Penetration Depth of Nd:YAG Laser into Dental Casting Alloys

Objective: This study investigated the effect of laser welding conditions [voltage (V) and spot diameter (mm)] on the penetration depth into dental casting alloys. Methods: Castings (3 x 8 x 50 mm) were prepared from the metals used in this study: commercially pure titanium (CP Ti)(ASTM Grade 2, Titanium Industry, TX), Ti-6Al-4V (ASTM Grade 5, Titanium Industry, TX), Ti-6Al-7Nb(T-Alloy Tough, GC Co., Japan), cobalt-chromium alloy (Co-Cr)(Vitallium, Austenal, IL) and Type IV gold alloy (Ney-Oro, Ney Dental International, CT). Two blocks of metal were butted against one another on the 8.0 x 50 mm surfaces. They were then laser-welded at their interface (Neolaser L, GIRRBACH Dental Systems, Germany) under the following conditions: voltage of 160 - 340 V and spot diameter of 0.4 - 1.6 mm. After welding, the blocks were divided, and the penetration depth of the laser into each alloy was measured. Data were analyzed using ANOVA at the P<0.05 level of significance. Results: The penetration depths of the laser were follows: CP Ti (0.29 - 6.45 mm), Ti-6Al-4V (0.32 - 5.24 mm), Ti-6Al-7Nb (0.34 - 5.65 mm), Co-Cr (0.24 - 6.15 mm) and Type IV gold alloy (0.12 - 5.22 mm). The voltage (F=10.02, p=.000) and spot diameter (F=25.09, p=.000) affected the penetration depth of laser into the metals tested. When the voltage increased and the spot diameter decreased, the penetration depth increased for each metal. Conclusion: Selecting suitable conditions of the laser welding to obtain sufficient penetration depth for the optimal thickness of metal used is important when welding prostheses. This study was supported in part by NIH grant DE 11787 and BCD Intramural Grant Y2001-Z.