amines results in the consumption of the latter in acid- base reactions, depriving their capacity of generating free radicals in subsequent redox reactions. (Suh et al 2003, Tay et al 2003).

In this current study, it was observed that none of the G4 specimens fractured during the fatigue test, meaning that the two interfaces (resin cement– ceramic; dentin-adhesive system) supported the fatigue. The high bond-strength and -durability promoted by tribochemical silica coating combined with resin cement has also been stated by studies. (Kern et al 1995, Awliya et al 1998, Özcan et al 2001, Özcan et al 2003, Bottino et al 2005, Valandro et al 2005, Valandro et al 2005). The fatigue resistance of the interface cement-ceramic can be explained by the following phenomena: the airborne particle abrasion allows the ceramic surface to be embedded by silica oxide coated aluminum particle (Sun et al 2000) forming the silica-modified surface chemically more reactive to the resin via silane coupling agents. Silane molecules react with water to form three silanol groups (–Si–OH) from the corresponding methoxy groups (–Si–O–

CH3). (Plueddemann 1970, Ozcan et al 2003, Ozcan et al 2004) The silanol groups then react further to form a siloxane (–Si–O–Si–O–) network with the silica surface. Monomeric ends of the silane molecules react with the methacrylate groups of the adhesive resins in a free radical polymerization process. (Plueddemann 1970, Jedynakiewicz et al 2001, Ozcan et al 2003, Ozcan et al 2004). Summarizing, the employed tribochemically assisted system

105 (chairside system) allows a chemical bond among the coated silica, silane coupling agent and resin cement. Regarding the fatigue resistance of the interface dentin-adhesive system, some studies stated that the adhesive system used in this group (G4) present high dentin bond strength (Abu-Hanna et al 2004, Helvatjoglu-Antoniades et al 2004, Reis et al 2004), due to the hybridization of dentin (Koshiro et al 2004), as well as the compatibility between the bonding agent and the resin cement (Sanares et al 2001), which justified the resistance to the fatigue.

Analyzing the micrographics of the 5 fractured sp of G1 (Figure 4), it was noted that the failure occurred in the interface dentin – resin cement (type 4). In this micrographic, the dentin surface coated by the smear layer can also be observed. This smear layer was not removed because the dentin is not etched and any bonding agent was applied as recommended by the manufacturer. Thus the hybrid layer is not formed and the bonding between the cement and the dentin did not support the mechanical fatigue, explaining the type of fracture.

In G2, 6 fractures type 5 were observed (failures between the resin cement and ceramic surface). The ceramic surface conditioning (4% hydrofluoric acid + silane coupling agent) recommended for this luting protocol justified the noted fracture pattern. Currently, it is stated that the hydrofluoric acid does not present ability to attack the compact ceramic surface with high alumina content and low vitreous phase (acid-resistant ceramic), such as the ceramic employed in the current study (glass-infiltrated alumina ceramic) (Awliya et al 1998, Derand et al 2000, Madani et al 2000, Ozcan et al 2001, Della Bona et al 2002 Borges et al 2003, Özcan et al 2003). This glass infiltrated high-alumina core ceramic is composed of approximately 80w% of crystalline phase (aluminum oxide) and 20w% of glassy phase (aluminum-silicate-lanthanum) (Tinschert et al 2000, Guazzato et al 2004). Hence, due to the low silica content in this ceramic, the application of the silane agent also does not contribute to bonding, because the MPS-based silane agent presents a great chemical bond to silica oxides and a weak bond to aluminum oxides, which is the basis ingredient of alumina ceramic (Plueddemann 1970, Kern et al 1994, Ozcan et al 2003, Ozcan et al 2004). Exactly as stated by Valandro (Valandro et al 2005) the ceramics can be

106 classified into groups depending on how the surface is attacked by the hydrofluoric acid (HF). Acid-sensitive ceramics are promptly etched by HF resulting in micro-mechanical retentive ceramic surfaces (e.g.: feldspar-, leucite- and lithium disilicate-based ceramics) (Della Bona et al 2000, Debnath et al 2003, Borges et al 2003, Özcan et al 2003, Della Bona et al 2004, Melo et al 2005). Acid-resistant ceramics do not suffer much surface degradation by HF etching, preventing a reliable micro-mechanical bond to resin (e.g.: glass-infiltrated alumina and zirconia ceramic systems, densely-sintered alumina ceramics, and yttrium-oxide-partially-stabilized zirconia ceramics) (Ozcan et al 2003, Bottino et al 2005, Valandro et al 2005, Amaral et al 2005).

