Methods: In this in vitro study 24 caries free recently extracted human premolars were used. All were extracted for orthodontic reasons. They were divided in three groups of 8 teeth each, all of them were prepared, acid etched (orthophosphoric acid 37%, 15 minutes, cleaned for 30 seconds) and/or laser irradiated (Er:YAG, 120 mJ, 4Hz impacts) and then filled. Teeth were cut mesio-distally just above the pulpar chamber and 2mm above. In the center of this section a cavity was done. The bond strength was evaluated with a Monsanto Tensometer Machine in megapascales (MPa) to evaluate the bond strength in the axial walls of the preparation. Statistical analysis included ANOVA and Scheffé test.
Results: The average bond strength in the axial dentin surface after acid etching was 13.94 +- 1.31 MPa (group A), after laser irradiation was 12.78 +- 2.12 MPa (group B) and with both procedures combined was 20.92 +- 3.29 MPa (group C). There were no differences between groups A and B (p=0.63). Between group C and others groups the difference was highly significant (p<0.001).
Conclusions: Combining both techniques (laser irradiation and acid etching) provides significant better bond strength between the axial dentin surface and the resin material than each technique alone. No other studies that evaluate the bond strength to axial forces in laser irradiated dentine were found in the literature.