Gold wire was used in dentistry in ancient times[2], and for filling cavities in the 19th century.[3] The material is suitable for dentistry because it is malleable, nearly immune to corrosion, and hard enough to form a biting surface that can be used for years.[citation needed] Gold was used before silver became available and has continued to be used for specialized purposes.[citation needed] Dental restorations are often made from a combination of precious metals.[citation needed]