Thermo-mechanical laser ablation of hard dental tissues: an overview of effects, regimes, and models

Derivation and predictions of the basic analytical model of thermo-mechanical laser ablation, treating the limit case of constant laser intensity, one-dimensional geometry, negligible heat diffusion and no debris screening, is summarized first as a reference point for further discussion. Each of the above requirements is then omitted in turn, to analyze additional effects observed under various experimental conditions. Scattering and absorption of the laser radiation in ejected debris is treated using a model that allows the debris extinction coefficient to vary dynamically during the ablation process, resulting in influence of pulse duration on the fluence dependence of predicted ablation crater depths. Next, the influence of heat diffusion on ablation efficiency and amount of thermal side effects is analyzed in a semi-quantitative way, leading to rule-of-thumb formulas that predict the ablation regime for a general ablation process from laser pulse fluence and duration as well as optical and thermal properties of the treated tissue. Influence of the laser beam profile on ablation crater depth and shape is demonstrated and discussed for the case of Gaussian beam profile. In the end, fiber-tip contact ablation in the presence of water spray is discussed as a counter-example of experimentally observed effects that - to our best knowledge - are still beyond the reach of quantitative understanding.