Effects of Surface Treatments, Thermocycling, and Cyclic Loading on the Bond Strength of a Resin Cement Bonded to a Lithium Disilicate Glass Ceramic

Objectives: The aim of this present study was to investigate the effect of two surface treatments, fatigue and thermocycling, on the microtensile bond strength of a newly introduced lithium disilicate glass ceramic (IPS e.max Press, Ivoclar Vivadent) and a dual-cured resin cement. Methods: A total of 18 ceramic blocks (10 mm long X 7 mm wide X 3.0 mm thick) were fabricated and divided into six groups (n=3): groups 1, 2, and 3-air particle abraded for five seconds with 50-mu m aluminum oxide particles; groups 4, 5, and 6-acid etched with 10% hydrofluoric acid for 20 seconds. A silane coupling agent was applied onto all specimens and allowed to dry for five seconds, and the ceramic blocks were bonded to a block of composite Tetric N-Ceram (Ivoclar Vivadent) with RelyX ARC (3M ESPE) resin cement and placed under a 500-g static load for two minutes. The cement excess was removed with a disposable microbrush, and four periods of light activation for 40 seconds each were performed at right angles using an LED curing unit (UltraLume LED 5, Ultradent) with a final 40 second light exposure from the top surface. All of the specimens were stored in distilled water at 37 degrees C for 24 hours. Groups 2 and 5 were submitted to 3,000 thermal cycles between 5 degrees C and 55 degrees C, and groups 3 and 6 were submitted to a fatigue test of 100,000 cycles at 2 Hz. Specimens were sectioned perpendicular to the bonding area to obtain beams with a cross-sectional area of 1 mm(2) (30 beams per group) and submitted to a microtensile bond strength test in a testing machine (EZ Test) at a cross-head speed of 0.5 mm/min. Data were submitted to analysis of variance and Tukey post hoc test (p <= 0.05). Results: The microtensile bond strength values (MPa) were 26.9 +/- 6.9, 22.2 +/- 7.8, and 21.2 +/- 9.1 for groups 1-3 and 35.0 +/- 9.6, 24.3 +/- 8.9, and 23.9 +/- 6.3 for groups 4-6. For the control group, fatigue testing and thermocycling produced a predominance of adhesive failures. Fatigue and thermocycling significantly decreased the microtensile bond strength for both ceramic surface treatments when compared with the control groups. Etching with 10% hydrofluoric acid significantly increased the microtensile bond strength for the control group.