Journal of Advanced Clinical & Research Insights (2021), 8, 13–18

REVIEW ARTICLE

Indirect resin composite – A literature review R. Agathian1, P. S. Manoharan2*, E. Rajkumar E2

1Department of Prosthodontics, and Bridge, Indira Gandhi Institute of Dental Sciences, Puducherry, India, 2Department of Prosthodontics, Indira Gandhi Institute of Dental Sciences, Puducherry, India

Keywords: Abstract Composite inlays, Indirect resin composite, Esthetic dentistry is one of the most dynamic and challenging branches. With increasing Laboratory composite esthetic demands, the use of composite has become widespread. From the beginning

Corresponding author: of indirect composite resin usage, several advances in composites have been developed P. S. Manoharan, Department of in dentistry. Later, with improved modifications in their composition, structure, and Prosthodontics, Indira Gandhi Institute of polymerization technique had led to the innovation of the second-generation indirect Dental Sciences, Puducherry, India. resin composites (IRCs). IRCs provide enhanced mechanical property, better esthetic E-mail: [email protected] performance, decreased polymerization shrinkage, and repairability. Owing to these features, IRCs have been used broadly in various clinical applications. Hence, the aim of Received: 16 January 2021; this article is to review and explore the properties and advances in IRCs. Accepted: 18 February 2021 doi: 10.15713/ins.jcri.322

Introduction microleakage associated with direct composite has not been eliminated thoroughly by any method. Composites are used routinely in clinical practice. They had To address these challenges, IRC was introduced. IRC shows been introduced into the field of dentistry in 1940s to overcome improved physical properties such as wear resistance, hardness, the drawbacks of acrylic resins which replaced silicate cement. very minimal polymerization shrinkage, color stability, and formulation has been continuously biocompatibility when it is subjected to heat along with visible evolving since the introduction of Bis-GMA into dentistry spectrum light, vacuum, or pressure.[3] They are routinely used by Bowen in 1962. The clinical application of resin-based to restore teeth with extensive coronal loss. composites has been expanded due to the development of the When compared to composite resins, ceramic material is physical and optical properties of the composites. Composite more prone to fracture and susceptible to tensile stresses but is resins used in dental restorations can be broadly classified into resistant to compressive forces. Better stress distribution seen direct and indirect resin composites (IRCs). IRCs otherwise in composite resin than ceramic in Class II cavities. For larger known as prosthetic or laboratory composites. IRCs provide a defects, composite inlays are usually chosen for restoration.[4] better esthetic alternative for large posterior restorations.[1] Indirectly fabricated IRC restoration allows visual In the beginning, composites were used as an anterior examination of proximal contacts, marginal adaptation, anatomic restorative material. Thereafter, with technological form, and less polymerization shrinkage when compared with [5] development in composite resin, restoration of posterior teeth direct composite technique. with composite had begun. Failure of clinical restoration with posterior direct composites was mainly due to poor wear Characteristic Features of IRCS resistance, inherent color instability, polymerization shrinkage, Control of polymerization shrinkage microleakage, and post-operative sensitivity.[2] Although modern direct composites provide extraordinary mechanical Polymerization shrinkage is less in IRC when compared to and optical property, their use in large posterior restorations the direct composite due to additional curing with light, heat, is still questionable as polymerization shrinkage remains a and pressure which takes place extra orally. This results in a major dispute. Innumerable approaches have been arrived restoration which is slightly smaller than the preparation due to overcome these deficiencies, but the problem of marginal to polymerization shrinkage, but this space is compensated by

