YAG laser nitriding treatment of the occlusal surface of artificial CP titanium teeth

Abstract

CP titanium is an appropriate material for the occulusal surface of artificial teeth. However, because of its low hardness, abrasion resistance must be improved in the occlusal contact region. We applied YAG laser nitriding to the occlusal surface to increase the strength and evaluated dimensional changes in the nitrided area. We found that cusps irradiated by the laser were evenly golden without macroscopic dimensional changes, and that many of the melted areas were surrounded by gold rings. Examination of the metal revealed dendrite-like structures in the surface layer, regions under the surface layer that had marked corrosion by the acid treatment, and needle or columnar crystals under the corroded areas. Compared with non-nitrided specimens, a very hard layer was present between the surface and the area 240μm below the surface, and the hardness was increased to a maximum of approximately 1, 063Hv. Analysis of the surface layer elements revealed virtually no nitrogen in the non-nitrided specimens, although there was approximately 4-10 weight percent nitrogen in the laser-nitrided specimens. Nitriding of the cusp area of CP titanium artificial teeth resulted in a mean change in the cusp height of ±11μm. Laser nitriding of artificial CP titanium teeth resulted in formation of a nitrided layer on the surface approximately 240μm thick. None the less, dimensional changes resulting from the nitriding treatment caused no clinical problems.