Structural changes of Er:YAG laser-irradiated human dentin.

Objective: The aim of this study was to investigate the phase, compositional, and morphological changes of Er:YAG laser-irradiated dentin.

Background Data: To date, nothing comprehensive has been reported about the phase and compositional changes of human dentin after Er:YAG laser irradiation.

Methods: The human dentin was irradiated by Er:YAG laser with irradiation energies from 300 mJ/pulse-10 pps-10 sec to 700 mJ/pulse-10 pps-10 sec with and without water spray. After irradiation, the specimens were analyzed by means of x-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM).

Results: After exposure to Er:YAG laser, dentin showed no phase changes on the x-ray diffractometer. In Fourier transform infrared analysis, two absorption bands at 2200 and 2015 cm(-1) could be traced on dentin treated by Er:YAG laser with irradiation energies beyond 300 mJ/pulse-10 pps-10 sec and without water spray. The OH(-) band disappeared at 1630 cm(-1). Scanning electron micrographs revealed that laser energy of 500 mJ/pulse-10 pps-10 sec was sufficient to prompt melting and recrystallization of dentin crystals.

Conclusions: Our study demonstrated that Er:YAG laser irradiation on dentin with water spray would not significantly change the structure and composition. Therefore, water cooling is important for reducing the thermal effect of Er:YAG laser.