Caracterização topográfica e mecânica de laminados cerâmicos com diferentes reduçōes incisais.

Abstract

The mechanical properties of ceramics are directly related to the clinical success of ceramic veneers. Thus, the objective of this study was to evaluate the residual stress, hardness, surface roughness and to determine fracture load for veneers made from two glass- ceramics with different incisal reductions (1 mm and 4 mm). Fifty-two specimens of feldspar ceramic (FE) and zirconia-reinforced lithium silicate (SZ) veneers were prepared and divided into 4 groups (n = 13): FE1 - with 1 mm incisal reduction; FE4 - with 4 mm incisal reduction; SZ1 - with 1 mm incisal reduction; SZ4 - with 4 mm incisal reduction. The veneers were obtained through the computer- aided design and manufacturing method and cemented in human upper central incisors. All specimens were analyzed before and after polishing using an optical microscope and surface roughness were measured by the roughness meter. The indentation method was used to measure the residual stress and Vickers hardness and the compression test was performed to determine the fracture load. After fracturing, the fractographic analysis of the specimens was performed using optical and scanning electron microscopes. For roughness, the Tukey test was applied for the ceramic material and the Mann-Whitney test for before and after polishing. For the compression test, two-way ANOVA and Tukey post-test were used. For the other test, the Student’s t test was applied. The surface roughness decreased significantly after polishing (P <0.001), while residual stress (P = 0.722) and hardness (P = 0.782) were statistically similar for both materials. The size of the incisal reduction had a significant effect on fracture load (P = 0.020). Cracks imperceptible to visual inspection can be viewed when observed under optical microscopy. Residual stress and hardness were similar for SZ and FE. Polishing decreases the surface roughness of ceramics and can increase the size of the cracks. The incisal reduction in the preparation (1 mm and 4 mm) for ceramic veneers presented different fracture resistance values, and smaller incisal reductions reached higher fracture load values.