Influence of conditioning time on enamel adhesion

Objective: The aim of this study was to calculate enamel bond strengths of 4 self-etch adhesives in function of conditioning time. Methods and materials: Sixty proximal surfaces of 30 extracted human molars were roughened and assigned to 4 self-etch adhesives: AdheSE (Ivoclar Vivadent), Adper Prompt L-Pop (3M Espe), Clearfil SE Bond (Kuraray America), and Tyrian SPE/One-Step Plus (Bisco). Prime&Bond NT (Dentsply) was used as the total-etch control. For 30 surfaces, the adhesives were applied per the manufacturers' directions. For the remaining 30, enamel was conditioned for twice the time recommended by the manufacturer. Buildups were constructed with Filtek Z250 (3M ESPE). Bonded specimens were sectioned in sticks and tested to tensile failure. Data were analyzed with 2-way ANOVA and Duncan's test at P .05. The pH of the self-etch solutions and the phosphoric acid gel was measured with a pH meter. A correlation coefficient was computed to measure the linear association between pH and bond strengths. Results: Tyrian SPE and Prime&Bond NT, the adhesives whose acidic conditioners yielded the lowest pH, ranked in the highest subset regardless of application time. AdheSE and Clearfil SE Bond, which had the highest pH, were the only adhesives for which double application time resulted in statistically higher bond strengths than the recommended time. When means were pooled for application time, Tyrian SPE and Prime&Bond NT resulted in bond strengths that were significantly higher than those of the remaining adhesives. AdheSE resulted in statistically lower bond strengths than any other adhesive. A significant correlation was found between pH and mean bond strengths. Conclusion: Doubling the enamel conditioning time might increase bond strengths for specific self-etch adhesives. Keywords: acid-etching, dental bonding, enamel bonding, microtensile strength, self-etching primers