Objective The aim of this study is to evaluate whether the firing times affect the chroma of zirconia by adding rare-earth oxides. Methods Six kinds（S1, S2, S3, S4, S5, S6） of tooth-like yttria stabilized tetragonal zirconia polycrystal（Y-TZP） were available by introducing internal colorating technology, the color were gauged with ShadeEye NCC chromatometry instrument, and one -way ANOVA was used to analysis the color of each kind of tooth-like zirconia after 1, 2, 3, 4, 5 times firing individually. Results After 1, 2, 3, 4, 5 times firing respectively, the chromatic aberration ranged between 0.10-1.47 merely. The luminosity of three kinds（S1, S2, S6） of tooth-like zirconia were decreased（P＜0.05）, the luminosity of the other three kinds（S3, S4, S5） of tooth-like zirconia were not obviously changed（P＞0.05）, as for the hue and chroma, no significant differences were found（P＞0.05）. Conclusion There are no significant influence on the color of tooth-like Y-TZP after 1, 2, 3, 4, 5 times firing respectively, the chroma of yttria stabilized tetragonal zirconia polycrystal by adding rare-earth oxides are with high stability.
