Ablation studies of enamel tissue using pulsed HF laser

We describe studies of the interaction of /spl cong/400 ns duration, multiline (2.6-3) /spl mu/m HF laser with enamel tissue. The etch rate experiment showed an ablation threshold fluence of 47 Jcm/sup -2/ but using the dispersion theory for optical coefficients of n and k for enamel at dominant laser lines, this value reduced to /spl cong/25 Jcm/sup -2/ making it more comparable with other investigations. The main mechanism of enamel ablation at 2.78 /spl mu/m 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.