Objectives: Because of its high resistance to fracture and chipping it gets of interest to use zirconia (3Y-TZP) as fully-anatomical restoration material, either glazed or polished. Trying to improve the optical properties by increasing the translucency, manufacturer and laboratories use alumina-free zirconia material with coarse average grain-size (AGS). The objective of this investigation was to study the effects of the microstructure of different 3Y-TZP–types with and without alumina concerning AGS and homogeneity, as well as monoclinic fraction (M) and surface-roughening after aging.
Methods: Three alumina-containing 3Y-TZP materials (Zr-Al0.25, Zr-Al0.25II, Zr-Al0.25III) and three 3Y-TZP materials without alumina (Zr-Al0, Zr-Al0II, Zr-Al0III) of four different suppliers were densely sintered at different temperatures (1450°C, 1500°C, 1530°C, 1580°C, 1600°C) and varying dwell-times (30min, 120min, 180min, 240 min). The 1µm-polished surface was thermally etched at 1420°C, so that the microstructure could be analyzed by Scanning Electron Microscope (SEM). Afterwards, autoclaving of the samples at 134°C for 5h was applied. Before and after aging the surfaces were analyzed by X-RAY-Diffraction and M was calculated. The surface-morphology was further examined by SEM and Roughness-measurements.
Results: At 1530°C a coarsening of grains could be analyzed. At 1600°C an AGS of 1.00±0.15µm was measured. From 1450°C to 1500°C the AGS was in the range of 0.45µm. By simulated aging (autoclaving) accelerated phase-transition into M could be detected, for alumina-containing zirconia 5-12%, for alumina-free zirconia even 38-52%. The initial M-values are 1-6%. The formation of M corresponds to a significant surface-roughening (SR).
Conclusions: Aging is accelerated when alumina-free 3Y-TZP is fired at temperatures above 1500°C. The SR that occurs when M is built might increase the antagonist-abrasion and reduces the initial properties of the anatomical zirconia-restoration.