However, considering the micrographics of the fractured sp of G2, it can be noted that the interface dentin – adhesive system resisted to the fatigue test. Thus, the bonding of the G2 adhesive system to the dentin maybe considered safe, in light of the parameters followed in this study. Some studies have shown that One Step adhesive system presents high bond strength to the dentin (Cheong et al 2003, Abdalla et al 2004).

Taking into account the results obtained in G2, in which the bonding to the dentin was stable and the bonding to the ceramic did not resist to mechanical fatigue, the clinicians should reflect on the choice of the adhesive system to bond the dentin and the ceramic surface. For example, if the manufacturer’s instructions regarding the ceramic surface conditioning were not followed, namely if the surface ceramic had been conditioned with a tribochemical silica coating method, in view of the current concepts of adhesion to acid-resistant ceramic, theoretically the fractured observed fracture in the interface resin cement – ceramic could not have occurred. The clinicians should attentively observe some aspects during the luting of all-ceramic restorations. Even though the manufacturer’s instructions should obviously be considered, a global view regarding the current concepts to treat the dental hard tissues, as well as the conditioning of the ceramic surface must be considered in order to optimize the global performance of the bonded ceramic restorations.

107 Surely, other factors such as the case preview must be planned, the characteristics of the prosthetic preparations and generally the conditions for the cementation can affect the global performance, and therefore further clinical evaluation studies are necessary to state the effect of the change of luting protocols or the mixing of different protocols. The combination of dentin adhesive systems with MDP-based resin cement or resin cement/tribochemical silica coating were the best luting protocols for aluminous ceramic. The cementation strategies of glass-infiltrated alumina ceramic recommended by the manufacturers maybe eventually changed in order to optimize the bond to all the substrate.

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111 Scotti R, Catapano S, D’Elia A. A clinical evaluation of In-Ceram crowns. Int J Prosthodont 1995;8:320-323. Scotti R, Ferrari M. Proprietà mechaniche e valutazione in vitro. In: Perni in fibra: Presupposti teorici ed applicazioni cliniche. Milan: Masson 2002;39-51. Suh BI, Feng L, Pashley DH, Tay FR. Factors contributing to the incompatibility between simplified-step adhesives and chemically-cured or dual-cured composites. Part III. Effect of acidic resin monomers. J Adhes Dent 2003;5:267-282. Sun R, Suansuwan N, Kilpatrick N, Swain M. Characterization of tribochemically assisted bonding of composite resin to porcelain and metal. J Dent 2000;28: 441-445. Tay FR, Pashley DH, Yiu CK, Sanares AM, Wei SH. Factors contributing to the incompatibility between simplified-step adhesives and chemically-cured or dual- cured composites. Part I. Single-step self-etching adhesive. J Adhes Dent 2003;5:27- 40. Tay FR, Pashley DH. Resin bonding to cervical sclerotic dentin: a review. J Dent 2004;32:173-196. Tay FR, Suh BI, Pashley DH, Prati C, Chuang SF, Li F. Factors contributing to the incompatibility between simplified-step adhesives and self-cured or dual-cured composites. Part II. Single-bottle, total-etch adhesive. J Adhes Dent 2003;5:91-105. Tinschert J, Zwez D, Marx R, Anusavice KJ. Structural reliability of alumina-, feldspar-, leucite-, mica- and zirconia-based ceramics J Dent 2000;28:529-535. Uno S, Tanaka T, Kawamoto C, Konishi J, Sano H Microtensile bond strength to dentin and cavity adaptation of Cerec 2 inlay restoration Am J Dent 2000;13:59. Valandro LF, Della Bona A, Bottino MA, Neisser MP. Bonding to densely sintered alumina ceramic: The effect of ceramic surface treatment. J Prosthet Dent 2005;93:…-….. Valandro LF, Leite FPP, Scotti R, Bottino MA, Neisser MP. Effect of ceramic surface treatment on the microtensile bond strength between a resin cement and an alumina-based ceramic. J Adhes Dent 2004; 6(4):327-332. Varela SG, Rábade LB, Lombardero PR, Sixto JML, Bahillo JDG, Park SA. In vitro of endodontic post cementation protocols that use resin cements. J Prosthet Dent 2003;89:146-153.

112 Wegner SM, Gerdes W, Kern M. Effect of different artificial aging conditions on ceramic-composite bond strength. Int J Prosthodont 2002;15:267-272. Wegner SM, Kern M. Long-term resin bond strength to zirconia ceramic. J Adhesive Dent 2000;2:139-147. Wiskott HWA, Nicholls JL, Belser UC. Stress fatigue: Basic principles and prosthodontic implications. Int J Prosthodont 1995;8:105-116.