Journal of Advanced Clinical & Research Insights ● Vol. 8:1 ● Jan-Feb 2021 13 Agathian, et al. Indirect resin composite the luting cement in IRC restorations. The only shrinkage that procedures. Hence, it is hard to modify or add extrinsic color to occurs with IRC restoration is equivalent to that of the thin layer these restorations at the chairside. of luting resin cement during cementation. Luting Secondary polymerization The thin layer of luting resin cement which is applied The major disadvantage of direct composite restoration is during the luting procedure is liable for shrinkage at the tooth- that, even though well cured, it does not undergo complete restoration interface. polymerization and only 55–65% degree of conversion (DC) occurs. As indirect composite undergoes further polymerization by heat, intense light and/or pressure in addition to light cure, it Indications of IRC produces a greater degree of polymerization; hence more amount 1. of resin is polymerized. This increases the DC to about 75–81%, 2. Laminate veneers [6] which gives higher strength and hardness to the composite. 3. Jacket crowns 4. Implant-supported restorations Resistance to occlusal wear 5. Patients with bone loss and poor periodontal support Enhanced physical property and effective polymerization make requiring occlusal coverage IRC increased resistant to occlusal wear than direct composites 6. Full coverage crowns with value <1.5 μm/year. 7. Fiber-reinforced bridges/retainers[6] 8. Anterior indirect restorations due to , Improved control over contacts and contours abrasion, fluorosis, numerous aesthetically unsatisfactory [7] As fabrication of IRC restorations is done outside the oral cavity, superficial restorations, and diastemas. it gives better control over the material and an excellent proximal contour and contact area, and occlusal morphology can be Contraindications of IRC achieved greatly which makes them superior to direct composites. 1. Teeth with heavy wear and tear due to temporomandibular Enhanced physical properties joint and occlusal disharmony Due to increased content in IRC than direct composites, 2. Patients with parafunctional habits IRC has better physical properties such as strength, wear, 3. Inability to isolate the working area since luting of IRC hardness, and marginal integrity, thereby increasing the longevity restoration is technique sensitive. of the IRC restoration. Classification of IRCs High esthetics A. Classification based on the generations and type of fillers IRC restoration shows better retention and excellent esthetics 1. Based on generations over a long period of time when compared to direct composite a. 1st generation materials restoration as it is polished in the laboratory. Color combinations b. 2nd generation materials can be achieved for teeth and gingival portion with IRCs, which c. Next-generation materials helps the clinician to obtain an optimal white and pink esthetic 2. Based on type of fillers outcome.[6] a. Micro filled composite b. Fine hybrid composite Disadvantages of IRC Restorations c. Coarse hybrid composite Expensive B. Classification based on fabrication method a. Direct-indirect/semi-indirect method There is additional laboratory cost involving impression and b. Indirect fabrication method temporization, leading to the increased cost to the patient. First-generation IRCs Increased tooth structure reduction In 1980, Touati and Mormann et al introduced the first To create a path of insertion and removal, IRC restorations require generation of IRC. Their composition was similar to that of the more tooth reduction when compared to direct composites. direct composite resins. Examples are SR-Isosit Inlay system, Coltene Brilliant, Visio-gem (ESPE), Dentocolo (Kulzer), Difficult for modification Concept (Ivoclar). IRC restorations are manufactured in the laboratory and SR Isosit system is a homogenously filled composite luted into the prepared cavity after the finishing and polishing containing 55% by weight of colloidal silica with 20% radiopaque

