Metal-Free Inlay-Retained Fixed Partial Dentures

Metal-free inlay-retained fixed partial dentures

Daniel Edelhoff, Dr Med DentVHubertus Spiekermann, Prof Dr Med, Dr Med Dent^/ MuratYildirim, Dr Med Dent^

Objective: The treatment procedures used in conjunction with two different mstal-free restorative systems are illustrated on the basis ot clinical examples. In addition, a report en Ihe initial clinical findings is provided. Method and materials: Metal-free restorative materials are opening doors to new preparation methods because ct their ciose link to the adhesive cementation technique. As a resuit of the deveiop- ments over the past few years, various metal-free systems that can be used to fabricate short-span fixed partiai dentures (FPD) are now availabie. Certain guidelines, however, must be observed in the process. Because of their minimai invasiveness, inlay-retained FPDs offer an interesting soiution in cases where the residuai dentition exhibits low caries activity. Since the beginning of 1997, a tctal cf 23 metal-free iniay- retained FPDs made of twc different types of framework material (11 of high-strength pressed ceramic and 12 cf fi be r-reinfcreed ccmposite) have been examined in a clinical study. Results: One in lay-retained FPD made cf pressed ceramic had tc be replaced because of a fracture. Because the materials have only been on fhe market fcr a short time, long-term results are not yet available. Conclusion: This type of restoration provides exceilent esfhefics and reduced invasiveness compared wifh complete crown-retained FPDs, although indications are limited by the special mechanical properties o( the material. (Quintessence Int 2001:32:269-281)

Key words: adhesive technique, fiber-reinforced composites, high-strengfh pressed ceramics, inlay-retained fixed partial dentures, tooth-coicred restorative materials, tooth-preserving preparation techniques

complete crowns are preferred as the denture retainer. CLINICAL RELEVANCE: Two new types of materials Partial restorations in the form of partiai crowns, provide the potential for fabrication of metai-free inlay- inlays, and overlays are recommended as retainers in refained fixed parfial dentures wifh the advantages of the restoration of small gaps in caries-resistant denti- preservation of foofh sfrucfure and excellent esthetics. tion-^' In addition to facilitating the periodontal assessment,-"^ these types of retainers enable healthy tooth structure to be preserved.^ The removal of large enerally, metal-reinforced systems are the materi- parts of tooth structure is particularly problematic in Gals of choice for fabricating posterior fixed partial young teeth with an extensive pulp. Inlay-retained dentures (FPD) because of their reliability and dura- FPDs made of metal alloys are usually seated using bility.' Given the comprehensive range of indications, the conventional cementation technique and cements. Secondary caries and a loss of retention^'^ are the main causes of failure of these FPDs. Inadequately retentive preparation shapes and insufficient stability of the metal framework were perceived to have been contributing factors. As a result, more effective intra-

'Assistant Professor, Deparlment ot Prosthodontics, School of Dentistry. coronal retention with the help of boxes, grooves, and Medical Centre, University of Aachen, Aachen, Germany. pins was demanded.^•^•" These solutions, however, 'Protessor and Chairman, Departrrent of Prosthodontics, School oí mitigated the advantage of minimal invasiveness com- Dentistry, Wedical Centre. University of Aachen, Aachen, Germany. pared with complete-crown retainers. ^Associate Professor, Department cf ProsthoOontics. School of Dentistry. Restorations made of metal alloys are characterized Medical Centre. University of Aachen, Aachen, Germany. by certain basic disadvantages. The base metal compo- Reprint requests: Dr Daniel Edelhoft. c/o Dr J.A. Sorensen, Dental Clinical nents that form on the surface of the alloy during the Research Center, Oregon Health Sciences University, 611 Southwest Campus Drive, Portlancf, Oregon 97201-3097. E-mail; edelhotteohsu.edLi metal-ceramic fusing process may have a negative

269 • Edelhofíetal

Fig 1 Metal-free inlay-retained FPD fabricated witfi a higfi- Fig 2 Framework fabrication for an FPD using a liber-feinlorced strengtfi pressed ceramic composite.

