Photoelastic and mechanical analyses of welded cp titanium implant-supported frameworks

Objective: Aiming to obtain frameworks with better fit, this study compared one-piece casted frameworks with frameworks obtained by two different soldering techniques: Laser-welding and TIG (Tungsten Inert Gas).

Method: Thru photoelastic analysis and flexural strength tests, the stress distribution around implants and the mechanical resistance of the frameworks were evaluated. Fifteen commercially pure titanium frameworks were obtained using a steel matrix, with four external-hexagon (3.75x13mm) implants. The frameworks were divided into three groups: GI or control - one-piece casted frameworks; GII - Laser welded frameworks; GIII - TIG welded frameworks. For stress analyses a photoelastic model, reproducing the steel matrix was manufactured with photoelastic flexible resin. Each framework was screwed with 20Ncm torque to the photoelastic models implants. Using a circular polariscope the order of the isochromatic fringes around the implants was obtained. Maximum sheer stress was determined through the “stress optical law”. A mechanical test of flexural strength was performed at the hanging arms joints of each framework, using a universal testing machine (Instron 4411 Corp.Canton, Mass.) with a speed of 2 mm/min, load cell 500Kgf and maximum length of 5.00mm. The data were submitted to ANOVA followed by Tukey test (p=0.05).

Result:  No difference was observed on shear stress of the welding techniques. The casted group showed lower stress values than the TIG welded group. On the mechanical test the casted group presented higher compressive resistance (291,91N/mm²), followed by laser (224,20N/mm²) and TIG welded ones (123,65N/mm²).

Conclusion: It is concluded that the conventional casting technique provides more mechanically resistant infrastructures than the welding techniques, with similar or lower stress to the supporting implants.