Deflection load characteristics of laser-welded orthodontic wires

Objective: To compare the deflection load characteristics of homogeneous and heterogeneous joints made by laser welding using various types of orthodontic wires. Materials and Methods: Four kinds of straight orthodontic rectangular wires (0.017 inch x 0.025 inch) were used: stainless-steel (SS), cobalt-chromium-nickel (Co-Cr-Ni), beta-titanium alloy (beta-Ti), and nickel-titanium (Ni-Ti). Homogeneous and heterogeneous end-to-end joints (12 mm long each) were made by Nd:YAG laser welding. Two types of welding methods were used: two-point welding and four-point welding. Nonwelded wires were also used as a control. Deflection load (N) was measured by conducting the three-point bending test. The data (n = 5) were statistically analyzed using analysis of variance/Tukey test (P < .05). Results: The deflection loads for control wires measured were as follows: SS: 21.7 +/- 0.8 N; Co-Cr-Ni: 20.0 +/- 0.3 N; beta-Ti: 13.9 +/- 1.3 N; and Ni-Ti: 6.6 +/- 0.4 N. All of the homogeneously welded specimens showed lower deflection loads compared to corresponding control wires and exhibited higher deflection loads compared to heterogeneously welded combinations. For homogeneous combinations, Co-Cr-Ni/Co-Cr-Ni showed a significantly (P < .05) higher deflection load than those of the remaining homogeneously welded groups. In heterogeneous combinations, SS/Co-Cr-Ni and beta-Ti/Ni-Ti showed higher deflection loads than those of the remaining heterogeneously welded combinations (significantly higher for SS/Co-Cr-Ni). Significance (P < .01) was shown for the interaction between the two factors (materials combination and welding method). However, no significant difference in deflection load was found between four-point and two-point welding in each homogeneous or heterogeneous combination. Conclusion: Heterogeneously laser-welded SS/Co-Cr-Ni and beta-Ti/Ni-Ti wires provide a deflection load that is comparable to that of homogeneously welded orthodontic wires. (Angle Orthod. 2012;82:698-702.)