| Infrared lasers are well suited for several therapeutic applications in dentistry including caries ablation, caries prevention through thermally induced chemical changes in dental enamel, and surface modification for enhanced bonding. A thorough understanding of the laser-tissue interactions is needed to determine effective treatment parameters and to prevent pulpal injury due to overheating. From an engineering perspective, the primary objective of this research was to design, implement, and validate a non-invasive time resolved radiometric system for the determination of the fundamental optical properties of highly absorbing materials/tissues. The primary objective of this research from a clinical perspective was to explore laser interactions with dental hard tissues to determine the absorption coefficients of dental hard tissues at clinically relevant wavelengths, the depth of modification of laser irradiated dental enamel, and the kinetic changes in the chemical composition of dental enamel during irradiation.; We used direct transmission measurements and pulsed photothermal radiometry (PPTR) measurements to determine the absorption and emission coefficients of dental enamel and dentin over a broad range of wavelengths in the infrared. To determine absorption/emission coefficients with PPTR, we compared numerical simulations of the thermal emission of laser irradiated tissue to experimental measurements of the thermal emission. The computer simulations were then used to estimate the depth dependence of the maximum temperature rise in the irradiated tissue. The modeled maximum temperature was compared to experimental data of chemical changes in dental enamel.; We found that the absorption coefficients of dental enamel at CO 2 laser wavelengths were much smaller than previously estimated. The absorption coefficients in dental enamel at 9.3, 9.6, 10.3 and 10.6 mum were determined to be 5250, 8000, 1100, and 800 cm-1 respectively. The absorption coefficients in dentin for the same four wavelengths were 5000, 6500, 1200 and 800 cm-1 respectively.; The treatment depth of dental enamel relied heavily on the penetration depth of the irradiating wavelength, the pulse duration of the laser and the fluence used to irradiate the tissue. By varying these three parameters, a modification depth can be achieved which ranges from less than a micrometer to the entire tooth. Using the computer simulations developed in this thesis, an estimate of the modification depth can be made without having to resort to experiment. |
