2005 Volume 33 Issue 1 Pages 1-8
The purpose of the present study was to investigate laser welding characteristics for orthodontic wires using measuring tensile strength, characterizing morphology of the joint region, and determining phases by Micro-XRD. Beta-Ti, Ni-Ti and Co-Cr-Ni wires with cross-section dimensions of 0.016×0.022 inch were selected. Laser welding was performed at voltages ranging from 150 to 230 V. Tensile strength ranged from 167 to 416 MPa for the laser-welded Ni-Ti specimens and from 281 to 806 MPa for the laser-welded beta-Ti specimens. Tensile strength for laser-welded Co-Cr-Ni specimens ranged from 515 to 908 MPa, which was significantly lower than for control specimens (1421 MPa) joined by conventional silver-based soldering (P<0.05). For each wire type of specimen, increasing voltage of the laser welding procedure increased the localized fusing region. For most Micro-XRD spectra obtained at 1 mm distance from the joint of laser-welded Ni-Ti and beta-Ti specimens, intensities of the principal peaks for austenitic NiTi and beta-Ti increased, indicating that those regions were annealed by laser welding. Micro-XRD spectra obtained 2 mm distance from the joint for each wire type were similar to as-received specimens. In conclusion, laser-welding of beta-titanium and Co-Cr-Ni wires may be acceptable for clinical use, since the joints had sufficient strength and the original crystal structure of each wire type adjacent to the joint was not greatly altered.
