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 toot h crack or fracture. Although several methods are proposed to treat the def ect, however, the prognosis is generally poor. If the fusion of a tooth fra cture by laser is possible it will offer an alternative to extraction or at least serve as an adjunctive treatment in the reconstruction. The response s 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 cont inuous-wave CO2 laser and a low melting-point bioactive glass to fuse or br idge tooth fractures. The present report is focused on the first part of th e research, the analysis of changes in laser-irradiated human tooth enamel/ dentin by means of X-ray diffractometer (XRD), Fourier-transforming infrare d spectroscopy (FTIR), differential thermal analysis/thermogravimetric anal ysis (DTA/TGA), and scanning electron microscopy (SEM). After CO2 laser irr adiation, there were no marked changes in the X-ray diffraction pattern of the enamel when compared to that before laser treatment. However, a small p eak belonging to alpha-TCP appeared at the position of 2 theta = 30.78 degr ees C. After being treated with CO2 laser, the dentin showed much sharper p eaks on the diffraction patterns because of grain growth and better crystal linity. alpha-TCP and beta-TCP were identified after laser treatment. In th e 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 treatmen t. The results of DTA/TGA indicated that loss of water and organic material s occurred in both enamel and dentin after laser treatment. Under SEM, melt ing and resolidification occurred in both enamel and dentin by medium energ y of CO2 laser. This implies that using a continuous-wave CO2 laser of medi um 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 ma ke a useful guide for future studies on the thermal interaction and bridgin g mechanism between the bioactive glass and enamel/dentin under CO2 laser i rradiation. (C) 2000 Kluwer Academic Publishers.