14 Journal of Advanced Clinical & Research Insights ● Vol. 8:1 ● Jan-Feb 2021 Indirect resin composite Agathian, et al. lanthanum fluoride. Brilliant is a fine particle size (0.5 mm) curing system. They contain fillers such as aluminum oxide, hybrid composite and concept is a highly filled microfilled , and ceramic microfilaments.[10] Available composite. shades are cervical, body, incisal, translucent, and opaque 7. Sculpture plus (Pentron) is a nano-hybrid IRC. Polymerization Drawbacks of first-generation IRCs is done under pressure both before and during light cure with 1. Poor clinical performance the help of automatic light cure device. It is available as neck, 2. Inadequate bond between organic matrix and inorganic fillers body, Opaceous body, and incisal pastes 3. Poor wear resistance 8. TESCERA ATL (BISCO INC) contains a highly filled 4. Higher incidence of bulk fracture. hybrid dentin material. Body and incisal material consist of reinforced microfiller. Light cup and heat cup underwater Second-generation IRCs are used for polymerization. They show the advantages of both composite resins and porcelains. Improved clinical The second-generation IRCs were introduced in the mid- performance is due to increased concentration of the 1990s with improvements in their compositions and different microfiller particles curing mechanisms. The development of second-generation 9. Paradigm MZ100 (3M ESPE) contains ultrafine zirconia- composites came into role because of the clinical failures that silica fillers synthesized by a patented sol-gel process persist with the first-generation composites and the limitations 10. Vita Zeta LC (Vita Zahnfabrik) contains multiphase feldspar faced with ceramic restorations. frits and silicon dioxide filler. High translucent obtained as a Structure and composition result of natural refraction is ensured by the nanofillers 11. Pearleste E2 (Tokuyama Dental Corp) has Silica-Zirconia They contain “microhybrid” ceramic fillers of diameter and Silica-titania fillers 0.04–1 µm, with double the amount of filler content, which 12. Estenia C and B (Kuraray) composed of glass and alumina leads to better mechanical properties and wear resistance. ultrafine fillers Polymerization shrinkage decreases with a reduction in the resin 13. Gradia (GC Corp) has silica, silicate glass powder, and content. The inorganic filler content is 70–80% by weight and prepolymerized fillers.[1] 50–60% by volume, the resin content being lower, around 33%.[6] Artglass and Belleglass HP contain an excessive quantity of fillers, which makes them appropriate for the posterior teeth Polymerization Technique restorations. Solidex incorporates intermediate filler content, Additional extraoral light curing of IRC is not enough to increase which facilitates better esthetics for anterior teeth restoration. the rate of conversion. Hence IRCs require specific conditions The various second-generation IRCs available are, such as heat, pressure, vacuum, and oxygen-free environment for 1. Artglass launched in 1995 contains barium silicate glass filler. curing. The various techniques available for additional curing are It is photo-cured using a xenon stroboscopic light. Inlays, described below: Onlays, and crowns with/without metal substrate can be fabricated using this material Heat polymerization 2. Belleglass HP introduced in 1996 contains silanated microhybrid fillers. Surface and base composites, which are Ideally, the temperature applied in this technique must be above used on enamel and dentin, respectively. The smoothness the direct composite’s glass transition temperature (Tg). The [11] and polishability of the material are improved by the reduced temperature used for IRC ranges from 120 to 140°C. Within filler size[8] this temperature range, there is an increase in polymer chain 3. Sinfony launched by 3M ESPE contains fillers made of glass- mobility, favoring additional cross-linking and stress relief, but ceramic powders or ultra-fine glass. Uses Visio alpha and prolonged heating may cause degradation of the composite. Visio beta polymerizing units for polymerization[9] Source of heat can be applied by autoclaves, cast furnaces, 4. Targis launched in 1996 by Ivoclar Vivadent contains or special ovens. Amount of unreacted monomer level after trimodal filler of barium glass, spheroid silica and colloidal initial light curing is decreased during the post-cure heating of silica. It is cured using Targis power curing unit. Inlays/ resin composite. Primarily two mechanisms are involved in Onlays/veneers and anterior crowns can be fabricated and this phenomenon. First, due to heat treatment, the unreacted also used for veneering metal frameworks monomer bonds covalently to the polymer network, leading 5. SR Adoro (Ivoclar Vivadent) has dentin and enamel materials to an increase in conversion itself. Second, the heating process as the main component and also has a liner, stains, opaquer, causes volatilization of the residual monomers. Combination of and SR link (bonding agent). Targis system which has been both heat and light-curing increases the thermal energy to allow revised regularly and expressed now as SR Adoro better double-bond conversion. This combination of both heat 6. Solidex launched by Shofu which is an indirect ceramic and light-curing has increased the wear resistance by 35%, which polymer system and is light-cured using solidilite and sublite is in contrast to curing with light alone.[12]

