ABSTRACT
Indirect composites are designed to overcome the shortcomings of direct composites such as polymerization shrinkage and low degree of conversion. But, good adhesion of resin cements to indirect composites is still difficult. This research was designed to assess the effect of different powers of Er;YAG laser compared with sandblasting. On the micro tensil bond strength of resin cement to indirect composites. Specimens were prepred using dental resin composite [Gradia GC] and metallic mold [15×5×5 mm] and were cured according to the manufacturer's instructions. 24 blocks were prepared and randomly divided into 12 groups. G1:no treatment [as control], G 2-6: Er; YAG laser irradiation [2, 3, 4, 5, 6 Watt], G7: sandblast. Two composite blocks were bonded to each other with Panavia F.2. resin cement. The cylindrical sections with dimensions of 1 mm were tested in a microtensile bond strength tester device using 0.5 mm/min speed until fracture points. Data were analyzed using 2-way ANOVA and T-test. Interaction between lasers irradiation and sandblast treatments were significant [P<0.05]. Thus, T-test was used for comparing laser groups. T-test showed that when using laser with energies less than 150 mJ, there was no significant difference [P>0.05] whether samples were sandblasted or not. Samples which received 300 mJ of laser showed lower bond strength compared with no laser treatment. Other groups showed no significant difference [P>0.05]. It seems that application of sandblast with proper variables, is a good way to improve bond strength. Laser application had no influence in improving the bond strength between the indirect composite and resin cement