A comparison of the morphological changes after Nd-YAG and CO2 laser irradiation of dentin surfaces

The purpose of this study was to compare the morphological changes after Nd -YAG and CO2 laser irradiation on dentin surfaces with or without the smear layer. Eighty-one 3-mm-thick dentin specimens collected from the middle th ird of molar crowns were used. The dentin surfaces were ground to #320, #40 0, and #600 grit in series to create a smear layer. Half of the specimens w ere treated with 14% EDTA for 2 min to remove the smear layers. The lasers were applied on each specimen perpendicularly with l-mm focus distance to t he dentin surface for 4 s. The parameters for the Nd-YAG laser were 50 mJ, 100 mJ, and 150 mJ at 10 pps, 20 pps, and 30 pps, and for the CO2 laser wer e 2 W, 3 W, and 4 W at 5 ms x 20 pps, 10 ms x 10 pps, 20 ms x 20 pps, 50 ms x 2 pps, 100 ms x 2 pps, and 200 ms x 2 pps. The results showed that the N d-YAG laser caused crater and melting of the dentin surface, especially in dentin specimens with smear layers. The CO2 laser produced extensive cracki ng lines on dentin surfaces with a smear layer, whereas surface erosion and crater formation were found on specimens without a smear layer. In conclus ion, both the laser types and smear layer have a significant influence on t he morphological changes of dentin surfaces irradiated by lasers.