Effect of thermocycling and khat extract staining on the optical and mechanical properties of ceramic materials

Background: Color stability of CAD/CAM prosthetic materials is important for long-term clinical and survival success during daily chewing habit. Aims: To assess the effects and outcome of thermocycling and khat extract (KE) staining on the optical (i.e., TP and OP) and physical properties of multilayer zirconia and feldspathic CAD/CAM ceramic. Methods: Forty specimens with dimensions of 16 mm x 12 mm x 1.8 mm were produced from multilayer zirconia and feldspathic CAD/CAM ceramic materials. Specimen's surfaces were prepared in glazed and polished forms. Before thermocycling, the color parameters of specimens were measured using a spectrophotometer, again and after the thermal aging process, the color measurement was recorded and analyzing the collected data using descriptive statistics, correlation, one-way ANOVA, and Tukey's tests. Results: After thermocycling and KE staining, the color parameters L, a, and b decreased, and Delta L*, Delta a* Delta b* had significant differences between groups (p values >= 0.050). Polished surfaces had higher TPs compared with glazed surfaces. OP values ranged from 22.1 to 16.2 and were higher in glazed than in polished surfaces. Glazed and polished zirconia (777.42 +/- 72.67N and 533 +/- 50.71 N) had significantly higher compressive fracture forces compared with glazed and polished Vita Triluxe (396.25 +/- 42.24N and 338.66 +/- 40.17N). Conclusion: KE staining and thermocycling caused slight color changes in TP and OP values, which were high in polished surfaces. TP and OP values were reduced after KE immersion and thermocycling. Compressive forces were under clinically accepted values for zirconia and less than half values for Vita Triluxe specimens. The three types of failures were presented.