Application of titanium alloys to porcelain fused to metal crown

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Titanium is an attractive dental restorative material because of its excellent characteristics, however it is difficult to cast. Beta-stabilized titanium alloys have lower fusion temperatures than pure titanium. For dental clinical use, these alloys must be able to bond to dental porcelains because of the esthetic demands of dentistry. Eighteen binary titanium alloys were examined : Ti-Cr (15, 20, 25 wt%), Ti-Pd (15, 20, 25 wt%), Ti-Ag (10, 15, 20 wt%), Ti-Cu (5, 10 wt%), Ti-Fe (5, 10, 15 wt%) and Ti-Mn (5, 10, 15, 20 wt%). As controls, pure titanium and a gold alloy were also examined. Bond strengths were evaluated according to ISO 9693. The elastic modulus was also measured for each. The titanium alloy composition had a significant effect on alloy elastic modulus, but it had little effect on the bond strength to porcelain. The bond strengths for all the experimental alloys were similar to those of the two control alloys (Pure titanium and gold alloy) and were higher than 25 MPa, the minimum value specified in ISO 9693. These findings indicate that the experimental alloys exhibited sufficient shear bond strength for use in metal-ceramic restorations.In this study, some specimens (Ti-15wt%Pd and Ti-20wt%Pd) deflected upon cooling, even after the bond test. The thermal expansion value of these alloys was not much different from that of the other alloys. The next study investigated the cause of this deflection by analyzing the thermal expansion/shrinkage curve.Because the beta to alpha phase transformation and the stress developed from the shrinkage of the porcelain simultaneously occurred, these alloys were permanently deformed (I.e., they underwent creep), resulting in the deflected specimens.