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Nitrogen atmosphere additional cure and increased inorganic fillers that account to [1] Entrapment of oxygen in the resin restoration from surrounding 66% of total volume. Neves et al. concluded that the hardness air tends to inhibit the polymerization. This increases the wear value is directly dependent on the filler content. Materials with [15] rate by weakening the restoration wall around it. Removing increased filler volumes showed better mechanical properties. all of the encased air makes the restoration to become more Tanoue et al. reported that a combination of composite translucent. So before curing of the material begins, nitrogen material and curing unit from the same manufacturer provides pressure can be used to eliminate the internal oxygen, which the best mechanical and physical properties to the composite. influences the esthetics, DC, wear, and abrasion. This method of Yamaga et al. showed that heat might break the polymer double curing is utilized by BelleGlass and Sculpture Plus.[1] bonds into a single bond which facilitate monomer conversion, thus improves the polymerization of the unreacted monomers.[16] Slow or soft start curing Wear of composite material is influenced by the filler size, shape, volume, and bonding to matrix. Improved wear resistance The conception of slow curing given by Mehl showed that slower and enhanced physical and mechanical properties of IRC are due curing rate will allow greater level of polymerization. Faster or to the integration of multifunctional monomer, which allows rapid curing rate cause premature polymerization causing rigidity, control over the position along the carbon chain where the cross- stiffness, disallowing further propagation of the molecule. Both linking occurs. BelleGlass and Cristobal utilize the concept of soft-start curing.[13] Optical properties Electron beam irradiation Unpredictable color stability is the major problem with This is another method described for enhancing the properties composite material. The mode of curing and the remaining of the composites. It uses polymers such as polyethylene, double bonds are the factors which influence the color stability polysulfone, or polycarbonate. Two chief reactions such as chain of composites. For enhanced shade matching of IRCs, curing of breakage and chain linkage occur when a polymer is exposed to the uncured material on the tooth has to done with a hand-held electron beam irradiation. Induction of dense packing occurs curing unit, as some of these materials show net color change on at the region of chain breakage. This improves the mechanical curing.[17] properties and the success rate by influencing the bond between the matrix and filler. Polymer degradation and discoloration of the Marginal adaptation and microleakage resin are the main drawback of this method. The radiation dosage of 200 KGy is usually given. It is also shown that low dosage like Marginal adaptation is one factor that determines the longevity of 1 KGy also improves the properties of the composite.[14] the restoration. Aggarwal et al. reported that after thermocycling, indirect resin showed better bond strength and marginal Fiber reinforcement adaptation than direct restoration. Reduced polymerization contraction of IRCs gives better marginal adaptation than Smith in 1960 introduced fiber-reinforced composites. ceramics. Commonly used fibers in dentistry are glass and polyethylene. These fibers act as crack stoppers and enhance the properties of Surface properties composite. Fibers geometrical orientation is fixed and protected by the resin matrix. The surface roughness of the composite causes increased plaque When the applied force is perpendicular to the long axis of accumulation leading to the formation of secondary caries and the fibers, it will result in enhanced strength and when fibers failure of IRC restoration. The filler size and matrix monomer orient parallel to the forces, it will produce matrix-dominated influence the accumulation of biofilm. Biofilm adhesion can be failures. Multidirectional fibers show reduced strength in any reduced using fillers of smaller size with more weight percentage one direction when compared to unidirectional fibers.[1] and polishing with diamond paste to produces a smooth surface. High stress-bearing areas require materials with high elastic The surface roughness ranges from 6 to 8 µ. Presence of residual modulus, high flexural strength, high impact, low deformation, and uncured monomer also enhances the bacterial adherence. fatigue resistance. Composite resins flexural strength and modulus are influenced by the fiber volume, architecture, aging, and position. Surface treatments and its effect It is proved that enhanced mechanical properties are also achieved Adequate surface activation of the intaglio surface of IRC by the use of resin pre-impregnated silanized glass fibers. restoration through various surface treatments determines the adhesion of restoration to the tooth. Surface energy and Properties of Second-generation IRCs roughness of IRC are increased by airborne particle abrasion. These surface irregularities allow better retention of the luting Mechanical properties agent to the finished composite. Use of 1% hydrofluoric acid Enhanced mechanical properties with elastic modulus to 8.5– on IRC for 5 min causes dissolution of the inorganic particles 12 GPa and flexural strength of 120-160 MPa, is due tothe resulting in microstructural alteration of the composite. Surface

16 Journal of Advanced Clinical & Research Insights ● Vol. 8:1 ● Jan-Feb 2021 Indirect resin composite Agathian, et al. energy can also be enhanced by sandblasting with aluminum an alternative to ceramics in the fabrication of cement-retained oxide particles for 10 s. Application of silane after sandblasting FDP on implants.[20] improves the wettability of the treated surface, thereby increases the bond strength.[18] Conclusion

Fabrication of IRC Restoration Indirect composite systems provide an excellent alternative to tooth-colored posterior restorations. They can be an Direct-indirect/semi-indirect method excellent choice for patients when indicated. The success of In direct step, following application of separating medium, these restorations lies in proper diagnosis, planning, execution, the IRC material is condensed into the cavity. This separating and excellent laboratory support. Since there is no single ideal medium allows easy removal of the inlay after initial intraoral material which can be used for all restorative systems, it is up to curing. Following this, the restoration is removed and exposed to the operator to choose the appropriate restorative material and extraoral heat processing at 110°C for 7 min as an indirect step. technique according to the clinical situation. This method of fabrication eliminates the need of impression and is completed in single sitting. References

