A prosthesis that contains zirconia and supplements a defective portion of a natural bone, and that is changed to a color approximate to that of the natural bone by a heat treatment after a ³-ray sterilization treatment. The color approximate to that of the natural bone has an L* value of 60 to 90, an a* value of -5 to 10, and a b* value of -5 to 10 in the L*a*b* color space. The highest temperature in the heat treatment is 100°C to 300°C. The prosthesis is a fixture of a dental implant embedded into and bonded to a natural bone, an abutment, an implant crown, and the like.