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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.
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    Mechanical properties of high- and low-fusing zirconia veneering ceramics fired on different trays and substrates
    (MDPI, 2024) Hoffmann, Moritz; Coldea, Andrea; Dönmez, Mustafa Borga; Meinen, John
    This study aimed to evaluate the effect of ceramic type, firing tray, and firing substrate on the density, shrinkage, biaxial flexural strength, Martens' hardness, and elastic indentation modulus of zirconia veneering ceramics. Disk-shaped specimens were fabricated from a high-fusing (HFZ) and a low-fusing (STR) zirconia veneering ceramic. These specimens were then divided into 10 groups according to firing trays (round, small honeycomb-shaped, cordierite [RSC]; round, large honeycomb-shaped, aluminum oxide [RLA]; rectangular, plane, silicon nitride [RCPS]; round, plane, silicon nitride [RPS]; and rectangular, plane, calcium silicate [RCPC]) and firing substrates (firing cotton and platinum foil) used (n = 12). The density, shrinkage, biaxial flexural strength, Martens' hardness, and indentation modulus were measured, and analyzed with generalized linear model analysis (alpha = 0.05). The interaction between the ceramic type and firing substrate affected density (p < 0.001), and the other outcomes were affected by the interaction among all main factors (p <= 0.045). Higher density was observed with HFZ or platinum foil (p <= 0.007). RSC and RLA led to a higher density than RCPS within HFZ and led to the lowest density within STR (p <= 0.046). STR had a higher shrinkage (p < 0.001). RSC mostly led to a lower shrinkage of HFZ (p <= 0.045). The effect of ceramic type and firing substrates on the biaxial flexural strength, Martens' hardness, and indentation modulus was minimal while there was no clear trend on the effect of firing tray on these properties. Ceramic type, firing tray, and firing substrate affected the mechanical properties of the tested zirconia veneering ceramics. Firing the tested zirconia veneering ceramics over a round and small honeycomb-shaped cordierite firing tray with firing cotton mostly led to improved mechanical properties.