Impact of glazing on wear, fracture load, and optical properties of a new fully crystallized lithium disilicate ceramic material.

OBJECTIVES: Lithium disilicate (LDS) based glass ceramics are indispensable materials in the field of prosthetic dentistry due to their strength and excellent esthetics. Recently, novel fully crystallized LDS for the milling process have been introduced to the market, requiring only chairside polishing before delivery. Since limited data is available about subjecting this material to glazing, this study aimed to evaluate the wear properties, fracture resistance, and optical properties of the newly introduced fully crystallized LDS after glazing.

METHODS: Lithium disilicate glass-ceramics (fully crystallized (LiSiCAD) and partially crystallized types (EmaxCAD), of shade A3, were used in the present study. The fully crystallized specimens were subjected to a glazing firing cycle in a furnace (LiSiCAD-G) and compared to a polished fully crystallized counterpart (LiSiCAD-P, negative control) and a glazed partially crystallized LDS (EmaxCAD, positive control). Rectangular-shaped ceramic specimens (n = 10, 12 × 6.5 × 1.5 mm) and enamel antagonists were used to test the wear resistance in a specially designed wear machine built at the Department of Oral Technology, University of Bonn, Germany. The volumetric enamel loss of antagonists was measured by means of overlapping virtual 3D models derived from micro-CT scans for the teeth before and after the wear test. The weight loss of ceramic specimens in milligrams was measured after 100,000 and 200,000 wear cycles. A spectrophotometer was used to calculate the CIELAB color parameters of the ceramic specimens against black and white backgrounds to measure the translucency. Fracture resistance was also assessed after thermodynamic fatigue using a universal testing machine until fracture at a 1 mm/min crosshead speed. Statistical analysis was performed using one-way ANOVA and the significance level was set at α = 0.05.

RESULTS: EmaxCAD and LisiCAD-G groups showed significantly higher mean ceramic weight loss after 100,000 cycles (2 ± 0.3 mg and 1.93 ± 0.2 mg, respectively) than LisiCAD-P group (0.78 ± 0.19 mg). Glazed LiSiCAD specimens demonstrated significantly higher ΔE values from shade A3 compared to polished LiSiCAD. There was no significant difference in ΔE between LiSiCAD-G and EmaxCAD. For fracture resistance, no significant difference was observed between LiSiCAD-G and LiSiCAD-P before or after aging.

CONCLUSIONS: The glazed fully crystallized LDS was superior to the partially crystallized one with regard to wear resistance but showed more color changes than the polished fully crystallized one. Furthermore, polishing of fully crystallized LDS could still be considered a better option than glazing when aesthetics is a primary prerequisite.