Influence of welding (Laser or TIG) on marginal misfit (two and three-dimensional), detorque strength in prosthetic screws, mechanical fatigue, corrosion and stress induced to the prosthetic abutment of implant-supported prostheses

The aim of this study was to evaluate titanium casted structures behavior, welded by LASER (Light Amplification by Stimulated Emission of Radiation) and TIG (Tungsten Inert Gas), on marginal misfit (two and three-dimensional), prosthetic screws detorque strength, mechanical fatigue, corrosion and stress induced to the prosthetic mini abutment analogs. Fifty structures were casted in commercially pure titanium (cp-Ti); twenty frameworks (n=20) simulating multiple prostheses of three elements; and thirty dumbbells (n=30). From the frameworks were fabricated two type of index, simulating a marginal misfit of 200µm. One index was fabricated in special plaster to the development of stress analysis, and other in epoxy resin to the development of marginal misfit analysis (two and three-dimensional), detorque strength, mechanical fatigue and corrosion. Before and after welding procedures (LASER or TIG) were developed the following evaluation: marginal misfit analysis, by optical microscope (two-dimensional) and X-ray microtomography (three-dimensional); induced stress analysis on prosthetic mini abutment analogs, by extensometric technique; and measurement of prosthetic screws detorque strength. The welding procedures were made with the following parameters: LASER (370V/9ms); TIG (36A/60ms). After welding procedures (LASER or TIG), the frameworks were submitted to cyclic mechanical (280N; 106 cycles; 2 Hz) by oblique compressive load to evaluation of the detorque strength after the cycling. The longevity of the welded structures was also evaluated by mechanical fatigue testing, and the corrosion behavior by electrochemical tests of electrochemical impedance spectroscopy and potentiodynamic polarization. The results were analyzed statistically (one-way ANOVA / Tukey HSD test / Student-t test (? = 0.05)). Both the welding procedures decreased the marginal misfit level (two and three-dimensionally), increased the detorque strength and decreased of stress induced on prosthetic mini abutment analogs. However, after the mechanical cycling there was decrease of detorque strength of prosthetic screws. The structures welded by LASER had high fatigue resistance than the structures welded by TIG. The impedance spectroscopy test was only significant for frameworks welded by TIG, compared with intact and LASER welded LASER frameworks. It is concluded that welding procedures had influence on marginal fit, providing more stability to the implant-supported system. The mechanical cycling had influence on prosthetic screws stability, being necessary periodic following up to tighten and/or exchange of prosthetic screws. The titanium casted and LASER welded structures were more fatigue resistance than that TIG welded structures. Electroless, LASER welding procedure have better corrosion behavior compared to TIG welding procedure (AU)