Shoji Ohkawa

The influence of output current on the tensile strength of laser-welded titanium joints

The objective of this study was to examine the influences of the laser output current on the tensile strength of laser-welded titanium bar. Titanium bars of 3 mm in diameter were perpendicularly cut to 30 mm in length for the laser welding. Two bars were fixed to each other with a jig and welded vertically with the light of a laser beam. The tensile strengths of laser-welded titanium joints increased until the output reached 250 A, but decreased as the output current exceeded 250 A. The tensile strengths were significantly lower than that of non-welded parent metal.

CLSM and SEM quantitative analysis of surface topography of human teeth irradiated by Nd:YAG, Er:YAG and CO2 lasers

Abstract The quantitative analysis of surface roughness of cavities formed by three different lasers: Nd:YAG (wavelength 1.06 μm), Er:YAG (2.94 μm) and CO2 laser (10.6 μm) on dentin and enamel surfaces was carried out and compared using confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM). The three types of lasers were applied perpendicularly to the polished surface of human extracted caries-free molars. The highest value of surface roughness (Ra) was observed on enamel and dentin surfaces irradiated by the Er:YAG laser. Cracks were observed on dentin after CO2 laser irradiation. Er:YAG laser irradiation formed an imbricate-pattern while the Nd:YAG laser had a flake-like surface. A layer of globules representing melted material was observed in the cross-sectional view of dentin irradiated by the Nd:YAG laser. This area had a surface roughness of 0.88 μm, while a smooth area between the globules had Ra of 0.20 μm. Depth profile examination showed deeper cavities on surfaces irradiated by the Er:YAG laser. Quantitative analysis of surface roughness by both CLSM and SEM provided Ra by non-contact method, which was effective to evaluate the structural change of the tooth after laser irradiation.