Method: Twenty-four ceramic (Ivoclar) bars (9mm length x 6.5mm width x 4.0mm thickness) were made, and divided into 6 groups (n=4): Groups 1, 2 and 3 - acid etching with 5% hydrofluoric acid for 20 s; Groups 4, 5 and 6 – acid etching with 10% hydrofluoric acid for 20 s. Silane was applied on treated ceramic surfaces and the bars were bonded to a block of composite Tetric N-Ceram (Ivoclar) with RelyX U100 (3M ESPE). All specimens were stored in distilled water at 37oC for 24 hours. Groups 2 and 5 were submitted to 3,000 thermal cycles between 5°C and 55°C and Groups 3 and 6 were submitted to a fatigue test of 250,000 cycles at 2 Hz and 80N. Specimens were sectioned perpendicular to the bonding area to obtain beams with a cross-sectional area of 1mm2 (32 beams per group) and submitted to a microtensile bond strength test at a crosshead speed of 0.5mm/min. Data were submitted to ANOVA and Tukey’s post-hoc test (p<0.05).
Result: The bond strength values (MPa; mean±standard deviation) for the specimens stored 24 hours: Groups 1 (44.14±3.19) and 4 (45.13±2.23) were significantly higher than thermocycled Groups 2 (27.74±2.84) and 5 (28.37±1.92) and fatigue Groups 3 (25.51±2.37) and 6 (26.12±2.36). The thermocycled groups were significantly stronger than the fatigue groups. No significant difference was found between the two surface treatments.
Conclusion: The thermocycling and fatigue significantly decreased the microtensile bond strength for both ceramic surface treatments in relation to control groups.