Ablation studies of enamel tissue using pulsed HF laser

We describe studies of the interaction of ≅400 ns duration, multiline (2.6-3) μm HF laser with enamel tissue. The etch rate experiment showed an ablation threshold fluence of 47 Jcm^-2 but using the dispersion theory for optical coefficients of n and k for enamel at dominant laser lines, this value reduced to ≅25 Jcm^-2 making it more comparable with other investigations. The main mechanism of enamel ablation at 2.78 μm where its absorption is very high is thought to be due to microexplosive evaporation of water within enamel matrix i.e. thermomechanical decomposition. Also, using a photothermal deflection technique showed that at fluences below threshold a considerable amount of heat was emitted from the surface which was detected as a single compressive wave. The spectroscopic studies indicated that calcium was the main chemical element observed in plasma spanning from (420-620) nm.