Efeitos do número de camadas de glazeamento na estabilidade de cor e propriedades mecânicas de uma cerâmica vítrea de dissilicato de lítio CAD-CAM caracterizada extrinsecamente submetida à escovação e à termociclagem

Abstract

The use of extrinsically characterized monolithic CAD-CAM ceramic restorations has been widely indicated, due to their faster fabrication and their good esthetic and biomechanical results. However, little is known about the stability of these results over the years and the effects of different glaze layers on their preservation are unknown. The aim of this study was to evaluate the effects of the number of glaze layers on a CAD- CAM lithium disilicate glass ceramic extrinsically characterized, in terms of color properties, surface roughness and Vickers microhardness, after thermocycling (TC), brushing (E ) and association of both (TCE). The specimens (n=80) were divided into 2 groups (n=40): glazed with one layer (GL1); glazed with two layers (GL2). Each group was subdivided into four (n=10), for 3 types of interventions and 1 control (TC, E, TCE and immersion in distilled water), and measurements were taken at 4 different times (baseline; 2.5; 5; and 10 years). Color variations were evaluated using a spectrophotometer and applying the formula CIEDE2000 (ΔE00). A contact profilometer was used to measure the surface roughness (Ra) and a Vickers microhardness meter for the microhardness (MD). Mixed 3-way ANOVA was used for all outcomes, followed by 1-way ANOVA, 1-way repeated measures ANOVA, Bonferroni post-test and t test to check for differences (α=0.05). The GL1 group suffered greater color change with E from 5 years on (p=0.003). At 2.5 years and 5 years, TC generated greater color changes whencompared to control (p<0.001; p=0.013). The GL2 group suffered greater color changes in E for 10 years (p=0.017). Regarding Ra, in 5 years, the GL1 group suffered alterations in TCE. In the control, it was verified that the GL1 group was rougher than the GL2 (p<0.05), however the Ra was equal in the TCE at all times and in the TC in 10 years. All groups experienced an increase in MD at 2.5 years (p<0.05), with the exception of the GL1 group that underwent E. In the GL1 group, TC increased the MD at 5 years, compared to the control (p=0.006); at 5 and 10 years, the GL1 group presented higher MD than the GL2 in TCE (p<0.05). In conclusion, in general, one layer of glaze showed greater changes in color, roughness and microhardness, compared to those made with two layers.