The effect of speed sintering on the optical properties and microstructure of multi-layered cubic zirconia

Speed sintering was introduced to fabricate time-efficient chairside restorations, however, its influence on the microstructure and optical properties of zirconia is still unclear. This study investigated the influence of speed sintering on the microstructure and optical properties of ultra-translucent multi-layered cubic zirconia. Ultra-translucent cubic zirconia (Katana™ UTML; Kuraray Noritake Dental Inc., Aichi, Japan) was cut into a total of 80 specimens, twenty within each layer of the blank. The specimens were divided into 2 groups: speed and conventional sintering. The translucency parameter, opalescence, chromaticity, and color difference were recorded using a spectrophotometer. Scanning electron microscope images were used for crystallographic analysis. One-way ANOVA and Tukey's post-hoc test (p < 0.05) were used for data analysis. Speed sintering significantly reduced the translucency and opalescence compared to conventional sintering excluding the opalescence of the dentin layer. Chromaticity significantly decreased with speed sintering in less chromatic layers and significantly increased in more chromatic layers. Mean color change ranged between 0.65 and 1.25 across different layers. Mean crystal size decreased with speed sintering. With speed sintering, translucency, and opalescence decrease while chromaticity increases in the more chromatic layers. Additionally, no clinically perceptible color change was found compared to conventional sintering.