Evaluation of optical properties of zirconia infrastructure systems using kubelka-munk analyses

Zirconia ceramics are commonly used due to the high mechanical properties, biocompatibility and resistance against biting forces. When compared to other ceramic systems, the opacity of zirconia was greater than that of any of the alumina, spinell, and feldspathic ceramic materials studied. Substrate materials should be translucent in order to obtain maximum aesthetic results. The aim of this study was to compare color and translucency properties of zirconia-based infrastructure systems. Five different zirconia based systems; Rainbow, Rainbow-translucent, Ice Zirkon, Prettau and Lava were evaluated in the present study (n=16/group). Discs within each group with 14 mm diameter and 0,5 mm thickness were randomly divided into two groups where half of the specimens (n=8) were veneered with 1mm thick feldspathic porcelain, while the other half (n=8) were left intact. A PR705 spectroradiometer was used to measure spectral reflectance. Reflectance spectra were converted to L*, a*, and b* (CIELAB) values. Kubelka-Munk theory was then used to determine the inherent color and translucency of each zirconia system. Data were statistically analyzed using one-way ANOVA followed by post-hoc Ryan-Einot-Gabriel-Welsch-Q test (α=0,5). Results from the current study has shown that Rainbow-translucent zirconia core specimens showed the lowest translucency values while Prettau zirconia core specimens showed the highest. Similar to the unveneered specimens the the lowest and the highest ΔE values were obtained for Rainbow-translucent and Prettau zirconia groups, respectively. Within the limitations of this study, it can be concluded that Kubelka-Munk theory can be used to determine the translucency parameter. Statistically significant differences were observed between translucencies of different zirconia core materials. For clinical applications; when the tooth adjacent to the restoration is translucent or translucent restoration is required higher translucency material can be preferred, whereas the tooth adjacent to the restoration is opaque or a restoration with high opasity is needed to mask the discolored structures, the lower translucency zirconia ceramics should be preferred.