made of these materials are not as strong as tbose that are metal-supported because of tbeir particular mecbanical properties," To achieve adequately strong dental restorations, therefore, certain modifications arc necessary in the preparation, fabrication, and cementation methods. Tbe preparation geometry of an inlay retainer offers favorable prerequisites for tbe adbesive cementation technique, Tbe 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. In the adhesive tecbnique, conditioned enamel surfaces are considered to mediate a bond just as reliably as conditioned Fig 3 Light transmission of a metal-free FRC FPD. ceramic surfaces,^''-^'* The increased inclusion of enamel promotes tbe bond to dentin, which still pre- sents certain problems hecause of the diiïerent structures,^'-^^ Adhesive cementation eould offer one of the most effective ways of countering tbe loss of retention, which is one of the most frequenf causes of failure of conventional inlay-retained FPDs, effect on tbe adjacent soft tissue,^'''^ In addition, the Tbe purpose of this article is to illustrate the proce- opaque, darldsb appearance created by certain metal dures related to the placement of inlay-retained FPDs denture retainers in tbe abutment teeth is considered with clinical examples and to provide a report ahout to be unattractive,'^ Consequently, alternative materi- the initial clinical results. als sucb as bigb-strength pressed ceramics'^'^ (Fig 1) and fiber-reinforced composites (FRC)"'' (Fig 2) bave achieved a certain degree of popularity in restorative METHOD AND MATERIALS dentistry today. Metal-free materials sucb as high-strength pressed Indications/contraindications ceramics exhibit outstanding corrosion resistance. Furthermore, less plaque accumulates on tbese sur- The indications have to be strictly observed because of faces than on those of other dental m ate rials, 2"-^' The tbe special properties of metal-free materials. As a esthetic properties of these systems must be attributed result, careful assessment and planning prior to begin- to the high translucency of tbe materials and the fact ning the prosthodontic treatment tneasures are requi- that tbe restorations are entirely fabricated of tooth- site. Furthermore, the following prerequisifes must be colored materials, thereby achieving a high degree of met if successful results are to be achieved with metal- light transmission^^ (Fig 3), However, restorations free in lay-retained FPDs:

270 Volume 32, Number 4, 2001 • EdelhofI et ai

• Good oral hygiene • Low susceptibility to caries • Parallel alignment of abutment teeth • Immobility of abutment teeth (degree of loosening = 0) • Minimum height of abutment teeth > 5 mm [connector thickness) • 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 FRC materials are used

Severe parafunctions, short clinical crowns (< 5 ram), 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 pretreated teeth are included in the preparation to stabilize them. Alternatively, the preparation for a complete crown should be considered.=" Metal-free inlay-retained FPDs must be adhesively cemented because of the lower pri- Fig 4 Possible indication for a metal-free mary friction compared with metal-supported systems. in lay-ret a med FPD. In previous orthodontic Existing therapy-resistant periodontopathologic com- treatment measures, tooth 37[18J was straightened. plaints as well as allergies to the components of dentin adhesives or luting composites, therefore, must be clas- sified as absolute contraindications. Gingival bleeding compromises the adhesive bond between the resin and the prepared tootb. In preparation for adhesive cemen- by tbe bydrodynamic effect of provisional materials tation, therefore, all signs of periodontal inflammation tbat demonstrate inadequate marginal seal."" Thus, should be eliminated. the most important factors^^-'" that cause postoperative In additioti to a thorough intraoral examination, sensitivity are prevented. The fact that the deferred radiographs (proximal caries, periodontium) of the procedure gives the adhesive system enough time to designated abutment teeth and irreversible hydrocol- bond to dentin is another favorahle side effect. Burrow loid impressions of both jaws for the model analysis et aP* showed that most of the tested dentin adhesive are recommended for evaluating these factors. Special systems achieved the highest hond strengths only after attention must be paid to generalized wear facets, the 24 hours, even though the immediate attainment of position of the antagonistic contacts, existing hyper- maximum bond strength is desirable because of the balances, the length of the clinical crown, the pontic polymerization shrinkage of the luting composite. In span, and the alignment of the abutment teeth [Fig 4). the described procedure, the adhesive dentin seal In addition, canine guidance must be ensured to pro- mediates a bond between tbe dentin and tbe luting tect the inlay-retained FPD from torsional stress. If it composite during tbe subsequent placement of tbe has not been establisbed, its reconstruction during tbe permanent restoration. In similar tecbniques (dual restorative procedures should be considered, bonding), this step has been sbown to increase the dentin bond strengths of various adhesive systems." Pretreatment Build-ups of considerable volume should be fabricated using highly flUedcomposite s of the latest gener- After the existing restoration has been removed and ation (eg, ZIOO, 3M Dental) and the adhesive tech- the caries carefully excavated, the prepared dentin is nique. Modern composite systems demonstrate more directiy sealed with a dentin adhesive used in combi- favorable properties'^-'" than other moldable tooth- nation with a thin coat of a low-viscosity composite colored build-up materials. In addition, tbey enhance-" (eg, Tetric Flow, Vivadent). The objective of this tech- the optical properties of the restorative material.^^ nique is to prevent contamination of dentin with bac- Moreover, an increase in the fracture resistance of teria and components of the impression and provi- ceramic inlays has been established in an in vitro sional cementation materials.="^ In addition, this examination in which composites were used as a sup- procedure reduces the masticatory sensitivity caused porting structure in the cavity.-'^

