Influência do tempo de condicionamento com ácido fluorídrico nas propriedades mecânicas de cerâmica à base de dissilicato de lítio para CAD/CAM

Abstract

The aim of the present study was to evaluate, in vitro, the influence of hydrofluoric acid etching time on the surface and the flexural strength of a CAD/CAM lithium disilicate-based glass ceramic. Pre-sintered lithium disilicate blocks were sectioned into bars (14 x 4 x 1mm). The specimens were polished, ultrasonically cleaned, crystallized and divided into 5 different groups (n = 15), according to the etching time: 0s (no etching), 20s, 40s, 60s and 120s. After conditioning, the surface roughness was assessed (μm), the contact angle measurement (°) were evaluated for wettability assessment and the three-point bending test for flexural strength (MPa) determination was conducted. Micromorphological analysis of the etched surfaces was conducted in a scanning electron microscope and atomic force microscope. The data were submitted to one-way ANOVA and post hoc Tukey’s test (α = 0.05). There was a statistical difference between the times tested for the variables evaluated (p = 0.001). The higher conditioning time (120s, p = 0.001) resulted in higher roughness value (0.51 μm), lower contact angle (19.23 °, p = 0.001) and lower flexural strength (324.23 MPa; = 0.001). Based on the findings of this study, it is possible to conclude that the increase of the etching time increased surface roughness for the 20s, 60s and 120s times, and reduced the contact angle in 40s and 120s, reducing the flexural strength in the time of 120s. The micrographs evidenced an increase in surface irregularities and depth of etching with the increase in the time of hydrofluoric acid action.