Evaluation of the effect of corrosion on color stability of LDS and ZLS ceramics after glazing or mechanical polishing surface treatment
Abstract
Introduction: Similar to natural human teeth, dental ceramics are also affected by different bevarages in intraoral environment, which can lead to color changes. The effect of surface corrosion on the color stability of dental ceramics is still not fully known. The aim of this study is to determine the effect of corrosion on the color stability of CAD/CAM ceramic restorations of Lithium Disilicate and Lithium Silicate reinforced with Zirconia after applying two methods of surface treatment, glaze or mechanical polishing, following 2-weeks storage in coffee solution.
Materials and methods: In this experimental study, 88 rectangular samples with dimensions of 1.5x7x12 mm were prepared from two types of ceramic blocks LDS (n=44), ZLS (n=44) in A2 color
ZLS (Zirconia-reinforced lithium silicate) (Celtra Duo, Dentsply)
LDS (Lithium Disilicate glass-ceramic) (IPS e.max CAD, Ivoclar Vivadent AG)
The prepared samples were placed in an ultrasonic device to remove residual particles and surface pollution. Then, samples were sintered and completely crystallized by porcelain furnace and according to ZLS factory instructions for 8 minutes at 840 degrees Celsius and LDS for 10 minutes at 850 degrees Celsius. To standardize the process and homogenize the surface of the samples before work, all the samples were polished with a low-speed handpiece and water cooling, by silicon carbide sandpaper, by one person for 60 seconds for each sample, and then the samples were placed in an ultrasonic device containing distilled water for 10 minutes, and then completely dried with poar and the samples of each type of ceramic were randomly divided into two equal groups to apply glaze or polishing surface treatment. The samples of group one (LDS polish) and group three (ZLS polish) were polished by a polishing kit, and the samples of group two (LDS glaze) and group four (ZLS glaze) were glazed in the furnace. Then each group of samples was divided into two equal groups A and B after washing with Ethanol 3 times and drying. Group A samples were immersed in 40% acetic acid solution for 16 hours at a temperature of 80 degrees in order to create corrosion. Centigrade was cooled to ambient temperature and after washing with deionized water and then ethanol, they were dried, then all the samples (A, B) were immersed for 24 hours in distilled water at a temperature of 37 degrees Celsius .They were immersed in coffee as a coloring agent for two week before and after immersion, the color of the samples was quantitatively measured using a spectrophotometer, the color characteristics were measured by three parameters I, a, b and finally the value of E changed Color was compared. Independent t-test and non-parametric Mann-Whitney U test were used to investigate the effect of corrosion on the color stability of ceramics before and after immersion in coffee. Color changes after calculation were statistically analyzed using three-way ANOVA. A probability value of less than 0.05 was considered as a significant level. SPSS version 27 software was used for data analysis.
Results: The results of the pilot study of the current research showed that 4% acetic acid does not change the kerogen restorations, so we used a concentration of 40% to check the kerogen.
In the current study, in ZLS restoration, the amount of color change in mechanical polishing surface treatment (under kerogen: 1.71±0.42 and without kerogen: 1.03±0.28) and in glaze surface treatment method (under kerogen: 0.81±0.34 and without kerogen: 0.37±0.18) And also in LDS restoration, the amount of color change in the mechanical polishing surface treatment (under kerogen: 14.82 and without kerogen: 8.18) and in the glaze surface treatment method (under kerogen: 1.59±0.66 and without kerogen: 0.92±0.34), which indicates the type of ceramic block, The type of surface treatment, kerogen, are factors that each alone have a significant effect on the color change of ceramics.
Conclusion: All three factors that had been examined in the study; the type of restoration, the type of surface treatment, and surface corrosion have a significant effect on the color stability of CAD/CAM ceramics. In both types of Lithium Disilicate ceramics and lithium silicate reinforced with zirconia, the glaze process caused more color stability compared to the mechanical polishing process. Among the two types of ceramics; Lithium silicate reinforced with zirconia had more color stability compared to lithium di silicate ceramic. In both types of ceramics, the effect of surface treatment on ceramic color stability was more than the effect of ceramic type.