Light deposition in dental hard tissue and simulated thermal response

Near-IR (approximately 1 micron) lasers are presently used for a variety of intra-oral applications including dental hard tissue ablation, although the light intensity distribution and subsequent heating of the hard tissue are still poorly understood. This paper presents a detailed numerical study of the scattered light intensity distribution along with the corresponding predicted thermal response. The calculations are based on recently published scattering and absorption data for dental hard tissue around 1 micron. Our simulations indicate strongly enhanced energy deposition and concomitant heating near the dentino-enamel junction (DEJ), mainly due to the higher absorption in dentin. We predict from 10 to 20 times higher internal temperatures near the DEJ compared with the surface. For example, for 50-ms pulses of 5-J energy on a 3-mm-diameter spot (approximately 1 kW/cm2 or approximately 50 J/cm2), one can expect internal temperatures near the DEJ in excess of 100 degrees C. Elevated temperatures are predicted to extend far into the dentin, endangering the vitality of the pulp several millimeters below the surface. Our results are compared with published experimental data taken under similar conditions and are found to be in good general agreement. The results of this study do not contradict recently reported ablation of dentin with Nd:YAG laser radiation by contact fiber probes. In this case, the irradiation intensities are 3 to 4 orders of magnitude higher, so plasma formation and plasma shielding of the interior of the tooth are likely.