歯科領域レーザー治療のトピックス

Abstract

Soldering has been chiefly used for jointing dental prosthetic materials. Titanium is very difficult to solder because it is highly susceptible to oxidation. The recent development of an infrared heater soldering system is expected to make titanium soldering easier. However, because this soldering system uses a solder different from the conventional solder, it may cause problems in the oral cavity such as low resistance to corrosion. Titanium soldering requires prior fixation with the investment material. Therefore, the author recently attempted laser welding of titanium. In this attempt, normal pulse Nd-YAG lasers (M801A and M802, NEC) were used. The weld strengths of titanium plate specimens obtained by two different welding techniques were compared. With a laser beam (70mm in focal distance, 0.8mm in diameter), two titanium plates (40×10×3mm), superimposed each other 2mm at the end, were welded either by lap seam welding or by spot welding under the following settings: pulse width, 4ms (for spot welding) or 3ms (for lap seam welding); output, 12.5J/P (for spot welding) or 6.3J/P (for lap seam welding). The load required to tear off the joint by pulling for the spot-welded specimen was 90kgf in average, while that for the lap-seam-welded specimen was more than 120kgf in average, where the breakage of the base metal often arose in the proximity of the weld. A major factor hampering the utilization of titanium for prosthesis is the difficulty in processing. If laser welding is introduced to titanium, the dental application of titanium will widen.