Written by Howard E. Strassler, DMD, FADM, FAGD, and Richard D. Trushkowsky, DDS, FAGD, FADM, FACD Wednesday, 31 December 2003 19:00
For many years, the restorative material of choice for direct placement of restorations in posterior teeth was dental amalgam. Although dental amalgam is the most used restorative material in the posterior region of the mouth and has proven to be remarkably durable,1 there has been a trend in recent years to restore posterior teeth with composite resin. The trend to use composite resin in the posterior region has been driven by the significant improvements in adhesion chemistry (specific to enamel and dentin) and the physical properties of composite resins.2
In the past, the choice of composite resin for posterior teeth was limited. Today, the introduction of improved composite resins with better physical properties and handling has led to a wider range of options for the practitioner regarding which type of composite resin to use to restore posterior teeth. The categories of composite resin to restore class 2 preparations in posterior teeth include hybrid, nanofill hybrid, high-density microfill, and high-viscosity (packable) composite resins (Table 1). These composite resins have demonstrated more in vitro wear resistance than previous small-particle composite resins.3-5 Clinical studies of the restoration of posterior teeth have shown that the current hybrid composite resins can be considered alternatives to amalgam in routine-sized preparations.6-11 The expectation is that the nanofilled hybrids will perform as well as or better than hybrid composite resins. While dental amalgam, cast gold, and porcelain/metal are still the standards for posterior tooth restorations because of their durability and ability to resist wear, for routine-sized preparations, composite resins can now be viewed as alternatives to metal restorations.12-13
An ideal composite resin for restoring posterior teeth should fulfill the following criteria15:
- Wear similar to natural tooth structure or dental amalgam.
- Does not display plastic deformation when in function.
- Requires a simple technique for placement.
- Demonstrates minimal shrinkage during polymerization.
- Displays excellent marginal adaptation and sealing.
- Possesses a radiopacity equal to or greater than enamel and dentin for ease of radiographic evaluation.
- Employs a quick, exact, nontooth destructive finishing technique.
- Is aesthetically pleasing in color and translucency.
Some of the difficulties associated with adhesive composite resins relate to shrinkage and gap formation during polymerization and their subsequent microleakage.16 Gap formation caused by resin shrinkage can contribute to loss of adhesion, bacterial invasion, recurrent caries, postoperative sensitivity, and pain on mastication.17 Polymerization shrinkage is one of the main factors that determines the longevity of composite resin restorations.18,19 When light-curing, placing the light closer to the gingival wall minimizes the thickness of the composite resin and can alleviate some of these problems.20
A successful posterior composite resin restoration is dependent upon a thorough evaluation of the patient’s occlusion and parafunctional habits. Placement of composite resins when a parafunctional habit such as bruxism exists can lead to greater wear of the composite as compared to a metal restoration. It is important to also remember that for patients with parafunctional habits, ceramic restorations will cause significant wear of opposing tooth structure and other restorative materials, including composite resin and metallic restorations. The rate of wear for posterior composite resin restorations is dependent on tooth position in the arch and the size of the preparation.26 Supporting cusps that are replaced with composite resin will demonstrate more wear than nonsupporting cusps. The rate of wear increases as the preparation width at the isthmus increases beyond one third of the intercusp distance.7 Even with these considerations, the literature supports the use of composite resin as an equivalent to amalgam in moderately sized class 1 and class 2 preparations.12
Some general guidelines to improve clinical success with posterior composite resins include the following:
- Preparations in which an occlusal contact is supported by tooth structure.
- Supragingival margins and the ability to place a dental dam.
- Enamel margins are preferred. However, margins on cementum are acceptable if the margin is supragingival after dam placement.
In cases where initial caries is only on the proximal surface, a conservative slot preparation of the proximal surface combined with a sealant for the occlusal surface will suffice. When the caries extends into the occlusal pits and fissures or if an existing class 2 amalgam or composite resin is being replaced, an isthmus width of one fourth to one third the intercusp distance is preferred to minimize wear of the composite resin in function.
ACHIEVING PREDICTABLE PROXIMAL CONTACTS
A frequent problem with class 2 composite resin restorations has been achieving predictable, anatomic proximal contacts.15,27 This problem directly relates to the fact that composite resins are viscous materials that cannot be condensed and pushed against matrix bands in a predictable manner. Even the most viscous packable composite resins are liquids that are not dense enough to move a matrix band in order to achieve proximal contact and adaptation via slight movement of the teeth during the placement process.28 Although the use of a wedge before tooth preparation can help compensate for the thickness of the matrix band,15 modifications in matrix design, type of metal used, thickness, and retainer systems have been introduced to eliminate the problem of poor proximal contacts with composite resin restorations.