113 Chapter 10 Other clinical application of FRC Clinical evaluation of teeth restored with quartz fiber-reinforced epoxy resin posts.

114 Both researchers and manufacturers have introduced several post-and-core restorations with the aim of providing reliable systems for reconstruction of endodontically treated teeth. In spite of these efforts, it is still difficult to predict the clinical survival times of treated teeth restored with posts and cores (Goodacre et al 1994). The prognosis is related to several factors, including the type of material used for the post and core; the shape, dimensions, and length of the post; and the kind of cement used. The major disadvantage associated with conventional cast-metal posts is vertical root fracture. Having high rigidity, metal posts appear to vibrate at high frequencies when loaded with lateral forces. The focusing of these forces in unpredictable “critical points” may determine longitudinal fractures of the root or metal corrosion and consequently lead to loss of the tooth (Trabert et al 1984, Morgano et al 1993, Duret et al 1990). In 1990, Duret (Duret et al 1990) proposed carbon-fiber posts, among the many prefabricated fiber post-and-core systems, to reduce the failure rate. These relatively recent posts are made of equally aligned carbon fibers attached to an epoxy resin matrix and present an interesting property, anisotropic behaviour. In other words, the material has different physical responses when loaded in different directions. This characteristic is of clinical relevance, as it may strongly reduce the possibility of root fracture and decementation (Morgano et al 1993). The objective is to create a “cement-post-core” system with homogeneous properties and physical characteristics similar to tooth tissues. To fulfill esthetic requirements, quartz- and glass-fiber posts embedded in a filled resin matrix have been developed. According to the manufacturer, the mechanical properties of these posts are similar to those of carbon posts and provide an additional esthetic benefit. Fiber posts appear to be biocompatible, are easy to insert, and are time and cost effective. Moreover, there is no need for temporary fillings, since the post is placed using a one-stage technique. The system is conservative with regard to the remaining dental structure and offers the possibility of orthograde retreatment in cases of endodontic failure (de Rijk 2000). Several in vitro studies have been conducted on carbon- fiber posts, although only a few investigations have been carried out on the esthetic quartz-fiber post system. Relatively few reports have evaluated the in vivo effectiveness of carbon- and quartz-fiber posts.

115 A 6-year clinical study using carbon-fiber posts (Composiposts) (Dallari et al 1996) reported two failures in 575 restorations. A retrospective study (Fredrikson et al 1998) reported that the Composipost system performs favorably after 2 to 3 years. In fact, only 2% of treated teeth had to be extracted, and none of these failures were attributable to the fiber post system. Others (Ferrari et al 2000) evidenced a 3.2% failure rate among 1,304 treated teeth restored with carbon- and quartzfiber posts in a 6-year study. Neither of these studies reported root fractures. The purpose of the present prospective clinical follow-up was to evaluate the survival rate of 180 endodontically treated teeth restored using quartz-fiber posts and composite resin material, and finalized with metal-ceramic or all-ceramic crowns over a 30- month period.

Materials and Methods

One hundred eighty endodontically treated teeth in 132 patients (aged 18 to 65 years) were restored by 13 different operators (Table 1). Restored teeth had the following characteristics: need for prosthetic crown, root canal therapy performed at least 3 months previously with no subjective or objective symptoms, and no lesions visible upon radiography. Radiographs were taken with the long-cone technique when the restoration was performed and were examined with approximately 5_ magnification. Teeth were restored with Æstheti-Plus quartz-fiber posts (RDT) (Figs 1 and 2). This post system is composed of equally aligned quartz fibers that are longitudinally embedded in an epoxy resin matrix. Posts are available in three sizes, have a cylindric, double-section shape, and are 22 mm long. Post 1 has a diameter of 1.4 mm in the wider cylindric section and 1.0 mm at the narrow end, post 2 has a diameter of 1.8 mm at the large end and 1.2 mm at the narrow portion, and post 3 has diameters of 2.1 mm and 1.4 mm, respectively. This special shape is apparently better adapted to the prepared canal. The choice of three different diameters provided the possibility to find the adequate post dimension following the criteria of maximum conservation of the residual dental tissue. In accordance with previous studies (Fredrikson et al 1998 Chalifoux 1998) the following parameters were considered relevant: number of canals; remaining tooth tissue, defined as complete (C; 66% to 100% of the tooth), partial (P; 33% to 65% of the tooth), or absent (A; 0% to 32% of

