Fit of cast commercially pure titanium and Ti-6Al-4V alloy crowns before and after marginal refinement by electrical discharge machining

Statement of problem. Titanium has been suggested as a replacement for alloys currently used in single-tooth restorations and fixed partial dentures. However, difficulties in casting have resulted in incomplete margins and discrepancies in marginal fit. Purpose. This study evaluated and compared the marginal fit of crowns fabricated from a commercially pure titanium (CP Ti) and from Ti-6Al-4V alloy with crowns fabricated from a Pd-Ag alloy that served as a control. Evaluations were performed before and after marginal refinement by electrical discharge machining (EDM). Material and methods. Forty-five bovine teeth were prepared to receive complete cast crowns. Stone and copper-plated dies were obtained from impressions. Fifteen crowns were cast with each alloy (CP Ti, Ti-6Al-4V, and Pd-Ag). Marginal fit measurements (in micrometers) were recorded at 4 reference points on each casting with a traveling microscope. Marginal refinement with EDM was conducted on the titanium-based crowns, and measurements were repeated. Data were analyzed with the Kruskal-Wallis test, paired t test, and independent t test at a 1% probability level. Results. The Kruskal-Wallis; test showed significant differences among mean values of marginal fit for the as-cast CP Ti crowns (mean [SD], 83.9 [26.1] mum) and the other groups: Ti-6Al-4V (50.8 [17.2] mum) and Pd-Ag (45.2 [10.4] mum). After EDM marginal refinement, significant differences were detected among the Ti-6Al-4V crowns (24.5 [10.9] mum) and the other 2 groups: CP Ti (50.6 [20.0] mum) and Pd-Ag (not modified by EDM). Paired t test results indicated that marginal refinement with EDM effectively improved the fit of CP Ti crowns (from 83.9 to 50.6 mum) and Ti-6AI-4V crowns (from 50.8 to 24.5 mum). However, the difference in improvement between the two groups was not significant by t test. Conclusion. Within the limitations of this study, despite the superior results for Ti-6Al-4V, both groups of titanium-based crowns had clinically acceptable marginal fits. After EDM marginal refinement, the fit of cast CP Ti and Ti-6Al-4V crowns improved significantly.