271 • Edelhoff et al

Fig 5 Prepreparation of abutment tootti Fig 6 Use of an oscillating instrument to Fig 7 Provisional restoration ol the inter- 35[20] as an inlay retainer. produce a standardized proximal box lacing dentai gap. The provisionai was labricated ttie pontic. The vertical dimension of the with the help oí a vacuum-formed template. abutment must be approximately 5 mm to ensure the required minimum thickness of the connector to the portic

Prefabricated tooth-colored zirconia oxide ceramic • Abutment teeth with a wide bucco-oral defect root posts are available for restoring endodontically (> 50%) as well as devitalized abutment teeth; pretreated teeth (eg, CeraPost, Brasseler, or inclusion of cusps in the preparation^" CosmoPost, Ivoclar).••^•''•' Inlay preparations in posten- • Divergence angle of the cavity of approximately 6 dodontically restored teeth, however, should be degrees avoided. A partial- or complete-crown preparation is preferred. First, the tooth is prepared for the inlay using diamond burs (Fig 5). Oscillating instruments (eg, Sonicsys Preparation Approx Point No. 4) are used to prepare the box facing the interdental space. They create a standardized space The preparation must take the specific requirements of for the connector to the pontic" (Fig 6). The cavity walls metal-free materials into account.'^ In this clinical and the enamel margins are subsequently finished using study, the ahutment teeth were prepared according to water-cooled, slightly conical Arkansas stones, which are the following guidelines: shaped according to the preparation instruments by rotating them against a diamond-coated surface (Dura- • 2-mm occlusal preparation depth (fioor of isthmus White stones type TC 1, Shofu).'^ Light pressure is to central groove) applied, and average rpms (blue rigbt-angle electric • 1.5-mm preparation depth of proximal box [shoul- handpiece) are used. In this context, it must be noted der with rounded internal angle) that tbe sealing of dentin is ensured and enamel margins • Isthmus width of 1.5 to 2 mm in premolars and of are free from composite residue of the restoration. A 2.5 to 3 mm in molars one-step technique using elastic materials is recom- • Proximal angle of the internal cavity surface to the mended for impression taking {eg, Permadyne, ESPE), enamel surface {100 to 120 degrees)''^ The provisional restoration is fabricated using transpar- • Minimum dimensions of connectors; 4 mm x 5 ent, reusable polyethylene-hased vacuum-formed tem- mm^ (corresponds approximately to a Sonicsys plates and a bis-GMA resin (eg, Protemp II, ESPE) {Fig Approx Point No. 4 [Iialtenbacb & Voigt] that is 7). This procedure combines two advantages: repairs are fully inserted into the cavity)"^ easy to carry out witb almost any composite system, and

272 Voiume 32, Number 4, 2001 • Edeihoft ef al

Fig 8 Try-in of a pressed ceramic frame- Fig 9 The preparation is cfeaned with Fig 10 fh preparation lor the adhesive work. In order to achieve the highest possi- rcfary brusfies and a tluoride-tree cleaning pfacement of a metal-free infay-retained ble strength of the restoration, fhe FPD paste foflowing absolute isolation with a rub- FPD fabricated ot a higfi-strength pressed retainers and the connectors are fabricated ber dam. ceramic, the contacf surfaces oí the infays of the fnigh-sfrength ffamewcrl< ceramic. are etched with hydrofluoric aoid (HF) for 20 Onfy fhe pontic is veneered at a fater stage. seconds.

