2007 Volume 70 Issue 3_4 Pages 212-221
Application of water spray is standard when using the Er:YAG laser for the clinical ablation of teeth. It is because the ablating efficiency improves. However, its role is controversial. The reason is that the water molecule is originally included in the hard tissues of teeth. We studied the role of water molecules in the laser-ablation of porous ceramics made of hydroxyapatite (HAP) and fluoroapatite (FAP). The sample specimens were immersed in water to fill the pores before irradiation by the laser. In order to distinguish the effect caused by molecules in the specimens from that caused by water molecules outside, we used light and heavy water during the laser irradiation. This is because light water absorbs the photons emitted by the Er:YAG laser while heavy water does not. We found that the water contained in the specimens played an important role in ablation of the HAP. The rate of ablation caused by the water molecules outside the specimens was no less than that caused by molecules inside for each apatite. When the imprints of the ablation on the HAP and FAP specimens were compared, it was found that the hydroxyl radicals in HAP made a large contribution to the laser-ablation.
