Effects of water flow on ablation rate and morphological changes in human enamel and dentin after Er:YAG laser irradiation

摘要

Purpose: To investigate the laboratory effect of Er:YAG laser on ablation rate and morphological changes in human enamel and dentin with varying water flow. Methods: 23 human third molars were sectioned in mesio-distal and buccal-lingual directions. The slabs were flattened and weighted on an analytical laboratory balance (control). A 4-mm2area was demarcated and the samples were randomly assigned into three groups according to water flow employed during the laser irradiation (1.0, 1.5, and 2.0 mL/minute). An Er: YAG laser was used to ablate enamel (80,22-J/cm2, 300 mJ/4Hz) and dentin (96.26-J/cm2, 250 mJ/4Hz). After irradiation, the samples were immersed in distilled water for 1 hour and then weighted again. The final mass was obtained and laser-irradiated substrate mass loss was calculated by the difference between the initial and final mass. Afterwards, specimens were prepared for SEM. Results: Data were submitted to ANOVA and Tukey's test (P 0.05). It was observed that the 2.0 mL/minute resulted in a higher mass loss, 1.0 mL/minute showed a lower mass loss, and 1.5 mL/minute demonstrated intermediate results (P 0.05). The increase of water flow promoted less melting areas and cracks. Furthermore, dentin was more ablated than enamel. It may be concluded that the water flow of Er:YAG laser and the substrates affected the ablation rate. Among the tested parameters, 2.0 mL/minute improved the ability of ablation in enamel and dentin, with less morphologic surface alteration. It has been shown that refrigeration with water is very important in the ablation process. The use of the adjusted water flow during irradiation of dental hard tissues by Er: YAG laser can increase the ablation rate and efficiency of substrate remoal and possible thermal damages to dental tissues.