Casting alloys _____ allergy is common.

• A. Cobalt
• B. Chromium
• C. Nickel
• D. Titanium

Answer: (C)

Nickel allergy is the most common concern with dental casting alloys because many of these alloys contain nickel and can release nickel ions. When nickel ions enter contact with tissue, they can bind to proteins and form complexes that are recognized as foreign by the immune system. In individuals sensitized to nickel, this triggers a type IV hypersensitivity reaction, leading to dermatitis or mucosal irritation where the alloy contacts the tissues. Because this allergy is so prevalent, nickel-containing alloys are approached with caution in patients known to be nickel-sensitive, often opting for nickel-free alternatives like titanium-based or other non-nickel alloys. While cobalt and chromium can also cause sensitivities, they are less common than nickel in driving allergic reactions in the context of standard casting alloys, and titanium is typically praised for its excellent biocompatibility and low allergenicity.