Influence of pretreating enamel on the durability of resin bonds.

STATEMENT OF PROBLEM: Minimally invasive restorations adhesively bonded to prepared enamel have been well established clinically. However, studies on the durability of noninvasive restorations are still lacking. PURPOSE: The purpose of this laboratory study was to evaluate the tensile bond strength (TBS) of a luting resin and its durability to differently pretreated enamel with 2 different etching procedures. MATERIAL AND METHODS: The proximal surfaces of human third molar teeth were embedded in custom-made holders with an autopolymerizing composite resin. The enamel was pretreated according to the protocol of the respective group (n=16): Minimally invasively prepared (M), unprepared (N), and airborne-particle abraded (O); enamel was either etched with phosphoric acid followed by applying a self-etching primer (PT) or conditioned with a self-etching primer only (T). The bonding surfaces of the specimens were perpendicularly luted to acrylic resin tubes filled with a composite resin (Clearfil F II) with a luting resin (Panavia V5). Each of the 6 groups was further divided into 2 subgroups with either 3-days of water storage at 37 degrees C or 150 days of water storage with additional thermal cycling (37 500 thermal cycles between 5 degrees C and 55 degrees C). TBS was evaluated with a universal testing machine. All specimens underwent failure mode analysis. Statistical analysis was performed with a 3-way ANOVA, followed by 2-way ANOVAs and separate 1-way ANOVAs. For pairwise comparisons of groups, the Tukey post hoc test was performed (alpha=.05 for all tests). RESULTS: Statistical analysis revealed that the enamel preparation had no significant effect on TBS after artificial aging when etched with phosphoric acid (P=.520). Conditioning with a self-etching primer only showed significantly lower TBS than groups etched with phosphoric acid for the same preparation after 150 days (P=.014 for minimal preparation, P=.028 for no preparation, and P<.001 for airborne-particle abrasion), and artificial aging did not significantly affect TBS (P=.763). The mean +/-standard deviation values ranged from 9.8 +/-8.1 MPa (OT) to 36.4 +/-7.4 MPa (MPT) after 150-day storage. CONCLUSIONS: Etching of enamel is essential for optimal resin bonding, but the preparation of enamel or artificial aging had no influence on TBS.