Effect of Er:YAG laser irradiation distance on superficial dentin morphology

To assess in vitro the effect of Er:YAG laser irradiation distance on dentin surface morphology, by SEM.

60 sound human third molars were employed to obtain discs (approximately equal to 1mm thick), that were polished to standardize the smear layer. Discs were randomly assigned to six groups (n=10) and sequentially bisected. Five groups (including both disc halves of each sample) received Er:YAG laser irradiation (80mJ/2Hz) for 20s, according to the irradiation distance (11, 12, 14, 16 or 17mm) and one was the control group. In the lased-groups, one disc half was separated for superficial analysis without subsequent acid-etching and the other half received phosphoric acid for 15 seconds. In the control group, one disc half was treated with phosphoric acid and no superficial treatment was done in the other half. Specimens were prepared for SEM.

Er:YAG laser-irradiated specimens, regardless of the irradiation distance, showed an irregular and scaly surface, with intense ablation of the intertubular dentin, mainly when the irradiation was performed in the focused mode (12 mm). The smear layer was removed and dentin tubules were opened, however, no tubule enlargement was found, unlike the group that only received acid application. The irradiation with 17 mm resulted in a surface appearance more homogeneous than those presented with other distances closer to the focus. The subsequent acid-etching on the lased surfaces decreased the superficial irregularities with partial exposure and enlargement of dentin tubules, in all the tested irradiation distances.