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 °C or 150 days of water storage with additional thermal cycling (37 500 thermal cycles between 5 °C and 55 °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 (α=.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.