Not long after composite resins were first recommended as a posterior restorative system, the Europeans suggested using them as an indirect system. Two reasons were given. First of all it was recognized that as compared to the conventional amalgam restoration, the Class II composite was considerably more difficult to accomplish. Problems commonly encountered included less than ideal marginal adaptation, general anatomic form and loose and open proximal contacts and secondary caries. Secondly, limited laboratory studies suggested that subjecting the light-cured restoration to a subsequent heat treatment actually increased the wear resistance appreciably.
Unfortunately most of the inital systems were failures. Either the restoration fracured under stress, discolored considerably or simply did not show any enhancement in wear resistance. Now however, with the elimination of oxygen by curing in an inert atmosphere, the resultant restorations not only are considerably more esthetic than the direct composite resin counterpart, but the wear resistance is far superior to any other format. In fact, the resistance to wear over a ten-year period has been shown to approximately only one micron per year more than enamel.
These excellent findings now justify the use of laboratory processed composite resin on the occlusal table as a potential substitute for porcelain when the clinical condition arises. One of the most practical uses of this indirect resin is the coronal restoration of implants. In the case of the polymer, the energy of mastication is critically abosrbed by the restoration rather than transmitting this energy into the implant and into the surrounding periosseous alveolar structure. By comparison, the ceramic restoration absorbs very little of this energy and disperses it accordingly. Many clinicans have realized this relationship betwen material and energy transfer and are now using such materials as belleGlass NP to restore the coronal component of their dental implant.
While this is good news for the clinician who is making every effort to enhance the clinical longevity of his/her implant, there are relatively few materials that clinically have been tested for this purpose. Presently there are only three: these include belleGlass NP (Sybron/Kerr), Sculpture Plus (Zahn Schein) and Cristobal Plus (Dentsply/Ceramco). Undoubtedly the future will bring us more systems but like the ones already identified, clinical trials will have to be conducted to justify their acceptance.
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