Treatment of tooth fracture by medium energy CO2 laser and DP-bioactive glass paste: Thermal behavior and phase transformation of human tooth enamel and dentin after irradiation by CO2 laser

Acute trauma or trauma associated with occlusal disharmony can produce tooth crack or fracture. Although several methods are proposed to treat the defect, however, the prognosis is generally poor. If the fusion of a tooth fracture by laser is possible it will offer an alternative to extraction or at least serve as an adjunctive treatment in the reconstruction. The responses of soft tissues to lasers of different wavelengths are fairly well known, but the reactions of hard tissues are still to be understood. The purpose of this research was to study the feasibility of using a medium energy continuous-wave CO₂ laser and a low melting-point bioactive glass to fuse or bridge tooth fractures. The present report is focused on the first part of the research, the analysis of changes in laser-irradiated human tooth enamel/dentin by means of X-ray diffractometer (XRD), Fourier-transforming infrared spectroscopy (FTIR), differential thermal analysis/thermogravimetric analysis (DTA/TGA), and scanning electron microscopy (SEM). After CO₂ laser irradiation, there were no marked changes in the X-ray diffraction pattern of the enamel when compared to that before laser treatment. However, a small peak belonging to -TCP appeared at the position of 2=30.78°C. After being treated with CO₂ laser, the dentin showed much sharper peaks on the diffraction patterns because of grain growth and better crystallinity. -TCP and -TCP were identified after laser treatment. In the FTIR analysis, an HPO₄ ^-2 absorption band was noted before laser treatment disappeared after the irradiation. No significant change in the absorption band of HPO₄ ^-2 was found on the FTIR curves of enamel after laser treatment. The results of DTA/TGA indicated that loss of water and organic materials occurred in both enamel and dentin after laser treatment. Under SEM, melting and resolidification occurred in both enamel and dentin by medium energy of CO₂ laser. This implies that using a continuous-wave CO₂ laser of medium energy density to fuse a low melting-point bioactive glass to the enamel/dentin is possible. We believe these phase changes and thermal data can make a useful guide for future studies on the thermal interaction and bridging mechanism between the bioactive glass and enamel/dentin under CO₂ laser irradiation. © 2000 Kluwer Academic Publishers