An accurate and passive fit is necessary to maintain the functional integrity of implant prostheses. Poorly fitting implant restorations can result in biologic and mechanical failures. To improve the fit in prosthesis, various methods, such as laser welding and cast joining other than conventional soldering, have been developed. The purpose of this study was to measure and compare the strains produced by screw-tightening implant frameworks fabricated by three different joining methods; (1) laser welding, (2) cast joining, and (3) cast joining followed by laser welding of two half specimens and the secondary castings. In the third group, laser welding was employed to reinforce the weak cast joining. A research model incorporating eighteen strain gages was made to measure the fit of implant frameworks in three dimensions. Three implants with standard abutments aligned in an arc were fixed on the top ends of the L-shape aluminum bars of the research model. Three types of implant framework were placed on the abutments and screwed by a torque wrench using 10 Ncm. Under the conditions of this study, the following conclusions were drawn: 1. The three connecting methods yielded different results in regard to the accuracy of fit. 2. Cast joining group showed the smallest magnitude of total strain, followed by the laser welding group, and cast joining-laser welding. However, there was no significant difference between cast joining group and laser welding group. 3. The less magnitude of distortions were found in back-and-forth direction for cast joining group, in up-and-down direction for laser welding group, and in side-and-side direction for cast joining group and laser welding group than for the rest group or groups.
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