116 the tooth), shape of the canal space; and tooth antagonist. Among the 180 treated teeth, 69% percent presented one root canal, and 31% percent had two or three canals. In 14 maxillary premolars and 11 molars (four maxillary and seven mandibular ones), the restorations were done with the anchorage of two posts per tooth. Thus, among the 180 teeth restored, 205 canals were treated, and the same number of posts was used. Seventy-nine percent of the canals treated showed a round shape (R), 19% an oval one (O), and 2% a semicircular shape defined as C. Of the opposing occluding teeth, 53% were natural teeth, 19% had metal-ceramic crowns, 16% were dentures, 11% occluded with metal-resin crowns, and 1% were not in occlusion.

Clinical Procedures

Prior to cavity preparation, a rubber dam was placed, and provisional restorations were removed with 80- µm diamond burs (205, Intensiv) in a medium-speed handpiece under water cooling. Following direct clinical observation and radiographic examination, the operator selected the most suitably sized fiber post. Root preparation was done with a Pre-forma Drill and a Forma Drill in a slow-speed handpiece with water spray. These calibrated burs provided a uniform preparation and a thin and equally distributed layer of resin surrounding the post after its cementation. The post was then reduced to the proper length using an 80-µm diamond bur (206, Intensiv) in a highspeed handpiece with water spray; the bur was kept perpendicular to the long axis of the post to avoid damaging the fiber structure and its mechanical characteristics. The length of the post was at least equal to the length of the clinical crown, always respecting the apical gutta percha seal of 4 mm. The root canal was treated with 32% phosphoric acid (Bisco) for 15 seconds, rinsed with deionized water, and gently dried with air and a paper cone to verify that no traces of acid remained in the root preparation. Equally mixed primers A and B (Bisco) were applied with a Superfine Microbrush (Microbrush) in the canal and on the post surface and then gently dried to permit the evaporation of the acetone. Pre-Bond (Bisco) was applied inside the canal with a paper cone. Next, the two components of the self-curing C&B Resin Cement (Bisco)

117 were mixed and applied at the edge of the root and on the post, which was immediately placed into the prepared canal. The excess cement was trimmed and given an adequate setting time (Fig 3). Core buildup was then performed using Core- Flo (Bisco) or Bis-Core (Bisco) self-curing resin composite. Clinical recalls were performed at 6, 12, 24, and 30 months. At the last recall, all teeth were crowned. Three dentists evaluated the clinical performance of the restored teeth. The observers were not blinded. Outcome was considered successful if the post and core were in situ with no displacement or detachment of the post, no crown or prosthesis decementation, and no post, core, or root fracture. Subjective symptoms reported by the patients were considered potential signs of failure.

Results After a period of 30 months, three failures were recorded; all took place during the temporary phases during removal of the resin temporary restoration. The first failure, recorded after 2 weeks in a maxillary left first premolar, was a cohesive fracture at the edge of the composite resin of the core and did not involve the post structure. The remaining dental structure was classified as P (33% to 65%), the canal shape was oval, the post used had a diameter of 1.4 mm (post 1), the length of the post was 8 mm (slightly longer than the clinical crown), and the antagonist was a natural tooth. After the fracture, the restoration was immediately replaced and the case was finalized, and the post was still working successfully after 30 months. The second and the third failures were adhesive fractures involving the cement-post-core detaching from the dentinal walls of the root canal. The failures involved two canines (one maxillary and one mandibular). Both teeth presented a rather low remaining tooth structure (A; 0% to 32%) and a very large canal diameter, probably because of excessive preparation during the endodontic therapy. Number 2 posts, which have a diameter of 1.8 mm in the upper portion, had been used; in spite of this, a thick layer of cement was around the posts. The lengths of the posts were 11 mm and 9 mm, respectively. The 9-mm post was somewhat shorter than the clinical crown. Its length had been imposed by the short root and the necessity to leave an adequate seal of the apex. The antagonist was a natural tooth in one case and a ceramic crown in the other. In both cases, the post and core were replaced immediately. The cases were finalized and were still successful as of this writing. No crown or prosthesis

118 decementations or post, core, or root fractures were recorded. No significant variations in terms of health of periodontal tissues were observed. No caries were detected, and no subjective symptoms were reported. The three failures represented 1.7% of all treated teeth, giving a cumulative survival rate of 98.3% in a Kaplan- Meier survival curve.

