Effect of Grinding Time on the Grindability of Cast Titanium

Objective: This study investigated the effect of grinding time on the grindability of cast titanium. Methods: Two types of cast titanium [Commercially pure titanium (CP Ti: ASTM grade 2) and Ti-6Al-4V (ASTM grade 5)] were used. Wax patterns (3 mm x 8 mm x 30 mm) were invested in a magnesia investment material (Selevest CB, Selec Co., Japan). The casting was made using a dental centrifugal casting machine (Ticast Super R, Selec). Grindability (n=4) was evaluated as volume loss (mm³) when grinding the 3.0 mm surface with a SiC wheel (703-120, Brasseler) (100 gf) at a speed of 1250 m/min. Grinding was continued for 5, 10, 15, 30, 60, 70, 80 or 90 seconds. In estimating the a-case thickness, the microhardness near the cast surface was measured (n=4). The depth of each cut was determined in SEM (n=2). Data were analyzed using ANOVA followed by Tukey's test (a = 0.05). Results: There were significant differences between CP Ti and Ti-6Al-4V in the grindability at each corresponding time (p<0.05). The a-case thickness of the CP Ti and Ti-6Al-4V was 298 mm and 154 mm, respectively. The amount ground from each metal consistently increased with the duration. The grinding speed of the cast CP Ti within its a-case seemed to be higher when compared to that in the interior of its casting. On the other hand, the grinding speed in the a-case of the cast Ti-6Al-4V and the interior of its casting was similar. Conclusion: The ease of grinding of the a-case on the CP Ti and the Ti-6Al-4V was very similar. The grinding of the interior of the CP Ti, as compared to that of the Ti-6Al-4V, was more difficult because of its higher ductility. This study was partially funded by NIH/NIDCR grant DE11787 and the Baylor Oral Health Foundation.