Effect of citric acid on color stability and surface roughness of translucent monolithic zirconia with different staining techniques

Abstract

Background and rationale: Translucent monolithic zirconia is developed to solve the problem of esthetic in the conventional generation of zirconia with high opacity. When these materials are used for anterior restoration in the oral cavity, they can contact with foods and beverages that are acidic, which may affect the color stability and surface roughness of the material at different levels.

Objective: The objective of this study was to determine the effects of citric acid on color stability and surface roughness of translucent monolithic zirconia with different staining techniques.

Materials and Methods: A total of 80 disc specimens of VITA YZ® XT (14 mm in diameter and 1.5 mm in thickness) were designed with computer-aided design and computer-aided manufacturing (CAD-CAM) software then cut with a low-speed saw and sintered, according to the manufacturer's instruction. All sintered specimens were divided into 4 groups, including no treatment (NT), polishing (PO), stained then glazed (S-G) and mixing of stain and glaze (S+G). For the PO specimens, they were polished by diamond coated grinding bur and VITA SUPRINITY® polishing set. The S-G and S+G groups were subjected to glaze coated by VITA AKZENT Plus® STAIN and GLAZE. All specimens were separated into 2 subgroups (n=10). The first subgroup was immersed in artificial saliva at 37 °C for 14 days to simulate the exposure of saliva in the oral cavity for 2 years in vivo. It was also used as a control group. The other subgroup was immersed in 2% citric acid solution for 8 h to simulate 2-year exposure of citric acid in the oral cavity. The measurement of color change (∆E) and surface roughness (Ra) before and after the immersion was conducted with a spectrophotometer and a contact type profilometer respectively.

Results: For the color change, the results showed that S+G and S-G groups had significantly higher mean values of ∆E than NT and PO groups in both solutions. When considering these 2 staining techniques, ∆E value in citric acid solution was significantly higher than artificial saliva. However, no significant difference of ∆E was observed between S+G and S-G groups. For the surface roughness, there was no statistically significant difference between surface roughness (Ra) and surface roughness change (∆Ra) among 4 surface finish groups in both solutions.

Conclusions: It can be concluded that citric acid had an unfavorable effect on the color stability of both staining techniques on translucent monolithic zirconia but did not exceed the perceptible threshold. However, citric acid did not affect the surface roughness in all surface finish groups.