Impact of multiple firings on thermal properties and bond strength of veneered zirconia restorations

OBJECTIVES This investigation evaluated the impact of multiple firings during the veneering process of all-ceramic restorations on the thermal properties and bond strength between veneering ceramics and zirconia. METHODS For the measurements of the coefficient of thermal expansion (CTE) prismatic specimens of four different veneering ceramics (ZRT/ZRO/HFZ/STR; N��=��40/n��=��10 per veneering ceramic) and rod-shaped zirconia specimens (N��=��2) were produced. 2 specimens of each veneering ceramic were fired 2, 4, 6, 8, and 10 times simulating dentine-firing. Measurements were performed in a dilatometer and glass transition temperature (Tg) was determined graphically. To analyze bond strength (BS), crack initiation test specimens were prepared using the same veneering ceramics and zirconia (N��=��600/n��=��150 per veneering ceramic). 30 specimens of each veneering ceramic were fired 2, 4, 6, 8, and 10 times. Half of them were thermocycled (5000 cycles, 5����C/55����C, 20s). The crack initiation test was conducted in a universal testing machine. Data was analyzed using ANOVA with partial eta squared statistics and post-hoc Scheff�� test as well as Pearson correlation test. RESULTS CTE was mostly affected by the choice of veneering ceramic (p��