Influence of Layer and Sintering Temperature on the Optical Properties of Multilayered Zirconia Materials.

OBJECTIVE: To evaluate the translucency and color difference of the individual layers of two multi-layered zirconia materials at different sintering temperatures and to compare them with lithium disilicate.

METHODS: Multi-layered zirconia systems with four distinct layers were selected for this study: DD cube ONE ML (4Y-TZP), DD cubeX2 ML (5Y-TZP); and compared with IPS e.max CAD HT (LS2). Plate-shaped A2-shade specimens were obtained from LS2 and individual layers of both zirconia materials. Individual layers were then divided equally into three different sintering temperatures:1300°C, 1450°C, and 1600°C. The TP and ΔE were determined by a spectrophotometer. SEM images were taken. Data was analyzed using SPSS 24.0 software with a p-value ⟨0.05.

RESULTS: A significant difference was found in TP and ΔE values amongst all types of ceramic materials. Different sintering temperatures yielded distinct TP and ΔE values when both zirconia materials were tested and compared with LS2. Finally, TP and ΔE values were different amongst the zirconia layers.

CONCLUSION: Sintering temperature, type of ceramic material and different zirconia layers significantly affected the optical properties.

CLINICAL SIGNIFICANCE: Multi-layered zirconia materials possess a unique gradient effect that could efficiently enhance the esthetics of monolithic zirconia restorations. However, the sintering condition should be optimized.