Indirect fabrication 1. Nandini S. Indirect resin composites. J Conserv Dent 2010;13:184-94. A die is fabricated for the prepared inlay cavity. After application 2. Price RB, Gerrow JD. Margin adaptation of indirect composite of separating medium to the die, incremental condensation of inlays fabricated on flexible dies. J Prosthet Dent 2000;83:306-13. composite material into the cavity is done. Light curing of each 3. Fahl N Jr, Ritter AV. Composite Veneers: The Direct-Indirect increment is done for 40 s. The light-cured inlay restoration is Technique. Chicago, IL: Quintessence Publishing Co.; 2020. then removed from the die and then subjected to heating an 4. Huth KC, Chen HY, Mehl A, Hickel R, Manhart J. Clinical study oven at 100°C for 15 min. Accurate proximal contour is achieved, of indirect composite resin inlays in posterior stress-bearing which makes this method advantageous.[1] cavities placed by dental students: Results after 4 years. J Dent 2011;39:478-88. 5. Poskus LT, Latempa AM, Chagas MA, da Silva EM, Leal MP, Clinical Application of IRC Guimarães JG. Influence of post-cure treatments on hardness and marginal adaptation of composite resin inlay restorations: Biofilm adhesion was found to be less in IRC than direct An in vitro study. J Appl Oral Sci 2009;17:617-22. composite resins. Failure of bond interface and polymerization 6. Mazumdar P, Das UK, Majumdar N. Degree of conversion of shrinkage leading to secondary caries is the major reason for indirect composite resin under Fourier transformation infrared the replacement of posterior composite restorations. Various spectroscopy-an in vitro study. Int J Adv Case Rep 2015;2:1410-7. techniques to overcome this problem are the use of glass ionomer 7. Gargari M, Ceruso FM, Pujia A, Prete V. Restoration of anterior bases, incremental method, and the indirect technique.[19] teeth using an indirect composite technique. Case report. Oral IRCs may reinforce the tooth structure and provides an Implantol (Rome) 2013;4:99-102. esthetic alternative for intracoronal restorations. The transfer of 8. Leinfelder KF. New developments in resin restorative systems. masticatory forces is considerably less in IRCs when compared J Am Dent Assoc 1997;128:573-81. 9. Kakaboura A, Rahiotis C, Zinelis S, Al-Dhamadi YA, Silikas N, to porcelain and porcelain-fused-metal restorations. When Watts DC. In vitro characterization of two lab-processed resin compared to porcelain, composites have the ability to absorb composites. Dent Mater 2003;19:93-8. the compressive and reduce the impact forces by 57%. Hence, a 10. Klymus ME, Shinkai RS, Mota EG, Oshima HM, Spohr AM, polymer of IRCs is considered while restoring the coronal aspect Burnett LH Jr. Influence of the mechanical properties of of a dental implant. composites for indirect dental restorations on pattern failure. Tsitrou et al. found that tendency for marginal chipping is Stomatologija 2007;9:56-60. lower in IRCs than ceramics. As the luting cement and composite 11. Eldiwany M, Powers JM, George LA. Mechanical properties of have similar composition, IRCs have better marginal adaptation direct and post-cured composites. Am J Dent 1993;6:222-4. than ceramics. IRC Onlays are an esthetic alternative to stainless 12. Bagis YH, Rueggeberg FA. The effect of post-cure heating on steel crowns for children. residual, unreacted monomer in a commercial resin composite. Tooth-colored IRCs are used as a veneering material to Dent Mater 2000;16:244-7. 13. Mehl A, Hickel R, Kunzelmann KH. Physical properties and gap acrylic denture teeth during fabrication of Rochette Bridges and formation of light-cured composites with and without softstart removable cast partial dentures and gingiva-colored composites polymerization. J Dent 1997;25:321-30. [20] are used for simulating the soft tissues for better esthetics. 14. Greer RW, Wilkes GL. Apparent reversal of physical aging by Nowadays, IRCs are used as a veneering material on to electron beam irradiation-furthur investigations. Polymer the titanium frameworks in replacement of acrylic due to its 1998;39:4205-10. advantageous mechanical properties during the construction of 15. Neves AD, Discacciati JA, Orefice RL, Jansen WC. Correlation Implant-supported hybrid prosthesis.[21] IRCs are also used as between degree of conversion, microhardness and inorganic

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content in composites. Braz Oral Res 2002;16:349-54. onlay with cavity sealing: A review of clinical procedures. 16. Yamaga T, Sato Y, Akagawa Y, Taira M, Wakasa K, Yamaki M. J Esthet Restor Dent 2014;26:97-106. Hardness and fracture toughness of four commercial visible 20. Pantzari AP. The use of indirect resin composites in clinical light-cured composite resin veneering materials. J Oral Rehabil practice: A case series. Dentistry 2013;3:1-6. 1995;22:857-63. 21. Lee EY, Jun SG, Wright RF, Park EJ. Comparative study of the 17. Lim SH, Lee YK. Changes in color and color coordinates shear bond strength of various veneering materials on grade II of an indirect resin composite during curing cycle. J Dent commercially pure titanium. J Adv Prosthodont 2015;7:69-75. 2008;36:337-42. 18. Soares CJ, Soares PV, Pereira JC, Fonesca RB. Surface treatment protocols in the cementation process of ceramic and laboratory How to cite this article: Agathian R, Manoharan PS, Rajkumar E. processed composite restorations. A literature review. J Esthet Indirect resin composite – A literature review. J Adv Clin Res Restor Dent 2005;17:224-35. 19. Alharbi A, Rocca GT, Dietschi D, Krejci I. Semidirect composite Insights 2021;8(1):13-18.

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