Title: Optical Properties of 80% Al2O3 and 20% ZrO2 ZTA Composites
Adolfo Lopes (Presenter)
University of São Paulo
Ernesto Jalkh, University of São Paulo
Kelli Monteiro, University of Sao Paulo
Luis Genova, IPEN
Paulo Cesar, University of Sao Paulo
Paulo Coelho, New York University
Paulo Lisboa-Filho, UNESP
Ana Flávia Borges, Bauru School of Dentistry
Estevam Bonfante, University of São Paulo
Objectives: This study was aimed to develop a experimental zirconia-toughened alumina (ZTA) with 80% Al2O3 and 20% ZrO2 (ZTA-ZPEX) and to compare its optical properties with a experimental translucent zirconia (ZPEX).
Methods: The composition characteristics that were used in the tested specimen preparation as well as the theoretical density values were calculated based on the density of alumina (3.986 g/cm3) and zirconia (6.10 g/cm3). Green disc-shaped specimens (12x1 mm) were obtained by uniaxial and isostatic ceramic powders pressing technique using a 15-mm-diameter matrix in order to compensate the sintering shrinkage (n=20/group). Then, the discs were sintered according to the following pre-established protocol: 1500°C for 1 hour with heating and cooling rate of 4°C per minute. After sintering, a two-sided polishing was performed with diamond discs (220, 120, 90, 40, 25, 9, 6 and 1 µm) and diamond suspensions up to 1 µm. The optical characterization was performed by means of reflectance tests on white and black background to determine the Contrast Ratio (CR) and the Translucency Parameter (TP) by color difference (△E).
Results: ZTA-ZPEX and ZPEX opacity values (CR) were 0.77(±0.002) and 0.99 (±0.05), respectively, without statistical significant difference between groups (p=0.0001). Regarding material color difference, ZTA-ZPEX △E was significantly lower than ZPEX (△E=0.19 (±0.03) and 10.19 (±0.43), respectively) (p<0.0001).
Conclusions: ZTA-ZPEX presented higher masking ability and lower translucency compared to the experimental translucent zirconia.