Comparison between novel strength-gradient and color-gradient multilayered zirconia using conventional and high-speed...

To investigate and compare the mechanical and optical properties of novel strength- and color-gradient multilayered zirconia and the impact of conventional and high-speed sintering.

Following zirconia materials were analyzed and compared: the high-speed sintered Katana Zirconia Block STML (4Y-TZP, KZC), the conventionally sintered Katana Zirconia Disc STML (4Y-TZP, KZL) and IPS e. max ZirCAD Prime (5Y-TZP/3Y-TZP, EZL). As control group acted the crystallized lithium disilicate ceramic IPS e. max CAD (ELC). Monolithic single molar crowns were fabricated and half of them were aged in a chewing simulator with human enamel antagonists (1.2 × 10⁶ cycles, 50 N, lateral movement of 0.7 mm, 5/55 °C). The fracture load was tested in a universal testing machine (N = 96/n = 12). The two-body wear was determined using 3D matching of pre- and post-scans (N = 48/n = 12). Translucency (N = 36/n = 10) was evaluated with UV/Vis spectrophotometer. Data was analyzed using Kolmogorov-Smirnov test, one-way ANOVA followed by post-hoc Scheffé test, unpaired t-test and Weibull analysis (p < 0.05).

Zirconia groups showed higher fracture load than ELC (p ≤ 0.001). Initially, all zirconia materials ranged in the same values (p > 0.05). After chewing simulation, EZL showed higher fracture load than KZC (p < 0.001) and KZL (p = 0.043). Zirconia materials showed no material loss, whereas the ELC showed the volumetric wear of 0.334 ± 0.34 mm³ and vertical wear of 0.155 ± 0.07 mm. Enamel antagonist wear ranged in the same values (p = 0.083-0.906). The translucency values within each zirconia material showed significant differences between the enamel and the dentin layers (p < 0.001).

The novel strength and color-gradient multilayered zirconia showed higher mechanical properties than lithium disilicate ceramic. The high-speed sintering of zirconia showed neither a negative impact on the fracture load nor on the two-body wear. However, the optical properties and the reliability of zirconia is lower than those of highly translucent lithium disilicate ceramic.