Effect of Fe₂O₃on optical properties of zirconia dental ceramic

To evaluate the effect of Fe₂O₃on the optical properties of yttria-stabilised tetragonal zirconia (Y-TZP) dental ceramic when added, and to determine the correct content required to mimic the natural dentin.

Disc-shaped Y-TZP specimens (0.50 ± 0.01 mm in thickness) containing various contents of Fe₂O₃were fabricated by cold isostatic pressing and pressureless sintering, and then compared with human dentin slices (n = 40) under different moisture conditions. The visible light transmittance and colour parameters were recorded by a computer-controlled spectrocolourimeter. Sintered density and microstructure were investigated with the Archimedes' method and scanning electron microscopy (SEM), respectively.

With the reduction of moisture in dentin slices, the direct transmittance dropped from 1.58% to 0.87%. The direct transmittance of coloured zirconia specimens, ranging from 1.22% to 1.40%, covered the range of dentin. With increasing Fe₂O₃content, the L* value of the coloured specimens decreased from 88.95 to 84.18, while b* increased from 3.43 to 12.02. The relative densities of all groups were over 99% of the theoretical value. The SEM indicated that zirconia with various amounts of Fe₂O₃retained the compact microcrystalline tetragonal structure.

Small amounts of colourant additions affected the colour and the transmittance slightly, but had no influence on the sintered density and microstructure. Y-TZP could be improved by the control of colourant additives of Fe₂O₃in order to mimic the natural colour of dentin and to obtain a better aesthetical appearance of restorations, especially when the content was around 0.08 wt%.