Efeito de um cimento resinoso dual em baixa e alta viscosidades na adesão e no comportamento mecânico em fadiga de zircônias de segunda e terceira geração

Abstract

The present dissertation is composed of two studies. The aim of the first study was to evaluate the effect of different viscosities of a resin cement on the bond strength (µSBS) of second (3YTZP) and third generation (4Y-PSZ) zirconia ceramics after aging. Thus, slices of both ceramics were made and embedded in PVC cylinders, and distributed into 4 groups according to 2 factors: viscosity of the resin cement (high or low) and zirconia ceramic (3Y-TZP or 4Y-PSZ). The bonding surfaces of the ceramics were sandblasted with aluminum oxide (45 µm) and primer was applied. Cylinders (Ø = 1.15 mm; height = 1.0 mm) of resin cement (n = 20) were cemented onto the ceramics with the aid of starch matrices and subjected to aging conditions (thermocycling - 12,000 cycles - plus 120 days of storage). The µSBS test was then performed. The surface topography and failure pattern of the ceramics were analyzed by scanning electron microscopy (SEM). Statistics were performed by ANOVA (2 factors) and Tukey's post-hoc test. Atomic force microscopy (AFM) analysis (topography and fractal dimension) was also performed. The results showed that ceramics (p = 0.90) and viscosities (p = 0.35) had no significant effect on bond strength. All groups were statistically similar, and the failure pattern was predominantly adhesive. The SEM and AFM topography were similar between the two ceramics after surface treatment, as well as the fractal dimension. The second study aimed to evaluate the effect of different viscosities of a resin cement (low and high) on the mechanical fatigue behavior of zirconia (3Y-TZP and 4Y-PSZ). The ceramic discs were randomly allocated to 4 groups (n = 20) according to the study factors: resin cement viscosity (low or high) and ceramic type (3Y-TZP or 4Y-PSZ). Thus, the cementation surfaces of the discs were sandblasted with aluminum oxide particles (50 µm) and primer was applied. They were then cemented onto a dentin analogue (fiberglass-reinforced epoxy resin). The cemented sets were subjected to fatigue testing using the step-stress method (initial load of 200 N; 100 N increment; 10,000 cycles; 20 Hz). In addition, Weibull analysis and complementary analyses of topography, fractographic characteristics, bond interface analysis, and Raman spectroscopy for phase analysis were performed. For the fatigue test, 3Y-TZP showed better mechanical behavior than 4Y-PSZ, regardless of the viscosity of the resin cement used. In addition, 3YTZP with low viscosity cement showed better mechanical performance compared to the other groups, while 4Y-PSZ with both viscosities of resin cement showed inferior fatigue performance compared to the other groups and were similar to each other. All groups showed similar Weibull modulus.