Effect of light source direction and restoration thickness on tensile strength of a dual-curable resin cement to copy-milled ceramic

Purpose: To evaluate the effects of exposure duration and source direction on bond strength of a dual-curable resin cement to copy-milled ceramic Materials and Methods: Ceramic blocks (Vita Celay Blanks) were cut into 1 mm, 2 mm and 3 mm thick slices. Following silanization (Tokuso Ceramic Primer), the slices were bonded using dual-cure resin cement (Bistite II) and subjected to one of four photo-curing strategies: no light-cure (control), 20 seconds light-cure from one direction, 120 seconds from one direction, and 20 seconds from each of six directions. After 24-hour water storage at 37degreesC, the microtensile bond strengths and resin cement Knoop Hardness of the bonded specimens were determined. The data were analyzed using two-way ANOVA and Fisher's PLSD test at a confidence level of 95%. Specimen failure modes were determined using a laser-scanning confocal microscope. Results: The KHN of the control group was significantly lower than those of the light-cured groups (P< 0.05). There were no significant differences in bond strength and microhardness when the 1 and 2 mm thick ceramic slices were light-cured for either 120 seconds from one direction, or for 20 seconds from six directions (P> 0.05). However, when ceramic thickness increased from 2 to 3 mm, significant reduction in bond strength occurred when light-cure was applied for 120 seconds from one direction, but not when applied for 20 seconds each from six directions (P< 0.05).