Direct Composite Restorations in the Posterior Region

The natural structure of a tooth is polychromatic and can possess a vast combination of colors, translucencies, and opacities that must first be perceived by the eye and then interpreted by the brain. To achieve an esthetic result, clinicians select and layer composite resin in a way that most closely simulates the inherent characteristics of the tooth. This concept of visualizing the color of tooth structure and then selecting a composite resin or resins that most closely mimic it is called chemical color selection. Color interpretation results from a combination of the three principles of tooth color: hue, value, and chroma. Hue is defined as the color that is perceived by the clinician (eg, red, blue, grey), value is the lightness or darkness of the hue, and chroma relates to the saturation or degree of intensity of color.¹ Commercially available shade-selection devices utilize these concepts to aid the clinician in selecting an appropriate tooth shade, and dental manufacturers create direct restorative materials to closely mimic the standard shade guides. However, when comparing a standardized shade tab with tabs fabricated from various restorative materials, subtle variations can be observed, which can reduce the predictability of the color expected by the clinician.²

Another concept by which color can be visualized is structural color. Natural teeth and restorative materials contain microscopic structures that interfere with certain wavelengths of light. Structural color plays a role in color reflection and opalescence in some animal species, including in butterfly wings and peacock feathers.³

This technology was recently introduced into composite resin direct restorative materials. The reality of color matching is that teeth possess a limited range of colors (ie, red to yellow) with varying degrees of lightness, darkness, and saturation. If a composite resin can utilize the physical properties of light (ie, diffraction, refraction, interference, scattering) to generate a red-to-yellow color that will match adjacent tooth structure (Figure 1 and Figure 2), esthetic results can potentially be achieved using only one composite in most clinical scenarios.

A patient presented to the office with caries on teeth Nos. 4 and 5 (Figure 3). Direct bonding was recommended for a mesial-occlusal-distal (MOD) restoration on tooth No. 4 and a distal-occlusal (DO) restoration on tooth No. 5, and the patient consented to treatment. Following complete removal of the caries, a single-shade composite resin with structural color-matching properties (OMNICHROMA, Tokuyama Dental America) was placed incrementally into the preparation. This composite has physical characteristics that are comparable to strong posterior composites as well as spherical fillers that promote the opalescence and polishability needed for anterior composite restorations. After the occlusal and interproximal contacts were verified, the restorations were polished (Figure 4).

This patient presented with a failing amalgam restoration on tooth No. 2 that was accompanied by caries on the mesial and distal surfaces (Figure 5). Treatment options were discussed, and it was mutually decided to restore this tooth with a direct-bonded restoration. The amalgam restoration was removed, and the preparation was extended to include the mesial and distal surfaces. When the restoration and secondary caries were removed, the tooth structure on the pulpal floor was revealed to be discolored from the amalgam. To prevent shade-matching interference, a supplemental composite material (OMNICHROMA BLOCKER, Tokuyama Dental America) was placed on the pulpal floor of the occlusal aspect of the preparation first, and then composite resin (OMNICHROMA, Tokuyama Dental America) was placed in 2-mm increments until the restoration was completed. After curing, the occlusal contacts were verified, and the restoration was polished (Figure 6).In addition to blocking out any darkened tooth structure, the supplemental blocking material can also be used for large Class III and IV restorations that exhibit light interference due to a lack of surrounding tooth structure and to hide the screw in screw-retained implant restorations.

Many dentists opt to use a specific composite resin in a particular clinical situation based on the shade, translucency, and physical properties of the tooth being restored. As a result, these dentists need to keep a variety of composites in the office for clinical use. Implementing a composite with excellent strength characteristics that uses the physical properties of light transmission to perfect shade matching may aid clinicians in creating predictable esthetic results as well as reduce the amount of composite resin that is inventoried and sometimes wasted in dental practices.