Influence of Microstructure and Chemistry on the Fracture Toughness of Dental Ceramics
Janet Quinn, Veeraraghavan Sundar, Isabel K. Lloyd
Objectives: The primary aim of this research was to measure fracture toughness for several groups of dental ceramics, and determine how this property is affected by chemistry and microstructure.Methods: Fracture toughness (KIc) values were obtained using Single Edge Precracked Beam (SEPB) and Single Edge V-Notch Beam (SEVB) methods. Dynamic Young's modulus, which often scales with strength and has been used in explaining the microstructure/toughness relationship on a theoretical basis, was also obtained for the three groups of materials comprising this study. The first group, consisting of micaceous glass ceramics, varied systematically in microstructure but not in chemistry. The second group, the leucite porcelains, varied significantly in microstructure, but little in chemistry. The ceramics comprising the third group were significantly different in both chemistry and microstructure. Results: Upper toughness limits for the micaceous glass-ceramics and leucite porcelains were significantly raised compared to the base glasses, but remained under 2 MPa-m1/2. The highest toughnesses were associated with high percent crystallinity, large grains and high aspect ratios. The third group KIc values were 2.8 MPa-m1/2 for a lithium disilicate glass-ceramic, 3.1 MPa-m1/2 for a glass-infused alumina, and 4.9 MPa-m1/2 for zirconia.