Discussion

The implementation of a new, homogeneous post and- core system is a good starting point for the creation of a reliable substructure for prosthetic rehabilitation. In combination with resin adhesive systems, resin cements, and composite resins, fiber posts present biomechanical characteristics similar to those of the dentin. To date, the favourable clinical outcomes observed encourage more widespread use. In combination with the resin cement and composite resin restoration, the clinical performance of the Æstheti-Plus fiber posts was good over a 30-month period. The causes underlying the three precocious failures of the three restorations were examined in detail. In the first case, a cohesive fracture, a bubble embedded in the composite resin was found. The defect may have been due to insufficient polymerization, possibly because of operator error. In the second and third cases, adhesive fractures between the cement and the dental tissue were found. These failures might also have been related to a procedural error by the operators or to the excess layer of cement around the post, which may have provoked a change in the mechanical behaviour of the cement-post–composite resin complex. The resin cements that are supposed to provide the best adhesion (Ross et al 1991, Goldstein et al 1986) may represent a weak point in the system, mostly when a very thick and non uniform cement layer surrounds the post. It is reasonable to further detail the mechanical procedures that the operator may perform during the temporary phases and relate these to possible failures. It should be underlined that the cases showing the adhesive failures did not have the 2-mm ferrule of dentin considered to be important to obtain a high success rate (Assif et al 1991). In accordance with other clinical studies, the observed success rate of 98.3% was high and no root fractures

119 occurred. Therefore, it was possible to replace the failing restorations (Ferrari et al 2000). Other desirable properties of these posts are their biocompatibility and resistance to corrosion (Torbjörner et al 1996, Jockisch et al 1992). Fredrikson (Fredrikson et al 1998) reported no differences in the periodontal conditions between carbon fiber–treated teeth and controls. Radiographic examination of bone height measured from the apex to the bone margin mesially and distally showed differences on the mesial side, but not on the distal surface, between the treated and control teeth. Other in vitro studies have compared fiber posts with traditional metal posts to determine which system offers the best mechanical properties. Purton (Purton et al 1996) compared fiber posts and stainless steel root posts by three-point bending tests to derive the transverse modulus of elasticity of the posts. The carbon-fiber material was stiffer under transverse loading than stainless steel and thus appears to have adequate rigidity for its designed purpose. This higher rigidity allows smaller diameters to be used with equivalent strength, in accordance with the conservative principles. One weak point of the system is the bond between the post and the composite core material. The authors therefore suggested that a surface treatment or modification in configuration should be introduced. Drummod (Drummod 2000) evaluated the pullout (shear) strength of stainless steel posts and three different fiber posts and found no significant differences. With respect to flexure strength, all fiber post systems showed a significant decrease following thermocycling, probably because of the degradation of the polymer holding the fibers together and/or to the fibers themselves. The clinical relevance of this data still needs to be investigated. Relatively few clinical studies examining the success and failure of metallic posts have been reported. Sorensen (Sorensen et at 1984) reported an 8.6% failure rate resulting from post dislodgments, root fractures, or post perforations. Others reported a 6.5% failure rate after 10 years or more (Weine et al 1991) and an 8.3% frequency of failure after 2 to 3 years (Torbjörner et al 1995). Lewis (Lewis et al 1988) stated that failures of the post and core are more likely to occur within the first 3 years of cementation. A retrospective study (Ferrari et al 2000) evaluated the outcome of cast posts and cores and carbon-fiber posts after 4 years of clinical service. Ninety-five percent of the teeth restored with fiber posts showed clinical success, 3% were excluded, and 2% showed endodontic failure. Among the teeth restored with cast posts, 84% showed clinical success, 9% showed root fracture, 3% showed

