Achieving Form and Function for Class II Restorations: A Simplified Technique

With the increased demand for natural-looking restorations, direct resin bonding is performed to conservatively and aesthetically restore posterior teeth. In the past our restorative options included, but were not limited to, gold, amalgam, or first-generation composites. Today’s resin formulations have advanced to where they have durability as well as many other critical features that ensure optimal aesthetics in addition to form and function.¹ The improved wear resistance of these composites has contributed to their success in the intraoral environment. Accurate proximal contacts can be achieved when these materials are delivered with the appropriate clinical protocol and instrumentation.² Segmental matrix bands provide ease of positioning, the ability to restore multiple proximal restorations in a given quadrant, and ideal 3-dimensional contour. These bands are generally used with contact rings that apply pressure interproximally to ensure adequate proximal contacts (eg, ComposiTight [Garrison Dental Solutions]).
Polymerization shrinkage has remained a clinical challenge for direct resin restorations.³ Creating rounded internal line angles minimizes shrinkage stress and the resulting deleterious effects.^4,5 Appropriate rotary selection is fundamental for successful cavity preparation design. The loss of adhesion from cavity walls or the fracture of enamel prisms at the cavosurface margins can be attributed to polymerization shrinkage. Shrinkage stress can have a detrimental effect on the dental adhesive used, as bond strengths immediately postcure and after 24 hours are substantially different.⁶ The most noticeable clinical effects are postoperative pain upon chewing and extreme temperature sensitivity. This extreme discomfort is unpleasant for the patient and requires the entire restorative procedure to be redone. Factors that are out of the dentist’s control are the various light activation/application techniques. These alternate curing modes, in an attempt to enhance the rate of polymerization to minimize shrinkage stresses,^7-9,10,11 have not shown significant advantages. There are various opinions as to whether the degree of conversion is compromised when resins are photo-activated using these novel techniques.¹²
The longevity of composite resins continues to improve as a result of their composition. The physical, tactile, and aesthetic properties of current resin systems enable the clinician to deliver restorations that closely mimic natural dentition. The inherent characterizations of the teeth can be replicated through the use of predictable stratification techniques.⁵
Today’s microhybrid resins (eg, Venus [Heraeus Kulzer], Premise [Kerr/Sybron Dental Specialties], or Filtek Supreme Plus [3M ESPE]) have been developed in response to the increasing demand for more durable and aesthetic restorations. Microhybrid composites are suitable for most direct anterior and posterior restorations, effectively simulating natural fluorescence, opalescence, translucency, and light refraction.
The following clinical presentation outlines a step-by-step procedure for achieving optimal aesthetics and proximal contact form in a class II restoration using a microhybrid resin (Venus, Venus Flow [Heraeus Kulzer]) in a direct resin buildup.

CLINICAL PROTOCOL

Patient Presentation and Consultation

Figure 1. Preoperative occlusal view of the maxillary right first premolar. Note failing composite with recurrent decay. The adjacent restoration on tooth No. 4 is still functioning.

The initial step in the restorative protocol is the comprehensive clinical examination performed to determine an accurate diagnosis for the patient’s existing clinical condition. In this case, a 35-year-old patient presented with pain in the maxillary right posterior region. Radiographic and clinical examinations determined that the existing resin restoration on tooth No. 5 (upper right first premolar) had recurrent decay and marginal breakdown present (Figure 1). Various treatment options were reviewed with the patient to ensure an understanding of the existing clinical condition, and in this case a direct class II restoration was the most ideal treatment to restore the dentition to proper health, function, and aesthetics.

Preparation Design and Resin Buildup

Figure 2. A rubber dam is placed to achieve tooth isolation and to ensure proper control of moisture in the operative field.

Figure 5. Preparation continues with a friction grip carbide No. H245-008.	Figure 6. Preparation is complete. Rounded internal line angles prevent voids from forming during composite placement.

Prior to placement of a rubber dam, it was necessary to select the shade. This facilitated an accurate final shade that could otherwise be compromised by desiccation. The patient was then anesthetized, and the rubber dam was placed to ensure proper moisture control in the operative field (Figure 2). To achieve an optimal gingival seal for the rubber dam opening at the tissue interface, a flowable resin (eg, Venus Flow, Premise Flow, or Filtek Supreme Plus Flow) may be applied at this time.
Tooth preparation was initiated with the new No. H31-010 carbide bur (Komet USA; Figure 3) to remove the existing resin restoration (Figure 4). The innovative, geometric design of this carbide allows for fast, smooth, and effortless removal of the material. With virtually no vibration or chatter, iatrogenic craze lines are minimized. A caries-indicating solution was then applied to the tooth surface to ensure that all carious tooth structure was removed.¹³ Preparation continued with a friction grip carbide No. H245-008 (Figure 5). Retentive grooves are unnecessary for contemporary adhesive restorations, as bond strengths facilitate predictable retention when applied to ideally prepared and conditioned tooth surfaces.⁵ Rounded internal line angles were created to prevent voids from forming during composite placement (Figure 6). In anticipation of the placement of a sectional matrix band, it is important for the clinician to ensure that contact with the adjacent tooth is broken. To help eliminate unsupported enamel, a narrow, serrated, medium grit polishing strip was used.

Figure 7. Occlusal view of the premolar site following the application of sectional matrix, wedge, and retaining ring.	Figure 8. The dentin bonding agent is applied in 3 successive coats and then gently air-dried.

