Predictable Restoration of Class 2 Preparations With Composite Resin

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


The American Dental Association Council on Scientific Affairs stated that composite resin restorations allow for more conservative preparations, thereby preserving tooth structure. The guidelines also state that resin-based composites can be used for pit and fissure sealing, preventive resin restorations, initial class 1 and class 2 lesions using modified cavity preparation design, and for moderate-sized class 1 and class 2 restorations. The consensus of the council was not to use composites when teeth demonstrate heavy occlusal stress, when the preparation cannot be isolated, or for patients who are allergic or sensitive to resin-based composites.12 The advantage of current composite resins over dental amalgam is that they are highly aesthetic, they serve to reinforce tooth structure, and their preparations conserve more tooth structure.14

An ideal composite resin for restoring posterior teeth should fulfill the following criteria15:

  1. Wear similar to natural tooth structure or dental amalgam.
  2. Does not display plastic deformation when in function.
  3. Requires a simple technique for placement.
  4. Demonstrates minimal shrinkage during polymerization.
  5. Displays excellent marginal adaptation and sealing.
  6. Possesses a radiopacity equal to or greater than enamel and dentin for ease of radiographic evaluation.
  7. Employs a quick, exact, nontooth destructive finishing technique.
  8. 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 major challenge with any composite resin restoration is the need for excellent isolation (usually including a dental dam) to ensure an operative field that is not contaminated during adhesion. In most cases, the adhesive technique is multistep, and the area must be isolated from saliva and blood. What also must be taken into account is the time needed for the incremental placement of composite resin, which will minimize polymerization shrinkage. This is especially important in the area of the gingival margin. Using a total-etch technique with phosphoric acid, the clinician must be aware of isolation, the specific steps of adhesive placement, the additional step of rewetting dentin for optimal bonding, and the application of the dentin primer and adhesive resin.21-23 

Currently, the acceptable techniques for composite resin adhesion in class 1 and class 2 cavity preparations are a total-etch multiple-bottle adhesive system, a total- etch single-bottle adhesive system, a self-etch 2-step adhesive system, and a self-etch single-step adhesive system.6-8,15,24,25

TREATMENT PLANNING
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:

  1. Preparations in which an occlusal contact is supported by tooth structure.
  2. Supragingival margins and the ability to place a dental dam.
  3. 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.


Although longevity of composite resin restorations improves with conservative preparations, there are times when other clinical situations dictate the use of a composite resin restoration. For example, if a tooth-colored restorative material is desired by the patient, a direct composite resin or an indirect composite resin inlay/onlay may be placed. Contraindications to the use of composite resin as a directly placed posterior restorative include (1) the inability to place a dental dam or adequately isolate the area during placement of the restoration, and (2) patients who are allergic or sensitive to resin-based composites. Posterior teeth exhibiting moderate to severe wear due to attrition or parafunction habits are not good candidates for posterior composite resins. Research has shown that larger than recommended tooth preparations, especially in second molars, will not be as durable as smaller preparations in the same teeth. In these cases, laboratory-fabricated restorations are a better alternative, especially when cusps are being replaced.26

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.


The most commonly used approach for obtaining proper proximal contacts has been the application of thinner, dead-soft stainless steel matrix bands. These bands are available for use in a Tofflemire-type matrix retainer, eg, the HO band (Young Dental), a 0.001-inch dead-soft stainless steel band; Microbands (Dental Innovations), a conventional Tofflemire-type matrix band that has been machined to be ultrathin in the contact area; or as a circumferential retainerless matrix, eg, Automatrix (DENTSPLY/Caulk) or Supermat (Kerr/Hawe). These circumferential-type matrix systems are ideal for use with class 2 MOD preparations. For 2-surface class 2 preparations restoring only a single proximal surface, a sectional matrix system is appropriate. Examples include the Palodent matrix with a BiTine Ring (DENTSPLY Caulk); Contact Matrix (Danville); and the ComposiTight matrix with G-Ring (Garrison Dental Solutions). The last system utilizes an ultrathin dead-soft stainless steel sectional matrix in combination with a ring that when placed achieves some additional tooth separation.