120 endodontic failure, 2% had dislodgment of the post or crown, and 2% were excluded. Statistical evaluation has thus indicated that carbon-fiber posts are superior to conventional cast posts. In accordance with this study, the failures recorded with fiber posts were more benign. When a vertical fracture occurs, the entire element must be extracted. When finalized with all-ceramic crowns, the strong demand for a post-and-core complex with good esthetic results has guided both researchers and manufacturers toward the introduction of restoring systems that meet these requirements. According to a previous study, the clinical behavior of carbon-fiber posts and quartz-fiber posts is equivalent (Chalifoux 1998). To determine how much the post aspect will influence light transmission under the thickness of the ceramic, the following guidelines can be used (Vichi et al 2000). With a 2-mm ceramic thickness, color differences are clinically irrelevant, while with a ceramic thickness of 1.5 mm, the color differences are clinically visible in some cases and detectable only with a spectrophotometer in others. With a ceramic thickness of less than 1.5 mm, the aspect of the post-and-core restoration influences the all-ceramic crown in a manner that may be clinically unacceptable. The fiber post system offers a time savings, simple clinical procedures, and reliable results. Moreover, the technique is less invasive than other post systems because of the shorter length required, and thus the apical seal can be left around 4 mm (Goerig et al 1983a, Goerig et al 1983b). In cases of endodontic failures, it is possible to remove the post with the specific bur (Sakkal 1996). It is obvious that the clinician must follow the manufacturer’s instructions while treating the remaining dental tissues. The use of a rubber dam is imperative while performing the restoration. The combination of good mechanical performance with satisfactory esthetics may be a good starting point toward the improvement of routine dentistry and toward predicting success. We are awaiting future evaluations of these encouraging data. Within a 30-month period, 205 Æstheti-Plus quartz-fiber posts were used to restore 180 teeth with clinical success. The three failures recorded represented 1.7% of treated teeth. All three failures occurred during the temporary phases. The cohesive fracture and two adhesive fractures involved only the post-and-core restoration. No root or post fractures occurred. In the case of failure, it was possible to replace the restoration without losing the element.

121 Table 1 Distribution of Treated Teeth According to Type Central Lateral

Jaw Central Lateral Canines Premolars Molars incisor incisor

Maxilla 43 17 28 24 8

Mandibole 9 11 16 8 16

Both 52 28 44 32 24

Fig 1 Æstheti-Plus quartz-fiber post cemented in a maxillary right central incisor.

Fig 2 Completed core buildup.

References

Assif D, Pilo R, Marshak B. Restoring teeth following crown lengthening procedures. J Prosthet Dent 1991;65:62–64. Chalifoux PR. Esthetic restoration of endodontically treated teeth: Factors that affect prognosis. J Esthet Dent 1998;10:75–83. Dallari A, Rovatti L. Six years of in vitro/in vivo experience with Composipost. Compendium 1996;17:57–63. de Rijk WG. Removal of fiber posts from endodontically treated teeth. Am J Dent 2000;13:19b–21b. Drummond JL. In vitro evaluation of endodontic posts. Am J Dent 2000;13:5b– 8b. Duret B, Reynaud M, Duret F. Un nouveau concept de reconstituction corono- radiculaire: Le Composipost (1). Chir Dent France 1990;540:131–141.

122 Duret B, Reynaud M, Duret F. Un nouveau concept de reconstituction corono- radiculaire: Le Composipost (2). Chir Dent France 1990;542:69–77. Ferrari M, Vichi A, García-Godoy F. Clinical evaluation of fiberreinforced epoxy resin posts and cast post and cores. Am J Dent 2000;13:15b–18b. Ferrari M, Vichi A, Mannocci F, Mason PN. Retrospective study of the clinical performance of fiber posts. Am J Dent 2000;13:9b–13b. Fredrikson M, Astback J, Pameius M, Arvidson K. A retrospective study of 236 patients with teeth restored by carbon fiber reinforced epoxy resin posts. J Prosthet Dent 1998;80:151–157. Goerig AC, Mueninghoff LA. Management of the endodontically treated tooth. Part II: Technique. J Prosthet Dent 1983;49:491–497. Goerig AC, Mueninghoff LA. Management of the endodontically treated tooth. Part I: Concept for restorative designs. J Prosthet Dent 1983;49:340–345. Goldstein GR, Hudis SI, Weintraub DE. Comparison of four techniques for the cementation of posts. J Prosthet Dent 1986;55: 209–211. Goodacre CJ, Spolnik KJ. The prosthodontic management of endodontically treated teeth: A literature review. Part 1: Success and failure data, treatment concepts. J Prosthodont 1994;3:243–250. Jockisch KA, Brown SA, Bauer TW, Merritt K. Biological response to chopped- carbon-fiber-reinforced peek. J Biomed Mater Res 1992;26:133–146. Lewis R, Smith BG. A clinical survey of failed post retained crowns. Br Dent J 1988;165:95–97. Morgano SM, Milot P. Clinical success of cast metal posts and cores. J Prosthet Dent 1993;70:11–16. Purton DG, Payne JA. Comparison of carbon fiber and stainless steel root canal posts. Quintessence Int 1996;27:93–97. Ross RS, Nicholls JI, Harrington GW. A comparison of strains generated during placement of five endodontic posts. J Endod 1991; 17:450–456. Sakkal S. Carbon-fiber post removal technique. Compend Contin Educ Dent Suppl 1996;(20):86S. Sorensen JA, Martinoff JF. Clinically significant factors in dowel design. J Prosthet Dent 1984;52:28–35. Torbjörner A, Karlsson S, Ödman PA. Survival rate and failure characteristics for two post designs. J Prosthet Dent 1995;73:439–444. Torbjörner A, Karlsson S, Syverud M, Hensten-Pettersen A. Carbon fiber reinforced root canal posts. Mechanical and cytotoxic properties. Eur J Oral Sci 1996;104:605–611. Trabert KC, Cooney JP. The endodontically treated tooth. Restorative concepts and techniques. Dent Clin North Am 1984;28: 293–951. Vichi A, Ferrari M, Davidson CL. Influence of ceramic and cement thickness on the masking of various type of opaque posts. J Prosthet Dent 2000;83:412–417. Weine FS, Wax AH, Wenckus CS. Retrospective study of tapered, smooth post system in place for 10 years or more. J Endod 1991;17: 293–297.