the templates can be reused. The cavity must be tbor- ing resin (eg. Pattern Resin, GC) on tbe occlusal sur- oughly isolated during tbe fabrication procedure to pre- face of tbe pontic, Tbese stops merely touch the tips of vent a bond from forming witb tbe existing composite the stress-bearing antagonistic cusps (Fig 8). layer. As a result, eugenol-free composite-based provisional cementation materials sbould not be used. Placement

Try-in The restoration is placed according to the adhesive technique exclusively in conjunction with absolute iso- The framework of a bigb-strengtb pressed ceramic lation using a rubber dam. Following the isolation pro- inlay-rctained FPD is usually tried in. Fiber-reinforced cedure, provisional cement residues are removed from itilay-retained FPDs, bowever, arc completed immedi- the prepared cavities using pumice paste (Fig 9). The ately. The fit of tbe ceramic framework and the inlays use of hydrogen peroxide is contraindicated, because is cbecked in tbe oral cavity using a low-viscosity sili- nascent oxygen may inbibit the polymerization of the cone material. The ceramic framework should be luting composite to a certain extent in the adhesive stress free, and tbe inlays should demonstrate marginal cementation process. The final try-in of the finished integrity in tbe cavities. If tbe fit is inaccurate, tbe per- restoration should be conducted with glycerine paste forated parts of tbe silicone film are marked witb a tbat has the same shade as the luting composite. This lead pencil atid selectively groutid using water-cooled, procedure enables the final appearanee of the shade as bonded ceramic abrasives. The higb level of friction well as the correct shade of tfte cementation material that is common in metal-reinforced restorations must to be determined (eg, Variolink Try-In, Vivadent). he avoided to prevent tbe materials from being Once the restoration meets all of the functional and exposed to permanent crack-inducing tensile stress. To esthetic requirements, it is ready for adhesive cementa- achieve a very strong restoration, tbe denture retainers tion. For this purpose, the denture retainers are condi- atid tbe connectors must be made of tbe higb-strength tioned as follows. The contact surfaces of the pressed framework ceramic material.'' Only the pontic sbould ceramic inlays are etched with a bufiered bydrofiuoric be veneered. Tbe fine adjustment of tbe static occlu- acid (IPS Ceramic Etching Gel, Ivoclar; maximum 5% sion is achieved by placing small stops made of model- bydrofiuoric acid content) for 20 seconds [Fig 10). The

273 Edeihoff et ai

Fig 11 The contaC. surlaces ot the FPD Fig 12 A bw"id ng riGünt (silane) is applied retainer ot a metal-lree FPD made ot a fiber- to the üunditioned coniacl surfaces of the reinforced composite are conditioned using restoration foiiowing the pretreatment. a modified Rocatec method.

surfaces of restorations made of FRC materials, how- curing composite material (eg, Tetric Classic, Cavifil, ever, must be conditioned according to a modified Vivadent). The inlay-retained FPD is placed on the Rocatee procedure [only 1-bar pressure, llO-i^m grit, abutment teeth and seated in the cavities using ati 20-mm distance of the nozzle, vertical blasting angie, ultrasonic tip (eg, Sonicflex 2000 L, Sonicswing, 13-second treatment)-'^ (Fig 11). Following the drying Kaltenbach & Voigt) (Fig 16). This technique takes of the restoration, a silane coupling agent that will advantage of the thixotropic properties of the compos- condition the prepared tooth during the intraoral ite, which turn the material into a liquid when it is treatment measures is applied to the preconditioned exposed to high-frequency vibrations. As soon as the contact surfaces (Fig 12). This silane layer must not be tip is removed, however, the material reassumes its contaminated or exposed to moisture. The prepared heavy-bodied consistency.*' Because the operator is in tooth is thoroughly cleaned and dried with an air- control of the working time, excess material can be water syringe. The enamel margins of the cavity are removed easily and thoroughly. selectively etched with 37% orthophosphoric acid for Once the restoration is correctly in place, excess approximately 30 seconds (Figs 13 and 14). The dentin composite is removed with resin pellets and dental surfaces, which were conditioned in the pretreatment tape, while the restoration is held in place with a ball- phase, are wetted again with the bonding agent (dual shaped condenser. Subsequently, a glycerine ge! is bonding technique") (Fig 15). A compatible bonding applied to the tooth-resto ration interface to prevent agent is applied to the conditioned inlay contact sur- the formation of an oxygen-inhibited layer*^ (Fig 17). faces and subsequently to the prepared tooth. Initial curing from the occlusal aspect turns the com- During the following treatment steps, neither the posite into a jelly-like state after 10 to 20 seconds inlay-retained FPD nor the prepared tooth should be depending on the intensity of the curing light. At this directly exposed to operatory lights to prevent prema- stage, excess can be removed near the suicus with the ture polymerization. After a reaction time of 20 sec- help of a sealer (eg, SH 6/7, Hu-Friedy). The restora- onds, the bonding agent is blown to a thin layer with a tion must also be held in place during these steps. gentle stream of air. The next few steps are preferably Final curing must be conducted very carefully when carried out using the ultrasonic insertion (USI) tech- purely light-curing composite materials are used."** nique. Foiiowing enamel and dentin conditioning, the This step is influenced by the translucency of the cavities are filled with a highly viscous, purely light- restorative material'*"" For this purpose, the abutment

