Effect of resin-based dental composite marginal repair techniques on enamel bonding

Tooth-colored dental fillings known as resin-based dental composite (RBDC) possess excellent esthetic and functional properties, which explains their extensive use in dental practices. Regardless of their improved success and longevity, RBDC fillings are still subject to failure due to different reasons including recurrent decay and fracture. Repair of failed RBDC fillings rather than complete replacement offers a minimally invasive approach that could prevent further loss of tooth structure, save time and preserve resources.

The margins of the failed RBDC fillings usually involve part of the filling and the tooth structure, which makes the repair a challenging procedure. The repair procedure basically involves partial removal of the defective portion of the filling or decay, if present, and placement of new RBDC filling. This is accomplished by treating the surface of the old existing RBDC filling to help creating a bond between the old and new RBDC. This could include the application of abrasive particles (aluminum oxide) that mechanically abrade the surface creating a rougher surface. The surface of old RBDC could be treated both mechanically and chemically by the use of a modified-reactive abrasive particles (CoJet) and application of a chemical agent (silane). Then an adhesive, which creates a bond between the old and new RBDC filling, is applied. The adhesive is also responsible for creating a bond between the new RBDC and the involved part of the tooth structure (enamel).

Many studies have investigated the effect of these repair surface treatments on the old RBDC; however, data regarding their effect on enamel are controversial and inconclusive. The unintentional contact of some of these surface treatments with the enamel may negatively affect its bond to the new repairing RBDC. However, it is possible that such effect could be alleviated by exposing enamel to phosphoric acid (etching) after being contaminated. Therefore, this in-vitro study was conducted to evaluate the effect of the RBDC marginal repair techniques (aluminum oxide abrasives, CoJet/silane) on enamel bonding and test the theory that etching enamel after contamination with the repair techniques will eliminate any possible “adverse” effect of those techniques.

The results of this current study indicated that enamel bonding was not significantly affected when enamel was etched after being exposed to the repair techniques included in this study, then bonded with the adhesive. However, when enamel was immediately bonded with the adhesive after being exposed to one the repair techniques (CoJet/silane) without etching, enamel bonding was significantly lowered.

Within the limitation of this in-vitro study, the inadvertent exposure of enamel to CoJet/silane during the repair of RBDC fillings may negatively affect the enamel bonding especially when enamel is not etched with phosphoric acid after being exposed to CoJet/silane. Further investigations that include the examination of the seal and long-term performance of the enamel-adhesive joint are essential.