The effect of energy application sequence on the microtensile bond strength of different C-factor cavity preparations

This study investigated the effect of three equivalent radiant exposure energy application sequences (EASs): high intensity power (HIP: 1,177 mW/cm2, 40 seconds), low intensity power (LOP: 573 mW/cm2, 71 seconds) and ramp (RMP: 650 mW/cm2, 5 seconds, then the irradiance increases to 1047 mW/cm2, 37 seconds) on the microtensile bond strength (MTBS) in both low and high C-factor cavity preparations. Thirty Paradigm blocks (Z100) were mounted in stone, with their top surfaces parallel to the mounting block. High C-factor (HC = 3.8) Class I cavity preparations were then prepared in 15 of the Paradigm blocks using a computer-controlled specimen former. Low C-factor (LC = 1.8) Class II cavity preparations were prepared in the remaining 15 blocks by sectioning them perpendicularly using a slow-speed diamond saw. Five samples, one from each experimental group (3 EASs x 2 C-factors), were prepared and stored in the dark for 48 hours in distilled water at 37 degrees C prior to MTBS testing on the third day and on the remainder of the samples (n = 30). Mode of fracture was determined with a stereomicroscope at 20-40x magnification. The findings of this study indicated that HC, in combination with HIP, had significantly lower bond strength (27.54 MPa) than LC with HIP (51.39 MPa). On the other hand, there was no significant difference between high and low C-factors with the other EASs (LOP or RMP). There was also no significant effect for EAS (HIP, RAMP and LOP), with C-factor (HC or LC) held constant. The HIP-HC group had the highest percentage of adhesive (20%) and mixed adhesive (50%) failures (70% total). Adhesive and mixed adhesive failures occurred in other groups, but with lower percentages (RMP-LC: 40% total) (LOP-HC: 40% total).