Objective: Ti-6Al-7Nb alloy has excellent biomechanical properties and therefore, has the potential to be applied to removable partial denture (RPD) frameworks. However the alloy is not sufficiently rigid, in terms of elastic modulus, to apply it to the major connector (MC). In our preliminarily study, strengthening designs, which have potential to improve rigidity of the MC, were found by finite element analysis (FEA). The objective of this study was to evaluate the rigidity of the strengthening designs as suggested by the FEA using fabricated RPD. Method: The 3 MC strengthening designs were chosen - wide (0.8mm x 16mm), thick (1.0mm x 10mm), and reinforced designs (0.8mm x 10mm with center thickened)-which theoretically had rigidity comparable to conventional Co-Cr MC (0.8mm thick x 10mm width). Five different Kennedy II maxillary RPD, including a conventional Co-Cr RPD and Ti-6Al-7Nb RPD with and without the MC strengthening designs, were evaluated for rigidity. In total, 25 dentures (5 for each design) were fabricated. Three strain gauges were placed on the MC and a pressure sensor was placed on the mucosal surface of the denture base. A load of 30N was applied vertically to the artificial tooth with each RPD placed on a plastic model and the strains and the pressure were measured by these sensors. Results: The strain on the middle portion and the pressure on the mucosal ridge of all of the 3 strengthening designs were comparable to those of the Co-Cr RPD (15.7±6.4µƒÃ,25.1±6.7kPa), while the data for the Ti-6Al-7Nb RPD without the strengthening design (34.8±17.1µƒÃ,40.6±23.7kPa) were significantly larger than those of the Co-Cr RPD (ANOVA, p<0.05). Conclusion: These results suggest that the strengthening designs could improve rigidity of the Ti-6Al-7Nb MC. However patients' response to the oral sensor should also be taken into consideration.

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