274 Volume 32, Number 4, 2001 Edelhoff el al

Fig 13 The first stage of the adhesive Fig 14 The phospfioric acid is carefully Fig 15 Conditioning of dentin surfaces piacemeni procedure involves selective removed using a mixture of water and air, using a dentin bonding agent After Ihe etching of the enamel areas for 30 seconds and the abutment teelh are dried. reaction lime, the Nquid film is carefully dis- with 37% phosphoric acid, persed to a thin layer with an air syringe.

teeth are exposed to a high-performance curing light^' placement of a dry retraction cord arc permitted. (approximately 600 mW/cm^; eg, Demetron Optilitx Alternatively, a rubber dam may be used to expose an 401 or 500, Demetron Research} from all sides adequate area around the prepared abutments (Figs 19 according to the instructions of Pesek et al," Each to 21), The purpose of these measures is to draw the side is exposed for 120 seconds. The effect of light- marginal gingiva away from the preparation margin, conducting interdental wedges should not he overesti- reduce the gingival fluid rate, and prevent components mated in this context. Nevertheless, these wedges are of the adhesive luting composite from penetrating into capable of somewhat enhancing the final light-curing sensitive areas of the epithelial and connective tissue process in the proximal region^^ (Fig 17), attachment during the placement procedure. Because of the limited curing depth associated with inlay-rctained FPDs featuring frameworks of more than 3 mm in thickness,^''^^ dual-curing (eg, Variolink INITIAL CLINICAL RESULTS II, Vivadent) or self-curing [eg, Panavia 21 TC, Kuraray) luting composites are recommended for the Since the beginning of 1997, 23 metal-free inlay- adhesive cementation of these restorations. Luting retained FPDs have been placed at our chnlc in the composites are available In a variety of shades. It course of a clinical study. Eleven of these FPDs were should be noted that composite materials (eg, FRC fabricated using a heat-pressed lithium disihcate glass materials) usually demonstrate a higher light absorp- ceramic (pressed ceramic; IPS Empress 2, Ivoclar), tion,''' The tooth-restoration interface is subsequently and 12 were made using an FRC material (Targis/ finished with tungsten-carbide finishers and polishing Vectris, Ivociar), In 4 cases (1 pressed ceramic and 3 pastes (eg. Composite Finishing System, Kerr). Narrow FRC FPDs), tbe inlay retainer was combined with a finishing strips (Sof-Lex Finishing and Polishing complete-crown retainer (Figs 19 to 27), The mean Systems, 1954 N, 3M Dental) are suitable for finishing period of service of fhe pressed-ceramic FPDs was 9,9 hard-to-reach proximal areas. Finally, the tooth- ± 3,4 months; that of the FRC FPDs was 15,3 ± 7,6 restoration interface is fluoridated (eg, Fluor Protecfor, months. During the first clinical recall, one absolute Vivadent) (Fig 18). failure (a completely new restoration was required) If the preparation margin is located in an isogingi- was recorded (status 12/99) in the form of a fracture val or intrasuicuiar area, relative isolation and the within the connector to the pontic of an inlay-retained

