IR laser ablation of dental enamel: mechanistic dependence on the primary absorber

The mechanism of ablation of dental enamel was investigated at IR laser wavelengths from 9.3–10.6 μm and 2.7–3.0 μm. The mechanism of ablation varies markedly depending on whether the laser energy is coupled to the water (Er:YAG – λ=3.0 μm) or coupled to the mineral (CO2 – λ=9.6 μm). The ablation threshold occurs well below the melting point of dental enamel (1280°C) as indicated by SEM and time resolved surface temperature measurements during Er:YAG laser ablation. Conversely, ablation is initiated at temperatures above the melting point of hydroxyapatite during irradiation with 9.6 μm CO2 laser radiation. The ablation mechanism is apparently photomechanical in nature and water mediated at 2.94 μm, while near 9.6 μm, the mechanism is more indicative of thermal vaporization of the mineral matrix. Absorption spectra and SEM are used to support the hypothesis that the spatial distribution of water and mineral in the enamel microstructure is responsible for the mechanistic differences in ablation observed between the two IR wavelength regions.