Abstract: Differing reports exist on the dependence of ablation rate in hard dental tissue on Er:YAG laser energy. In order to clarify this point we have carried out a systematic study of Er:YAG laser ablation rates in enamel and dentin extraorally with and without water spray cooling. Our findings confirm the existence of saturation of ablation rates at high laser energy densities which has been already previously attributed to plasma shielding. The drilling efficiency and the saturation effect have been found not to depend significantly on the presence of water spray. It is worth pointing out that a standard water spray, as used for mechanical drilling very efficiently eliminates any charcoaling, without reducing laser drilling efficiency. Diameters of ablated holes have been found to increase with laser energy also above the saturation of drilling efficiency. Measurements of the dependence of the ablation efficiency on pulse duration indicate that there is an optimal pulse duration for Er:YAG laser drilling of approximately 200 $mu@s.!5
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