275 Edelhoff et al

Fig 16 Plaoement using the Ultrasonio Fig 17 Atter the excess material has been Fig 18 Peimanently piaced aii-ceramic Insertion [USi] technique. The cavities are removed, the tooth-iestoraiion interfaces are inlay-reiained FPD after finishing, polishing, filled with a highly viscous, purely light-cur- ooated with glycenne gel to prevent oxygen and fluoridation. The transitional areas of the ing composite material. The inlay-retained inhibition of the composite. In each case. natural toolh structure are clearly visible FPD is placed m its permanent position Ihe restoration is cured from all sides lor 120 because of the opaque appearance of the using an ultrasonic tip. seconds using a high-performance curing oeramic framework materials, light.

jvas prepared for an iniay retainer

276 Volume 32, Number 4, 2001 •Edelhoff et ai

Fig 22 Preparation for an FRC FPD (teeth Fig 23 Compieted FRC FPD prier to the 35[20] to 38[17]). Note the inciination of the adhesive piaoement with a low viscous axis of abutment 38, which has been pre- dual-curing luting composite. pared for a partiai crown retainer.

Fig 24 Giycerine gei was appiied to the Fig 25 Permanentiy piaced FRC FPD after tooth-restoration interface after the removai finishing and polishing. The transitions of the of eKcess using resin peliets and dental natural tooth structure are smoother than floss. those achieved with high-strength pressed ceramio.

277 •Edeihoft et ai

Fig 26 Preoperative situation showing severaf amaigam restora- Fig 27 Resuit foifowing the placement of an FRC FPD (teetii 35 tions requiring re pfacement. to 38) and indirectfy tabricated composite restorations in leetfi 34[31],45[29],and46[30|,

DISCUSSION

The integrafion of metal-free inlay-retained FPDs into the range of conservative restorative opfions requires that a distinction be made witb regard to adhesive FPDs for the posterior region. Adhesive metal-reinforced FPDs with groove preparations on the wing- shaped retainers demonstrate a remarkahle long-tertn success rate if they are placed according to a strict technical procedure.''^•^'' Restorations of this kind require minimally invasive preparation and are thus indicated in caries-free and restoration-free abutmetit teetb. These classic design principles cannot be Fig 28 Absoiute faiiure of an iniay-retained FPD fabricated of a directly applied to adbesive FPDs made of metal-free high-strength pressed ceramic. Because tfne verticai dirnension of materials, because more removal of tbe tooth structure the ciinicai crown was insufficient, tiie required dimensions for fhe is necessary due to the required thickness of the connectors to ffie pcntic (5 mm) couid not be achieved. Less tiian 3 mm was avaiiabie verticaiiy. framework materials. In many cases, therefore, wing- shaped retainers cannot be used, because space is limited and dental enamel has to be preserved. If the requirements of tbe material are taken into considera- tion, an inlay-like retainer seems to be more suitable for metal-free adhesive FPDs in the posterior region,'' FPD after 11 months in situ. An analysis of the frag- As a result, the difference compared with metal-free ments of the pontic showed that the specified tnini- inlay-retained FPDs is minimal and chiefly applies to mum connector dimensions of 20 mtn^ near the molar the dimensions of the inlay retainer. had not been ohserved (Fig 28). Tbe components of To date, reliable data regarding the long-term suc- the framework material proved to be very difficult to cess of inlay-retained FPDs are unavailable. After 3 remove from the inlay cavity because of the hardness years of clinical service, 3-unit, minimally invasive, of the lithium disilicate ceramic and the almost indis- nonreinforced inlay-retained FPDs demonstrated a tinguishable transition between tbe material and tbe survival rate of only 58%.'^ By contrast, bonded glass tootb structure. fiber-reinforced composite inlay FPDs were consid- From an estbetic point of view, tbe transition ered clinically successful at tbe 1-year examination.^' between the restoration and tbe tooth structure was A I3.50/0 failure rate was recorded after 3 years of ser- more pronounced in inlay-retained FPDs made of vice in tbe recall examinations of 37 inlay-retained pressed ceramic tban in restorations made of FRC FRC FPDs tbat bad been placed in a private materials (see Figs 18 and 25), pracfice," Adbesive FPDs fabricated of an infiltrated

