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The degradation of tetragonal zirconia polycrystalline (3Y-TZP) ceramics prepared by a novel film growth technique, and by sintering at 1400 °C, was evaluated for one year using two processes: (i) degradation under oral conditions in artificial saliva (37 °C and pH 6.8) and (ii) accelerated degradation by autoclaving at 134 °C at 0.2 MPa of pressure. X-ray diffraction analysis of 3Y-TZP ceramics sintered at 1400 °C showed a phase transformation (tetragonal to monoclinic) in 3Y-TZP ceramics after the fifth month in artificial saliva. After 12 months in artificial saliva, there was ∼11% of monoclinic phase present in 3Y-TZP ceramics, but only ∼2% of monoclinic phase in samples that were subjected to accelerated degradation for 5 h. No correlation was found between the level of ageing during accelerated degradation and degradation in artificial saliva. There was no degradation of 3Y-TZP ceramics prepared by a novel film growth technique, independently of the degradation method used, which suggests that this material could be used for dental prosthetics.