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    Effect of final temperature and heating rate on the mechanical and optical properties of a zirconia veneering ceramic
    (Elsevier, 2024) Coldea, Andrea; Donmez, Mustafa Borga; Stawarczyk, Bogna
    Purpose: To evaluate the effect of firing temperature and heating rate on the volumetric shrinkage, translucency, flexural strength, hardness, and fracture toughness of a zirconia veneering ceramic.Material and methods: Zirconia veneering ceramic specimens (N = 45) with varying final temperatures (730 degrees C, 750 degrees C, and 770 degrees C) and heating rates (70 degrees C/min, 55 degrees C/min, and 40 degrees C/min) were fabricated (n = 5). Each specimen's shrinkage, translucency, flexural strength, hardness, and fracture toughness were determined. Two-way analysis of variance, Scheff & eacute; test, and Pearson's correlation analysis were used to evaluate data (alpha = 0.05).Results: The shrinkage (44.9 +/- 3.1-47.5 +/- 1.6 vol%) and flexural strength (74.1 +/- 17.4-107.0 +/- 27.1 MPa) were not affected by tested parameters (P >= 0.288). The interaction between the main factors affected the translucency, hardness, and fracture toughness of the specimens (P <= 0.007). Specimens with 770 degrees C final temperature and 70 degrees C/min heating rate had the lowest (21.8 +/- 3.2 %) translucency (P <= 0.039). The hardness ranged between 4.98 +/- 0.51 GPa (730 degrees C; 70 degrees C/min) and 5.60 +/- 0.37 GPa (770 degrees C; 70 degrees C/min). Fracture toughness ranged between 0.54 +/- 0.04 MPa root m and 0.67 +/- 0.08 MPa root m with the highest values for specimens fired at 730 degrees C with 70 degrees C/min (P <= 0.001). There was a positive correlation between translucency and hardness (r = 0.335, P = 0.012), and a negative correlation between fracture toughness and all parameters other than shrinkage (translucency: r = -0.693/P < 0.001, flexural strength: r = -0.258/P = 0.046, hardness: r = -0.457/P < 0.001).Conclusions: Heating rate and final temperature should be considered while fabricating veneered zirconia restorations with tested ceramic as they affected the translucency, hardness, and fracture toughness.