Apparent fracture toughness of all-ceramic crown systems

This study measured apparent fracture toughness (Kc) and elastic modulus-to-hardness ratio (E/H) of dental restorations made with five all-ceramic crown systems. An indentation technique was used whereby Kc was calculated from the length of radial cracks formed on the release of a Vickers Diamond. Twenty-four crowns were made by using five different crown systems: Cerestore, DICOR, Hi-Ceram, Renaissance, and Vitadur-N. After the crowns were fired and glazed, they were embedded, polished, gold-coated, and indented under oil. In addition Knoop indentations were made for E/H calculation. Cerestore had a mean Kc of 1.79 MPa.m1/2 and E/H of 13.9, DICOR 2.10 and 26.8, Hi-Ceram 1.96 and 17.8, Renaissance 2.02 and 24.2, and Vitadur-N 1.96 and 22.3. Statistically significant differences (p less than 0.05) were found between DICOR and Cerestore materials for Kc and between DICOR, Renaissance, and Cerestore materials for E/H. For comparison, previous work found Vita VMK metal ceramic crowns to have a mean Kc of 1.91 MPa.m1/2 and E/H of 20.2.