To facilitate adaptation of the microhybrid composite, a contoured sectional matrix band was placed (Composi-Tight), securing it with a wedge at the gingival margin. The wedge would seal the matrix at the gingival margin yet allow the contours of the matrix to establish ideal contact with the adjacent tooth. Using a blunt instrument, proximal contact was verified by burnishing the matrix; it should not move when sufficient contact exists (Figure 7).
Once retaining rings were inserted and the curved matrix approximated the ideal contacts, the adhesive procedure was initiated. Traditionally, the total-etch technique (ie, the application of phosphoric acid to the enamel and dentin for 15 and 10 seconds, respectively) is used to prepare the tooth for bonding^14-16 (Figure 8). The tooth was then rinsed (a wetting agent can be applied to rehydrate the tooth if desired).¹⁷ When the collagen bundles within the dentin collapse after the tooth is etched and dried, a rewetting agent must be applied to open the dentin tubules and ensure a better saturation of the resin primer into the collagen bundles, resulting in a secure bond strength.¹⁸ At the clinician’s discretion, self-etching materials and procedures can also be used as alternatives to the total-etch technique.¹⁹

Figure 9. Following the application and air-drying of the dental adhesive, it is light-cured.	Figure 10. A thin layer of flowable composite is placed in the gingival box in increments of no more than 1 mm in thickness to prevent any polymerization shrinkage.

Following the total-etch procedure, 3 or more successive layers of adhesive (Gluma Comfort Bond and Desensitizer [Heraeus Kulzer]) were applied, air-thinned for approximately 5 seconds, and light-cured for 20 seconds (Figure 9). Depending on the depth of the cavity, the clinician may opt to place a flowable resin on the entire cavosurface floor as a means to eliminate deep surface irregularities that make it difficult to achieve ideal adaptation of the composite body. This procedure helps to minimize polymerization shrinkage and eliminate voids around the internal line angles of the cavity preparation. The flowable resin is cured for 20 seconds.
A thin layer of flowable composite was also placed in the gingival box, not to exceed 1 mm in thickness. This thickness minimizes the chance of polymerization shrinkage, thus decreasing the chance for an open margin. Open margins at the gingival box level have been the main source of class II failures (Figure 10).

Figure 11. The initial layer of microhybrid composite resin is placed along the mesio-buccal line angle.	Figure 12. The layering process is continued sequentially until the tooth is restored to its original anatomical contour and form.

The first increment of microhybrid resin was placed in a layer approximately 2 mm in thickness along the mesio-buccal line angle. Increments of less than 2 mm result in a one-dimensional cure. As the material is shaped and contoured against the proximal walls and matrix, care must be taken to precisely adapt it to the marginal finish line (Figure 11). This increment of composite, and subsequent layers, were cured for 20 seconds. The layering process was continued sequentially until the tooth was restored to its original anatomical contour and form (Figure 12).

Figure 13. A final layer of flowable composite is placed over the entire restored surface.

After all increments are placed the clinician has the option of placing a final layer of flowable composite over the entire restored surface. This layer will help minimize any microgaps that may have developed during resin stratification (Figure 13). When cured, this will provide a more durable tooth/restorative material interface.^20,21 Should the patient request natural tooth characterizations, pit and fissure staining can be performed to achieve the desired effects.

Figure 16. Occlusion is verified with articulating paper.	Figure 17. The restoration is polished with a succession of carbide burs.

Figure 18. The final restoration is anatomically correct and has a natural luster.

Using forceps or Howe pliers, the retaining ring, wedges, matrix band, and rubber dam were removed. Preliminary anatomical contouring of the restoration was performed with a series of diamond finishing burs. Tertiary anatomy was incorporated with the use of a fine-grit Micro Prep diamond No. 8889M-007 (Komet USA; Figure 14). This instrument provides the clinician with better control in creating anatomically correct pits and fissures (Figure 15). The final restoration was digitally x-rayed to ensure the absence of overhangs. The occlusion was verified with articulating paper (Figure 16). The restoration received a final polish with a succession of carbide burs beginning with a No. 7801 (No. H247-009, Komet USA; Figure 17) to create a natural luster that satisfied both patient and clinician. The final view of the completed restoration shows a restoration that has restored both form and function (Figure 18).

CONCLUSION

When performing direct resin procedures, the clinician should recognize that each technique is sensitive in its own right. To provide the patient with an attractive, long-term, stable result, it is essential to understand the various direct resin protocols and materials involved. Once these are mastered, such cases become a series of easy, predictable steps that can be repeated as necessary. A functional, aesthetic result is the goal for all restorative procedures. By learning the necessary regimens, clinicians can gain a comfort level for restoring all classes of defects.

References

Dr. Shannon is a 1987 graduate of Dalhousie University School of Dentistry, Halifax, Nova Scotia. He lectures throughout North America, Australia, Asia, and Russia on mastering aesthetic restorative dentistry. He sits on a number of peer-reviewed editorial boards and has been a part-time clinical instructor at a number of post-graduate clinical programs in the area of aesthetic restorative dentistry. Dr. Shannon maintains a private practice with a focus on comprehensive aesthetic restorative dentistry in Vancouver, British Columbia, Canada. He can be reached at (604) 669-6700 or at info@dr-shannon.com.