A patient presented with clinical and radiographic evidence of caries on the mesial and occlusal surfaces of the mandibular second molar and caries on the distal and occlusal surfaces of the mandibular first molar (Figure 1). The patient had a history of latex sensitivity, so a latex-free dental dam (Flexi-Dam [Coltene-Whaledent]) was used for the restorative procedure. The teeth were prepared with a 245 bur (SS White Burs). The preparation design had cavity walls that were convergent or parallel from the pulpal wall. The occlusal cavosurface margins were at right angles to the cusp ridges. This right angle margin allows for a bulk of composite resin at the high-stress-bearing occlusal margin that will prevent fracture of the composite resin. Also, beveling the gingival margin of a class 2 composite resin preparation should be avoided, even if it ends on enamel. Usually, a limited amount of enamel remains at the cervical margin, so beveling this margin removes the remaining enamel, which compromises adhesion.32
Figure 1. Preoperative view of the mandibular first and second molar.
Figure 2. Class 2 preparations on the mandibular first and second molars.
Figure 3. Placement of a resin-reinforced glass ionomer liner on the pulpal and axial walls of the cavity preparations.
Figure 4. Light-curing the glass ionomer liner with an LED light.
Figure 5. The cavity preparations with glass ionomer liners.
Figure 6. Phosphoric acid etchant applied to tooth preparations.
After tooth preparation (Figure 2), a periodontal probe was used to determine the depth of the proximal boxes from the gingival margin to the marginal ridge. For each proximal box, a disposable Trimax tip was adjusted so that the marginal ridge would be lined up with the instrument when light-curing the composite resin. This occurs after liner placement.
|Figure 7. After rinsing the etchant from the tooth, a single-bottle adhesive was applied.||Figure 8. Placement of 2 sectional matrices (ComposiTight with G-Ring, Garrison Dental Solutions) for a MOD preparation.|
|Figure 9. Supporting a sectional matrix with a bite registration paste without a separating matrix ring.|
When restoring the proximal contact, a thinned, stainless steel matrix band allows shaping to achieve a positive, anatomic proximal contact. Although a sectional matrix was not used for this case, a sectional matrix with a retainer ring can be used to restore proximal surfaces of posterior teeth (Figure 8). In some cases, the retainer ring cannot be used because of anatomic variation in width of some posterior teeth. In these circumstances, a sectional matrix stabilized by a wedge can be placed, and the matrix can be supported with bite registration material (Figure 9). Since the preparations were adjacent to each other and there was difficulty placing a sectional matrix with a retainer ring, it was decided to first use a conventional matrix band to restore the mesio-occlusal segment of the second molar. The second molar with the dam clamp in place precluded the use of a matrix retainer, so the matrix was adapted to the tooth for restoration without a retainer.
|Figure 10. The Gradia Direct preloaded tubes were warmed in a Calset unit (AdDent).||Figure 11. The use of the Trimax (AdDent) tip to enhance light-curing in the proximal box.|
The nanofilled hybrid composite resin chosen for the restoration (Gradia Direct [GC America]) was heated with a Calset unit. Once heated, the composite resin was inserted into the proximal box of the cavity preparation, filling it to the axiopulpal line angle. The Trimax tip was placed into the composite resin, slowly pushing the tip toward the adjacent tooth. The curing light guide was placed, touching the top of the Trimax tip at right angles, and the composite resin was cured for 10 seconds (Figure 11). The space left by the Trimax tip was then backfilled to the height of the proximal box and light-cured.
|Figure 12. The preparation was filled with composite resin in increments and light-cured. The final increment was shaped with a hand instrument wetted with adhesive resin.||Figure 13. The margin of the restoration was finished with an egg-shaped finishing bur.|
|Figure 14. Initial polishing was accomplished with an aluminum oxide-impregnated rubber abrasive point (Astropol, Ivoclar/Vivadent).||Figure 15. Final polish with a diamond polishing paste and a prophylaxis brush.|
|Figure 16. The restoration of the mandibular first and second molars is completed.|
The dental dam was removed, and the slight excess of composite resin at the occlusal margins was finished using an egg-shaped finishing bur (Brasseler, Figure 13). Further definition of the anatomic form was accomplished with an aluminum oxide-impregnated rubber polishing point (Astropol [Ivoclar/Vivadent], Figure 14). The most difficult margin to access of any posterior class 2 restoration is the gingival interproximal margin. Finishing strips do not work well on rounded or concave root and interproximal surfaces. Likewise, rotary handpieces with rotating diamonds and burs are contraindicated for interproximal surfaces in cases such as this because they can create unnatural embrasures and notched and irregular surfaces. This margin can be best managed and finished using a Profin reciprocating handpiece with a Lamineer tip (Dentatus). The flat, safe-sided abrasive Lamineer tip allows for precise and controlled finishing and polishing of the cervical interproximal margin. An alternative instrument that can be used to remove excess resin in these areas is a 12A scalpel blade.
The concepts and techniques described in this article can be used to provide patients with durable and aesthetic posterior composite resin restorations. To ensure an anatomic proximal contact, pre-wedging, specialized matrices, and modifications to the curing phase of treatment will eliminate the problems previously encountered when restoring proximal surfaces with composite resin. Postoperative sensitivity associated with posterior composite resins can be minimized by using bondable resin or glass ionomer liners for cavity preparations of moderate depth. The problems associated with gap formation at the gingival margin due to polymerization shrinkage of the composite can be minimized by using a Trimax light curing tip.
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