Effect of repeated firing on the translucency of CAD-CAM monolithic glass-ceramics

• Published in: The Journal of prosthetic dentistry Vol. 123; no. 3; pp. 530.e1 - 530.e6
• Main Authors: Nejatidanesh, Farahnaz, Azadbakht, Kamran, Savabi, Omid, Sharifi, Morteza, Shirani, Mohammadjavad
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.03.2020
• Subjects: Ceramics; Color; Computer-Aided Design; Dental Porcelain; Dentistry; Materials Testing; Surface Properties; Zirconium
• ISSN: 0022-3913; 1097-6841
• DOI: 10.1016/j.prosdent.2019.10.028

The effects of multiple firings on the translucency of newly introduced computer-aided design and computer-aided manufacturing (CAD-CAM) glass-ceramics have not been well evaluated. The purpose of this in vitro study was to assess the changes in the translucency of high-translucency (HT) and low-translucency (LT) lithium disilicate (LDS) and zirconia-reinforced lithium silicate (ZLS) glass-ceramics of 0.6 and 1 mm thickness during crystallization, correction, and glaze firing cycles. Eighty specimens in 8 groups (n=10) were sectioned and polished to obtain thicknesses of 0.6 and 1 mm. The specimens were then fired in 3 cycles, and the color coordinates were measured by using a spectrophotometer after each cycle. The translucency parameter (TP) and the contrast ratio (CR) were calculated to determine the translucency level. The data were analyzed by using a statistical software program. The TP and CR data after each firing cycle were compared within each group by using repeated-measures ANOVA. Pair-wise comparisons were made by using a multiple paired t test. Comparisons between the 2 thicknesses of different materials were made by using the independent t test (α=.05). Repeated firings significantly increased the translucency of 0.6-mm LT-LDS and decreased the translucency of 0.6-mm HT-ZLS (P<.017). No significant changes were noted in the translucency of specimens of 1-mm thickness after repeated firings. Also, 0.6-mm-thick specimens of all materials had significantly higher translucency than 1-mm-thick specimens (P≤.001). The highest translucency was noted in HT-LDS, followed by HT-ZLS. Repeated firings significantly affected the translucency of LDS and ZLS CAD-CAM glass-ceramics. The translucency increased with decreasing thickness.