Posterior composite resins can be considered as having two distinctly different personalities.
One that is properly and carefully inserted into the cavity preparation is characterized by excellent performance. As mentioned in Dr. Wiggin’s letter, the composite resin restoration has the potential for supporting tooth structure and thereby reducing the potential for fractured cusps.
Furthermore, as he states, the potential for bonding the composite resin to the preparation permits the operator to be considerably more conservative in terms of cavity design. This, of course, can lead to better tissue response, since in many cases it may not be necessary to extend the preparation to the gingival tissue.
When placed properly and in accordance with the concepts supported by clinical research, the posterior composite resin can last as long as a corresponding amalgam restoration. In addition, the potential for esthetics is, of course, far superior.
The other personality of posterior composite resin restorations is far different. When handled inappropriately, this material can create serious clinical conditions far worse than amalgam. These include leakage, interfacial staining, secondary caries and opened or loose proximal contacts. Under less-than-optimum conditions, the longevity of the restoration is far less than amalgam.
The rules associated with a clinically acceptable posterior composite have now been well-defined. The first of these, of course, is moisture control. While there are numerous ways to accomplish this goal, the best by far is the use of a properly placed rubber dam.
Salivary contamination of the surfaces during the bonding procedure or placement of the composite can create major problems. Contamination by the proteins of the salivary fluid will jeopardize satisfactory bonding to the walls of the preparation that, in turn, will lead to micro-leakage, as well as postoperative sensitivity.
There is still another facet of composite resins that has not been thoroughly discussed in the literature. This concerns the relationship of the antagonist cusp to the surface of the composite restoration. Undoubtedly, the greatest potential adversary of a well-placed posterior composite is the tip of the opposing cusp.
In this regard, a pointed or strongly angulated cusp tip in direct opposition to the surface of the composite resin can accelerate the rate of wear. While different types of materials behave in various ways, a strong contact can produce an appreciable amount of localized wear. The extent of attrition will depend on the load applied and the surface area of the contacting cusp tip.
When such a condition does exist, it is recommended that the clinician slightly recontour this cusp tip (enameloplasty) to increase the surface area of contact. The amount of reshaping should not be great enough to remove the contact. Perhaps the best way to accomplish this procedure is to modify the cusp tip prior to initiation of the cavity preparation.
Finally, Dr. Wiggin was concerned about the fact that, as opposed to amalgam, composite resins tend to encourage bacterial growth. It should be pointed out that such a condition only occurs when there is an avenue between the restoration and the walls of the preparation. In the case of sealants, bacterial growth is unlikely if the margins of the sealant are intact.
As suggested by Dr. Wiggin, posterior composite resins can serve as an excellent substitute for amalgam if close attention is paid to details of placement. A combination of the superior materials now offered to the clinician in association with conservative cutting of teeth (minimal invasive dentistry) and careful manipulation of the associated materials will routinely generate an excellent restoration.
