The performance of sol-gel silica coated Y-TZP for veneered and monolithic dental restorations.

OBJECTIVES: The purpose of the study was to characterize the microstructure, constituents, and mechanical properties of mono and bilayered zirconia specimens infiltrated with silica by the sol gel method. METHODS: 180 zirconia discs (14-mm diameter) were divided in 3 groups (n = 60) according to thickness (1.2, 0.5 mm) and further divided in two groups (n = 30) according to treatment (infiltrated or not). Disk thickness was 1.2 mm for the control samples. Veneering feldspathic porcelain had two thicknesses (0.5 mm and 1 mm) at the tops of the zirconia discs. All groups were subjected to the biaxial flexural test in an aqueous medium. Weibull analysis was performed for determination of the Weibull modulus (m) and characteristic strength (σ0). The specimens were characterized by SEM and EDS and XRD. Hardness and elastic modulus were measured by nano-indentation and pulse-echo methods, respectively. Fracture toughness was determined by the nano-indentation technique. A scratch test was used for evaluation of the adhesion between the zirconia and porcelain. RESULTS: There was less variability (higher Weibull modulus) in the infiltrated monolithic specimens; biaxial flexural strength was not statistically higher in the veneered infiltrated specimens and was decreased for the 1-mm veneered infiltrated group. The diffractograms showed formation of ZrSiO4 crystal phase. Hardness also increased in the infiltrated monolithic zirconia, whereas fracture toughness decreased. Adhesion between zirconia and porcelain was superior in the non-infiltrated monolithic specimens. CONCLUSIONS: Infiltration increased the structural homogeneity and hardness of the monolithic zirconia, but it reduced fracture toughness, and the adhesion to porcelain. CLINICAL SIGNIFICANCE: Within the limitations of the present study, it is possible to recommend the infiltration of silica gel in zirconia only for monolithic restorations.

Bioinspired silica-infiltrated zirconia bilayers: Strength and interfacial bonding.

Conventionally veneered zirconia restorations are susceptible to chipping and spalling of the veneering material. The novel translucent zirconias were developed to overcome such issues, although layered zirconia restorations can be re-designed to improve mechanical performance. Thus, the aim of this study was to analyze the strength and structural reliability of zirconia bilayers using conventional (porcelain ceramic under tensile stress) and bioinspired (zirconia under tensile stress) configurations. Sol-gel silica infiltration served as a smooth transition between the zirconia and veneering porcelain. Failure mode and interfacial adhesive mechanism were analyzed using scratch test and interfacial indentation. Bilayered specimens were produced for biaxial flexural testing with Y-TZP and pressed ceramic, which were further divided into four groups (n = 30): Conventional (C), Infiltrated conventional (IC), Bioinspired (B) and Infiltrated bioinspired (IB). The results of biaxial flexural strength tests were analyzed by Weibull analysis (95% CI) for determination of the Weibull modulus (m). The infiltration layer was characterized by XRD and SEM, FEG-SEM and EDS. The bioinspired infiltrated group was the most reliable (m = 9.59), although the fine damage of veneered conventional (conventional) zirconia demonstrated its superior resistance to scratching and debonding. Therefore, the filling of superficial defects by zirconia silicate demonstrated the need for mechanical retention for better porcelain adhesion.

A Novel Method of Synthesizing Graphene for Electronic Device Applications.

This article reports a novel and efficient method to synthesize graphene using a thermal decomposition process. In this method, silicon carbide (SiC) thin films grown on Si(100) wafers with an AlN buffer layer were used as substrates. CO2 laser beam heating, without vacuum or controlled atmosphere, was applied for SiC thermal decomposition. The physical, chemical, morphological, and electrical properties of the laser-produced graphene were investigated for different laser energy densities. The results demonstrate that graphene was produced in the form of small islands with quality, density, and properties depending on the applied laser energy density. Furthermore, the produced graphene exhibited a sheet resistance characteristic similar to graphene grown on mono-crystalline SiC wafers, which indicates its potential for electronic device applications.