Optical properties of CAD-CAM monolithic systems compared: three multi-layered zirconia and one lithium disilicate system

OBJECTIVE: this in vitro investigation aims to evaluate and compare optical properties of three types of esthetic CAD-CAM monolithic multi-layered zirconia materials with a control (conventional lithium disilicate, IPS e. max CAD). METHODS: Four monolithic CAD-CAM ceramic materials were investigated: Ceramill Zolid® FX Multilayer (ZF), IPS e. max® ZirCAD MT Multi (ZM), Katana® STML (KS) and one lithium disilicate glass-ceramics as a control (IPS e. max® CAD LT; LC). A total of 72 (15 × 15 × 1 mm) samples were CAD CAM fabricated and sintered based on sample-size power calculations, and each material comprised 18 samples. The translucency and opalescence parameters with the contrast ratio were evaluated with a dental spectrophotometer over the backgrounds of black and white. The data were analyzed by ANOVA, then Bonferroni post hoc comparison test was made between groups. The statistical significance was set at p < 0.05. RESULTS: Zirconia materials revealed lower optical properties than the lithium disilicate control LC (P < 0.05). TP values ranged from 14.174 to 20.439. No differences were detected between the zirconia products in terms of TP and CR (P = 1.000). OP values ranged from 5.068 to 10.097. The lowest OP values were found statistically significant for ZF followed by KS and ZM (P = 1.000). LC had the highest TP and OP values, as well as the lowest CR (p < 0.05). CONCLUSIONS: The optical properties of monolithic zirconia systems tested here are still lower than those of lithium disilicate glass-ceramics. The only difference observed between the monolithic CAD CAM zirconia materials, was for the low opalescence parameter for the ZF. CLINICAL SIGNIFICANCE: Multi-layered monolithic zirconia systems have better esthetics by shade layers resembling natural tooth color gradients. CAD-CAM technology allowed for in-office milling and shaping of restorations using these systems. This study reports on their optical properties affecting human vision/perception of natural tooth shade to conclude about their use in the esthetic zones.