Thermal Interactions Between Dentin and Tunable Short-Pulsed CO₂ Laser

Abstract

Surface modification with laser irradiation has been investigated for the prevention of root surface caries. In this study, we investigated the rise in temperature and the change of optical characteristics of irradiated dentin to clarify the thermal effect of laser irradiation on the dentin surface modification. A tunable transversely excited atmospheric (TEA) CO² laser was used. Laser wavelengths were 9.3, 9.6, 10.3, and 10.6μm. Laser energy density were 0.4-4.8 J/cm². The number of irra diated pulses was set to 1-50. The rise in temperature was measured by a radiation thermometer. The optical spectra of irra diated dentin were measured by a Fourier transform infrared spectrometer. The maximum rise in temperature depended on the laser wavelength and the laser energy density. The maximum rise in temperature showed the maximum value at the wavelength of 9.6μm. The maximum rise in temperature decreased with the increase in the number of pulse irradiation, because the laser irradiation to the dentin changed the optical characteristics of the dentin. The absorption peak shifted from 9.6μm to 9.1 and 9.4μm. This change depended on the laser energy density and means improved acid resistance. We showed that the wavelength of 9.6μm, which has the shortest optical penetration depth, induced the effective surface modification with the least thermal damage to dentin.