Comparative in vitro study of the bond strength of composite to enamel and dentine obtained with laser irradiation or acid-etch

The shear bond strength of composite resin on enamel and dentine was compared after acid-etch or irradiation by Er:YAG and Nd:YAP lasers. Forty-eight extracted molars were selected. Dentine and enamel samples were prepared by buccal and lingual surface sectioning to expose a plane enamel or dentine surface. Samples (n=12) were randomly assigned to eight groups. In groups 1 and 5, enamel and dentine surfaces were etched with a 37% phosphoric acid solution. In groups 2 and 6, surfaces were irradiated by Er:YAG laser at an energy of 200 mJ and 4 Hz for enamel and 140 mJ and 4 Hz for dentine. In groups 3 and 7, irradiation was performed by Nd:YAP laser at 310 mJ and 10 Hz for enamel and 240 mJ and 10 Hz for dentine. Groups 4 and 8 served as controls. A cone of composite was bonded perpendicularly onto the prepared surfaces using the Scotch Bond Multipurpose adhesive system. Each sample was then stored in physiological serum at 37 degrees C for one week and thermocycled. Shear bond strength was determined on a universal testing machine. Composite-enamel and composite-dentine interfaces were examined by scanning electron microscopy and microanalysis. Shear bond strength was greater on dentine and enamel after acid-etch than laser radiation. These treatments could be ranged in the following order: acid-etch, laser Er:YAG and laser Nd:YAP. Differences between groups were significant for enamel, whereas no significant differences were found for dentine between acid-etch and Er:YAG laser-irradiation (Kruskal-Wallis test). Thus, laser preparation did not improve bonding to enamel and dentine.