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124

Chapter 11 summary and conclusions

Until now, clinical application of dental restorations to restore missing posterior teeth could only be performed using conventional metal systems because of high mechanical loading in this area. The resin-bonded fixed partial denture (FPD) is a treatment alternative for replacement of missing teeth when conservation of tooth structure is needed (Freilich et al 1998). Currently, alternative systems like fibre- reinforced composite (FRC) dental materials, are recommended for their ability to withstand these mastication forces. Fibre-reinforced materials combine the basically different mechanical properties of fibres and a matrix, in which the fibres are embedded. The fibres demonstrate high tensile strength, a high tensile modulus, and low shear strength, while the matrix is characterized by high toughness. In an optimum fibre-reinforced material, the tensile strength of the fibre is combined with the high toughness of the matrix (Vallittu et al 1999a, Vallittu et al 1999b). Fibre- reinforced technology is used wherever high stress occurs and low weight is required, such as in the aeronautical and shipbuilding industries. Numerous attempts have been made to develop ceramic systems that eliminate metal infrastructures and provide optimal distribution of reflected light. Currently clinicians have an increasing range of ceramics capable of delivering high quality aesthetic restorations to choose from for many clinical indications. New ceramic systems involve reinforced ceramic cores through dispersion with leucite (Kon et al 1994, Seghi et al 1995, Denry et al 1996, Mackert et al 1996, Mackert et al 2000), glass infiltration into sintered alumina (Al2O3) (Probster et al 1994, Sadoun et al 1994), the use of high-purity alumina (Andersson et al 1993) or zirconium dioxide (zirconia, ZrO2) (Piconi et al 1999).

Conclusions and recommendations

The following conclusions and recommendations may be drawn from our basic and clinical evaluations on the use of FRC and all ceramic systems applied in partial restorations:

125 1) Excluding the therapy with dental implants, inlay fixed partial dentures represent the most conservative treatment for the replacing of the missing tooth 2) The design of the FRC framework can play important role in supporting the layering material in a continuous manner. Vestibular and buccal FRC extensions in the pontic element can increase the bonding area between the framework and resin composite as well as hold the veneer material better during occlusal loading. 3) The flexibility of the framework may play an important role in the marginal adaptation of IFPDs and more rigid materials could transfer the stress to the margin to a smaller degree than flexible materials 4) The different arrangement of the glass fibers can increase the fracture strength of FRC three-unit bridges and IFPDs. Increased fracture strength could be useful in case of long span framework or short clinical abutments 5) fiber reinforced composites exhibit good overall mechanical properties and the related failure modes are usually more conservative and favorable when compared to the traditional metal-ceramic three unit bridges. 6) In short observation period the IFPDs in combination with a 3-step adhesive demonstrated good clinical service but we need more observations in order to create a sound basis for the final assessment of IFPDs 7) Longer observation periods and comparisons with new reinforced ceramic materials will help to identify the most suitable choice of material for IFPDs

References Kon M, Kawano F, Asaoka K, Matsumoto N. Effect of leucite crystals on the strength of glassy porcelain. Dent Mater 1994;13:138–47. Seghi RR, Sorensen JA. Relative flexural strength of six new ceramic materials. Int J Prosthodont 1995;8:239–46. Seghi RR, Denry IL, Rosenstiel SF. Relative fracture toughness and hardness of new dental ceramics. J Prosthet Dent 1995;74:45–50. Denry IL, Mackert Jr. JR, Holloway JA, Rosenstiel SF. Effect of cubic leucite stabilization on the flexural strength of feldspathic dental porcelain. J Dent Res 1996;75:1928–35. Mackert JR, Russell CM. Leucite crystallization during processing of a heat-pressed dental ceramic. Int J Prosthodont 1996;9:261–5.