278 Volume 32, Number 4, 2D01

W J • Edelhcff et ai • aluminum oxide ceramic"-*" clearly exhibited lower free materials if retentive elements are provided has survival rates than the metal-supported versions. heen shown in the clinical application of a "slice" Because these results cannot be directly applied to preparation,'^ which does not involve any type of inlay-retained FPDs, a differentiated evaluation of the retention. In a clinical study of denture retainers pre- availahle data on conventional inlay-retained FPDs pared in this way, 10.5% of the cases demonstrated a should be conducted. Eichner'^' considers inlay- loss of retention after oniy 4 months.'" retained FPDs to be merely an initial phase in the per- Despite the developments of the past few years, the manent restoration of small interdental gaps, which low strength of the metal-free materials compared may be restored with a conventional complete crown- with metal-supported materials remains a critical retained FPD at a later stage (second phase). This aspect. FPDs fabricated of these materials therefore view must take into account the higher rate of failure require large connectors (up to 20 mm^) from the den- compared with FPDs retained by complete crowns. ture retainer to the denture itself to prevent premature Inlay-retained FPDs made of gold alloys, which fractures. The vertical dimension of these connectors were placed using conventional cements, demon- contributes in the third power to the stability of tbe strated a failure rate between 28.1% (after a mean connector to the pontic; the horizontal extension only period of service of 9 years^) and 46.4% (after a period has a linear effect.*' To accommodate these connec- of service of 2.5 to 9 years'). Secondary marginal tors, the abutment teeth must be adequately high (see caries and loss of retention were recorded as the main Contraindications). As a result, the indication for this causes of failure.^ After 10 years in situ, the secondary form of restoration is restricted. If the required thickness of the connector is not observed, severe failures caries rate under single inlay restorations was 7% will occur; the inlay-retained FPD made of pressed higher than under single complete-crown restor- ceramic that failed in our study is an exampie (Fig 28). ations.' This rate does not include the development of new caries lesions. To prevent the reduced strength of metal-free restora- Erpenstein and Diedrich'' found new caries lesions, tive systems from being a limiting factor in their applica- which did not develop in connection with secondary tion compared with metal-supported systems, the devel- caries, on the remaining tooth surface in 6.1% of teeth opment of stronger metal-free systems tbat demonstrate restored with partial crowns. A heightened susceptibil- the same favorable light-optical properties of the current ity to caries, therefore, is a clear contraindication for materials would be desirable in the future. this type of restoration. The following factors are considered to be responsi- ble for tbe loss of retention: mobility of the abutment CONCLUSIONS teeth because of elastic jaw deformation,*"- loosening of teeth because of periodontal factors, and inade- The following conclusions regarding adhesively quate preparation of teetb.^' Furthermore, the conven- cemented inlay-retained metal-free FPDs can be tional luting cements used in the classic method are established to date; not quite capable or entirely incapable of forming a ffiicroretentive or a specific adhesive bond to the 1. This type of restoration provides excellent esthetics ground tooth structure and the restorative material and reduced invasiveness compared with complete (alloy). Theoretically, the additional adhesive support crown-retained FPDs. provided by mechanical retention should prevent the 2. A retentive preparation design shouid be realized loss of retention." Specific bonding to the alloy sur- to provide mechanical suppotl. face" and the tooth structure-'''^' has been successfully 3. The indications are litnited because of the special carried out for a number of years in tbe adhesive FPD mechanical properties. technique."'* 4. The removal of a fractured restoration made of In a clinical study, inlay-retained FPDs fabricated high-strength ceramic is complicated because of the of high gold alloys that were placed using this tech- hardness and the tooth-like color of the material. nique demonstrated a failure rate of a mere 3.9% after 5. To date, no long-term results are availabie. 5 years.^^ Because a reliable adhesive bond can be generated to metal-free materials such as ceramics,^*''*" a similarly positive influence on the retention behavior ACKNOWLEDGMENTS is expected in bonded metal-free inlay-retained FPDs, In another clinical study, glass-ceramic inlays proved The authors would like to thank Ms Julia Gatitenbrink, MDT, and Mr Andreas Rübben, DT, of Aachen, Germany, as well as Mr Kurt to be highly reliable during a mean period of service of Fiedler, MDT, of Ellwangen, Gernianj', for the fabrication of the 6 years.** The fact that the adhesive technique can FPDs. only be successfully used in conjunction with metal-

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