As patients seek aesthetic treatment that is biocompatible, durable, and safe, the utilization of composite resin for the direct restoration of the posterior dentition has continued to increase. In the past, composite resins were often affected by factors (eg, low wear resistance, color variation, low flexural strength) that limited their use to smaller restorations. Newer formulations, however, have significantly enhanced the physical, mechanical, and optical properties that have increased their use in medium to larger restorations.
Consideration Factors for Utilization of Direct Composite
The integrity of the bond and the marginal adaptation to the tooth structure are critical for clinical success in posterior composite restorations.1 Optimizing the adhesion of restorative biomaterials to the mineralized hard tissues of the tooth is a decisive factor for enhancing their seal, mechanical strength, and marginal adaptation. The search for a tooth-restorative interface that mimics the natural tooth condition has resulted in the establishment of an effective micromechanical bond between composite and mineralized tooth structure. These advances in adhesive biomaterials have resulted in restorations that provide increased retention, marginal adaptation and seal, and reduced microleakage. This evolution has dramatically changed the limitations of direct composite restorations.
In a procedure using composite resins, the polymerization reaction of the resin-matrix phase can compromise dimensional stability.2 This conversion of the monomer molecules into a polymer network is accompanied by a closer packing of the molecules, leading to bulk contraction.3 Alternatively, when a curing material is bonded on all sides to rigid structures, bulk contraction cannot occur and shrinkage must be compensated for by increased stress, flexure, or gap formation at the adhesive interface.2 The shrinkage stresses are transferred to the surrounding tooth structure, since it restricts the volumetric changes.3 Some factors that influence shrinkage include: type of resin, filler content of the composite,3 curing characteristics,4 cavity configuration,5 and the light intensity used to polymerize the composite.6
Although polymerization is the cause, shrinkage stress may be the mechanism behind challenges (eg, microleakage, postoperative sensitivity, staining, caries, pulpal irritation) commonly encountered with adhesive restorations.2,7 To overcome these challenges, several methods for stress reduction can be considered when the clinician is selecting materials that are subject to shrinkage. These methods include reducing the light intensity of the curing unit,6 incrementally placing small layers of composite resins, and selecting low-shrinkage composite systems. 8
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Anatomy and Occlusion
In the past, practitioners often had difficulty achieving precise marginal integrity, ideal proximal contacts, and anatomical contours for larger cavity preparations. Advances in proximal contouring devices (ie, sectional matrices) and improved sculptability of contemporary resin materials have complemented incremental layering techniques (eg, horizontal, vertical, oblique) and light-curing methods (ie, three-sited, light-curing method). This has resulted in improved proximal contact, elimination of overhangs, ideal tooth contours, minimizing or eliminating excess resin at the proximal line angles, improved marginal integrity, and a reduction in microleakage at the gingival margin.
In addition, the clinician may also be able to determine the following from the preoperative environment: anatomic morphological details (eg, developmental grooves and the shape of embrasures, prominences, convexities), or any other characteristic that can prove helpful when reconstructing tooth surfaces.A hand-drawn, occlusal diagram can also be made prior to the administration of anesthesia and rubber dam isolation, which allows preoperative occlusal stops, wear facets, and excursive guiding planes to be recorded with articulation paper. Initial occlusal registration is valuable for preparation design when considering placement of centric stops beyond or within the confines of the restoration, and in minimizing occlusal adjustments and finishing procedures.9
Cavity Preparation and Dimension
Tooth preparation for direct composite restorations differs from preparation for laboratory-processed inlays. Preparation design is based on one’s knowledge of and experience with the physical and mechanical properties of these new restorative materials. Since resistance and retention are determined primarily by adhesion to enamel and dentin, a more conservative preparation is achievable.10 A conservative preparation design can be utilized because the adhesive procedure strengthens the cusps and provides additional support; this preserves sound tooth structureand requires no extension for prevention. The preparation is limited to access of the defect, removal of existing caries and pre-existing restoration, and requires less volume to resist clinical fracture than a metallic restoration (ie, amalgam) or laboratory-processed inlay. The cavity dimension for medium to larger occlusal and approximal cavity preparations can be more conservative for direct composite restorations than inlays because the preparation does not require the removal of undercuts for a proper path of insertion and adaptation to the cavity walls. In addition, the direct-placement method can be used with minimal preparation because it uses the undercuts and surface irregularities to increase the surface area for bonding. This conservation of dentin and reinforcement of tooth structure using composite resin reduces the possibilities of fracturing during function or in the event of traumatic injury (Figures 1-2-3).
From the wide range of restorative biomaterials, direct composite resin systems provide an aesthetic alternative for intracoronal posterior restorations. The clinical attributes include: completion in a single visit, no impression or provisional restoration required. The operator has total control of the restorative process and the surrounding dentition for comparison. Utilization of direct composite resins with the aforementioned consideration factors should be employed to complimentthe existing clinical repertoire. Part II of this discussion will address the consideration factors for the use of laboratory-processed composite and porcelain intracoronal restorations as well as provide a comparison of the attributes and capabilities of each system.
*Assistant Professor, Department of Restorative Dentistry and Biomaterials, University of Texas Health Science Center Dental Branch, Houston, TX; private practice, Houston, TX.
- Bouschlicher MR, Cobb DS, Boyer DB. Radiopacity of compomers, flowable and conventional resin composites for posterior restorations. Oper Dent 1999;24(1):20-25.
- Davidson CL, Feilzer AJ. Polymerization shrinkage and polymerization shrinkage stress in polymer-based restoratives. J Dent 1997;25(6):435-440.
- Venhoven BA, de Gee AJ, Davidson CL. Polymerization contraction and conversion of light-curing bisGMA-based methacrylateresins. Biomaterials 1993;14(11):871-875.
- Quellet D. Considerations and techniques for multiple bulk-fill direct posterior composites. Compend Contin Educ Dent 1995;16(12):1212,1214-1216.
- Feilzer AJ, de Gee AJ, Davidson CL. Setting stress in composite resin in relation to configuration of the restoration. J Dent Res 1987;66(11):1636-1639.
- Feilzer AJ, Dooren LH, de Gee AJ, Davidson CL. Influence of light intensity on polymerization shrinkage and integrity of restoration-cavity interface. Eur J Oral Sci 1995;103(5):322-326.
- Bausch JR, de Lange K, Davidson CL, et al. Clinical significance of polymerization shrinkage of composite resins. J Prosthet Dent 1982;48(1):59-67.
- Asmussen E. Composite restorative resins. Composition versus wall-to-wall polymerization contraction. Acta Odontol Scand 1975;33(97):337-343.
- Liebenberg WH. Successive cusp build-up: An improved placement technique for posterior direct resin restorations. J Can Dent Assoc 1996;62(6):501-507.
- Robbins JW, Fasbinder DJ, Burgess JO. Posterior inlays and onlays. In: Fundamentals of Operative Dentistry: A Contemporary Approach, Carol Stream, IL: Quintessence Publishing; 1996:229-249.