126 Mackert Jr JR, Williams AL, Ergle JW, Russell CM. Water-enhanced crystallization of leucite in dental porcelain. Dent Mater 2000;16:426–31. Probster L, Diehl J. Slip-casting alumina ceramics for crown and bridge restorations. Quintessence Int 1992;23:25–31. Sadoun M, Asmussen E. Bonding of resin cements to an aluminous ceramic: a new surface treatment. Dent Mater 1994;10:185–9. Andersson M, Oden A. A new all-ceramic crown—a dense-sintered, high purity alumina coping with porcelain. Acta Odontol Scand 1993;51:59–64. Piconi C, Maccauro G. Zirconia as a ceramic biomaterial. Biomaterials 1999;20:1– 25. Sadoun M, Asmussen E. Bonding of resin cements to an aluminous ceramic: a new surface treatment. Dent Mater 1994;10:185–9. Freilich MA, Duncan JP, Meiers JC, Goldberg AJ. Preimpregnated, fiber- reinforced prostheses. Part I: basic rationale and complete coverage and intracoronal fixed partial denture designes. Quintessence Int 1998;29:689-696.

Vallittu PK. Flexural properties of acrylic resin polymers reinforced with unidirectional and woven glass fibers. J Prosthet Dent 1999a;25:100-105. Vallittu PK. Prosthodontic treatment with a glass fiber-reinforced resin-bonded fixed partial denture: a clinical report. J Prosthet Dent 1999b;82:132-135.

List of papers part of this thesis

Monaco C, Ferrari M, Miceli GP, Scotti R. Clinical Evaluation of Fiber-Reinforced Composite IFPDs. 2003 Int J Prosthodont 16:319-325.

Monaco C, Miceli GP, Scotti R. Die mit dem neuen, mikrogefüllten Komposit- Material SR Adoro verblendete Inlay-Brücke. Quintessenz Zahntech 29,3,292-305 (2003).

Malferrari S, Monaco C, Scotti R. Clinical evaluation of teeth restored with quartz fiber-reinforced epoxy resin posts. 2003 Int J Prosth 16;39-44.

Monaco C, Ferrari M, Caldari M, Baldissara P, Scotti R. Randomized controlled trial of Fiber-Reinforced Composite Inlay Fixed Partial Dentures: two-year results. Int J Prosth 2006, n press.

Monaco C, Krejci I, Bortolotto T, Perakis N, Ferrari M, Scotti R.

127 Marginal adaptation of one Fiber Reinforced Composite and two different all- Ceramic Inlay Fixed Partial Denture Systems. Int J Prosth 2006, in press.

Marginal adaptation of one Fiber Reinforced Composite and two different all- Ceramic Inlay Fixed Partial Denture Systems. Int J Prosth 2006, in press.

Baldissara P, Valandro LF, di Fiore P, Monaco C, Ferrari M, Bottino MA, Scotti R.

Fatigue test in shear: its effect on bond of a glass-infiltrated alumina ceramic to human dentin, using different luting procedures. J Adhes Dent 2006, in press.

List of abstract part of this thesis

Monaco C, Ferrari M . Randomized clinical trial of inlay fixed partial dentures . Abstr 585 119CED-NOF of the IADR meeting Amsterdam 14-17 september 2005.

Monaco C. Adhesive inlay bridges with FRC: clinical and laboratory investigations. Abstr SO460C 119CED-NOF of the IADR meeting Amsterdam 14-17 september 2005.

C. Monaco, P. di Fiore, P. Baldissara, R. Scotti. Fatigue resistance of in- Ceram/Dentin bonding: a comparative study. 2003 J Dent Res 82. Special issue B Abstr 1462.

Monaco C, Baldissara P, Caldari M, Scotti R. Six-month evaluation of post operative sensitivity in IFPDs. J Dent Res Abstr 579. Honolulu 2004

Baldissara P., Melilli D, Monaco C, Ciocca L. Fatigue resistance of fiber posts and different build-up materials. J Dent Res Abstr 579. Honolulu 2004.

Baldissara P, Quadrelli M, Monaco C, Scotti R. E-Modulus and Flexure Strength of FRC: Introducing Boron Fibers. Abstr 372 119CED-NOF of the IADR meeting Amsterdam 14-17 september 2005.

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