A study of water-induced Er:YAG laser ablation of dental hard tissue.

摘要

Water induced ablation by the Er:YAG laser for different pulse widths was studied in dental hard tissue. Understanding the effects of exogenous water in the ablation of dental hard tissue for different pulse widths is important for the optimal and safe usage of water in dental treatment. In the free-running Er:YAG laser, the use of exogenous water drop lowered temperature rise in the pulp cavity to a safe level as compared to ablation without the use of exogenous water. The average ablation rate through a given thickness of the tooth was enhanced with water drop than the case of dry surface for thickness of about 1 mm or more. In the Q-switched laser, exogenous water drop enhanced the ablation rate and yielded minor mechanical damage in the ablated area. Exogenous water enhanced mechanical effects as measured by recoil momentum and pressure in the free-running and Q-switched laser, respectively. The difference of ablation rates in the different lasing modes, free-running and Q-switched, is attributed to the different ablation mechanism due to different pulse width.; In a separate study the effect of temperature rise propagation as a 'wave' for very short laser pulses was analyzed. In situations dealing with extremely fast rate processes such as those induced by a very short pulse laser, a Fourier heat conduction model shows the limitation in describing the temperature field. The wave nature of a thermal energy transport and a finite buildup time of heat flow were observed in the non-Fourier (hyperbolic) heat conduction model, and these phenomena were not recognized by the Fourier (parabolic) heat conduction model. The hyperbolic heat conduction model is expected to be a useful theoretical tool for the understanding of the thermal effects which occur in the ultra-short pulse range.