The effect of pulsed Nd–YAG laser irradiation on acid resistance of dentin

Abstract The purpose of this study was to examine the effect of tip–object distance in Nd–YAG laser irradiation on the acid resistance and morphological change of dentin. Freshly extracted human premolars were used. Each crown was cut in half transversally. Samples were randomly assigned to five groups as follows. Group 1: noncontact laser irradiated with 100 mJ, 10 pps (tip–object distance was approximately 2 mm). Group 2: contact laser irradiated with 100 mJ, 10 pps. Group 3: noncontact laser irradiated with 200 mJ, 10 pps. Group 4: contact laser irradiated with 200 mJ, 10 pps. Group 5: control. For acid resistance testing, they were individually immersed in acetic buffer solution (0.2 M, pH 4.2). The amount of dissolved Ca 2+ in each solution was determined by sequential plasma spectrometry. The laser-irradiated dentin surface had morphological characteristics such as a cracker or lava. The dissolved Ca 2+ from lased dentin was significantly less than that of the control group. In the group of noncontact lased dentin, the dissolved Ca 2+ lased with 100 mJ is less than that of lased with 200 mJ. In the contact lased group, the dissolved Ca 2+ lased with 200 mJ is less than that lased with 100 mJ. These results lead the optimum pulsed Nd–YAG laser-irradiated condition of different tip–object distance on acid resistance of dentin.