Effect of thickness, processing technique and cooling rate protocol on the μTBS of a bilayer ceramic system

Purpose: To evaluate the influence of different processing techniques, ceramic thicknesses, and cooling rate protocols on the μTBS of a veneering ceramic to zirconia (Y-TZP). Materials and Methods: Eighty Y-TZP ceramic blocks (VITA In-Ceram 2000) with dimensions of 10 x 7 x 5 mm were obtained. The blocks were sintered in a special furnace at 1500° for 2 h, wet ground, and divided into 8 groups according to the factors processing technique (P: pressed/veneering ceramic PM9; or V: layered/ veneering ceramic VM9), thickness (2 mm and 4 mm), and cooling protocol (S: slow [10°C/s]; F: fast [50°C/s]). The Y-TZP/veneering ceramic blocks were sectioned to produce non-trimmed bar specimens (bonded area: 1 ± 0.1 mm2), which were submitted to 1200 thermal cycles (5°C and 55°C, 30-s dwell time) and stored for 1 week in distilled water (37°C) before microtensile testing in a universal test machine (EMIC, 1 mm/min). The data in MPa were analyzed statistically using three-way ANOVA and Tukey's test. Results: ANOVA revealed that only the factor processing technique was significant (p = 0.015), unlike the factors thickness (p = 0.111) and cooling protocol (p = 0.202). The majority of the failures were classified as adhesive. Conclusion: Layered application of a thin veneering ceramic using a fast cooling rate resulted in improved bonding between veneering ceramic and zirconia.