Avaliação das propriedades ópticas de cor e translucidez do dissilicato de lítio CAD/CAM após ciclos de queimas

Abstract

Objective: To evaluate the optical properties of color and translucency after firing cycles and the application of glaze paste to 3 variations of CAD lithium disilicate. Material and methods. 180 rectangular CAD lithium disilicate specimens (5 x 6 x 1 mm) with a thickness of 1.0 ± 0.1 mm were obtained and divided into 18 subgroups according to the manufacturer's variations (HT, MT, LT), the number of firings they underwent and whether they received glase paste. Study I (n=90) evaluated the specimens after firing cycles without the application of glase paste. Study II (n=180) compared specimens with and without the application of glase paste after firing cycles. Each subgroup of n=10 was classified according to the number of firings they had undergone (1, 2 or 5 firings). The color parameters of the Cie*Lab system were measured for each subgroup superimposed on a black and white background. The data was applied to mathematical formulas to obtain ΔE/ ΔE00 and ΔTP/ ΔTP00. Analysis of variance (ANOVA) and Tukey's test were used for statistical analysis. The results were determined at a significance level of 95%(p<0.05). The specimens were analyzed using scanning electron microscopy (SEM) and electron dispersion spectroscopy (EDS). Results. Statistically significant differences were found in the *L, *a and *b parameters for HT, MT and LT in all firing periods. Comparing the subgroups in terms of color (ΔE), the highest ΔE values were found in HTNG5x (ΔE=3.7/ΔE00=3.0), followed by HTNG1x for black background and the lowest in LTGZ2x (ΔE=0.6/ΔE00=0.4). Comparing the differences between specimens with and without glase in terms of the number of firings, the subgroup with the greatest variations was MT with 1 firing (ΔE=8.1/ΔE00=5.9) and HT with 2 burns (ΔE=3.5/ΔE00=3.5). The ΔE values of all the subgroups with glase showed values above the perceptibility threshold, except for MTGZ5x (ΔE=0.4 and ΔE00= 0.3) and LTGZ2x (ΔE=0.6 and ΔE00= 0.4). When comparing ΔPT translucency, the lowest average values were found in MTGZ2x (ΔPT/ΔPT00= -0.2) and LTGZ2x (ΔPT=0.2/ΔPT00= 0.4). Except for the specimens with glaze after 2 firings (HTGZ2x, MTGZ2x, LTGZ2x) all the other subgroups had variations in translucency above the perception limit (ΔPT=1.33ΔPT00= 0.62) but still within the acceptance limit. Conclusions: The results showed that the color and translucency parameters of CAD lithium disilicate were affected by both the glase paste and repeated firings. For specimens that underwent up to two firings, the LT group showed the least variation in color, followed by the MT group. The HT group showed the greatest variation after multiple firings; therefore, its use should be preceded by additional caution because its color and translucency show a significant change after repeated firings.