Besides thin matrix bands, other devices have been introduced to assist in achieving an anatomic proximal contact with class 2 composite resins. Some of these devices (eg, contact formers [American Eagle Instru-ments] and Contact Pro [CEJ Dental]), allow the clinician to push against the matrix band while light-curing. While these devices can achieve the desired result, they are limited in that they do not fit all preparations. Other devices include the Light-Tip (Denbur) and ProxiCure tips (Ultradent), which are fitted over the curing light tip and can be inserted into the proximal box of the cavity preparation, allowing light penetration into the critical gingival area of the tooth preparation.29 However, because of the design of the tip, it will not form the contact predictably in the correct anatomic location, and in some instances its size precludes use in more conservative cavity preparations. 

Recently a smaller, more anatomically shaped tip (Trimax [AdDent]) was introduced to enhance light dispersion into all aspects of the proximal box, while at the same time allowing for pressure on the matrix band to achieve a positive anatomic proximal contact. It is easy to control, and if necessary, it can be modified for minor variations in preparation size and shape. It is a single- use disposable tip, so problems associated with a decrease in light penetration through the tip due to repeated autoclaving do not occur. Another benefit of using a light-conducting device such as the Trimax is that there will be a reduction in the amount of composite resin being cured in the proximal box at the gingival margin, thereby reducing the polymerization shrinkage gaps that can occur.26,27 The light-transmitting device directs the curing light to the depths of the composite resin in the proximal box.

CASE REPORT
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.


In recent years, the guidelines for using bases, liners, and sealers have changed as the materials have changed.33 If the preparation is of moderate depth, a glass ionomer or a resin liner such as a flowable composite is recommended. These liners have been shown to decrease postoperative sensitivity in posterior teeth restored with composite resins.34,35 In this case, because of the moderate depth for both cavity preparations, it was decided to use a light-cure, resin-reinforced glass ionomer liner on the internal dentin walls of the cavity preparation adjacent to the pulp. After tooth preparations were completed and cleansed, a light-cure, resin-reinforced glass ionomer liner (Fuji Lining LC [GC America]) was placed on the axial and pulpal walls of the preparations (Figure 3). The Fuji Lining LC was light-cured with a high-intensity LED curing light (Allegro [Den-Mat]) for 10 seconds (Figure 4). Figure 5 demonstrates placement of the Fuji Lining LC on the cavity walls. 

It was decided that a total-etch adhesive procedure would be used for the restoration. Currently, evidence supports the routine use of total-etch techniques for restoring posterior teeth.25 The teeth were etched for 15 seconds with a 32% phosphoric acid etchant (UltraEtch [Ultradent]) (Figure 6), then rinsed and dried. This left any exposed dentin with a glossy appearance, indicating that it was slightly moist. The single-bottle primer/adhesive (UniFil Bond [GC America]) was applied to all the internal walls of the cavity preparation, and a gentle air stream was used to evaporate solvent and thin the adhesive (Figure 7). Using a Trimax tip in each proximal box, the adhesive was light-cured for 10 seconds with the Allegro LED light. The occlusal portion of each preparation was also light-cured for 10 seconds. 

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.


The newer generation of nanofilled composite resins are more viscuous than other hybrid composite resins.36,37 Adaptation of high-viscosity composite resins in cavity preparations can be a problem.38-40 To overcome this problem, a device to heat the preloaded tip of composite resin was introduced (Calset [AdDent]). The Calset device heats the composite resin to 130°F (Figure 10). The thermal change in the composite resin makes it flow more easily into the cavity preparation, resulting in improved adaptation. It has been shown that heating the composite has no adverse effects on the physical properties and it can shorten curing time.41,42 

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.


The remaining cavity preparation was filled in 2-mm depth increments and shaped with hand instruments (Figure 12) and light-cured. With the matrix removed, the proximal surface was shaped with a long, needle-shaped finishing bur (ET 9 [Brasseler]), followed by shaping, finishing and polishing with thin finishing disks (Soflex XT disks [3M-ESPE]). The matrix was then placed on the first molar. With the proximal surface of the restoration on the second molar contoured and polished, the disto-oclusal segment of the first molar was restored following the procedure described, except an ultrathin (at contact area) matrix band (Microbands [Dental Innovations]) in a Tofflemire-type retainer was employed. 

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 occlusion was checked and adjusted. The final polish was accomplished using a diamond polishing paste with a brush (Figure 15). The final restorations demonstrate excellent anatomic form (Figure 16).

CONCLUSION
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.


With the current evidence, it is expected that these nanofill hybrid composite resin restorations will perform as well as conventional hybrid composite resins that have been in use for more than 15 years.


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