Adhesive Evaluation by Brushing Tests for Hydroxyapatite Films Fabricated on Dentins Using a Water Mist Assisted Er:YAG Laser Deposition Method

Hydroxyapatite (HAp) is one of the main structural components in tooth. Therefore, the HAp is an ideal material to repair tooth substances. However, it has not yet been realized that tooth enamel and dentin are artificially repaired using the HAp in operative dentistry. We have proposed and developed a tooth restoration technique with intraoral laser ablation using an Er:YAG (Erbium: Yttrium-Aluminum-Garnet) laser in order to fabricate HAp films on tooth surfaces in the atmosphere at room temperature. Although HAp thin films were formed on dentin surfaces using the Er:YAG laser deposition method, it has still been unclear how is the mechanical durability of the HAp film on tooth substances. In the present study, we conducted brushing tests to evaluate the durability of adhesion between the HAp film and dentin. To form HAp layers on dentin surfaces, an ablation phenomenon was induced by the Er:YAG laser irradiated to the target of α-tricalcium phosphate (α-TCP) under humid conditions. The deposited layers were hydrolyzed by dripping artificial saliva on the surface at 37 degrees Celsius for 24, 48, 72, 120, and 168 hours to create HAp films. The films hydrolyzed for more than 48 hours were attached on the dentin surface after the brushing tests. This result indicates that the α-TCP layer deposited on the dentin surface changes into a crystallized HAp material by the hydrolyzation for more than 48 hours. The crystallization of the film possibly contributes to the high adhesive durability of the HAp film deposited on the dentin.