The best bio-compatible dental casting alloy is:: (A) Co-Cr, (B) Ni-Cr, (C) Titanium alloy, (D) Gold
Answer is C. TITANIUM AND TITANIUM ALLOYS
In vitro evaluation of titanium biocompatibility, percentage attachment efficiency, and proliferation of human fetal fibroblasts and human gingival fibroblasts reveals that a surface layer of titanium oxide (Ti 2 O 3 ) has the ability to coexist with living tissues and organisms. Based on these studies one can conclude that titanium is relatively nontoxic, noninjurious, and not physiologically reactive. Titanium has a light weight, high  strength, and excellent durability when exposed to chemical agents. However, it is susceptible to attack by acidic fluoride products.
Phillips 12 ed page 126