Phase, compositional, and morphological changes of human dentin after Nd :YAG laser treatment

Although techniques for repairing root fracture have been proposed, the pro gnosis is generally poor. If the fusion of a root fracture by laser is poss ible, it will offer an alternative to extraction. Our group has attempted t o use lasers to fuse a low melting-point bioactive glass to fractured denti n. This report is focused on the phase, compositional, and morphological ch anges observed by means of X-ray diffractometer, Fourier transforming infra red spectroscopy, and scanning electron microscopy-energy dispersive X-ray spectroscopy in human dentin after exposure to Nd:YAG laser. The irradiatio n energies were from 150 mJ/pulse-10 pps-4 s to 150 mJ/pulse-30 pps-4 s. Af ter exposure to Nd:YAG laser, dentin showed four peaks on the X-ray diffrac tometer that corresponding to alpha -tricalcium phosphate (TCP) and beta -T CP at 2 theta = 30.78 degrees/34.21 degrees and 32.47 degrees/33.05 degrees , respectively. The peaks of alpha -TCP and beta -TCP gradually increased i n intensity with the elevation of irradiation energy. In Fourier transformi ng infrared analysis, two absorption bands at 2200 cm(-1) and 2015 cm(-1) c ould be traced on dentin treated by Nd:YAG laser with the irradiation energ ies beyond 150 mJ/pulse-10 pps-4 s. The energy dispersive X-ray results sho wed that the calcium/phosphorus ratios of the irradiated area proportionall y increased with the elevation of irradiation energy. The laser energies of 150 mJ/pulse-30 pps-4 s and 150 mJ/pulse-20 pps-4 s could result in the al pha -TCP formation and collagen breakdown. However, the formation of glass- like melted substances without alpha -TCP at the irradiated site was induce d by the energy output of 150 mJ/pulse-10 pps-4 s. Scanning electron microg raphs also revealed that the laser energy of 150 mJ/pulse-10 pps-4 s was su fficient to prompt melting and recrystallization of dentin crystals without cracking. Therefore, we suggest that the irradiation energy of Nd:YAG lase r used to fuse a low melting-point bioactive glass to dentin is 150 mJ/puls e-10 pps-4 s.