Fracture Toughness (KIC) of a Hot-Pressed Core Ceramic Based on Fractographic Analysis of Fractured Ceramic FPDs

Purpose: The objective of this study was to test the hypothesis that there is no significant difference between the fracture toughness (KIC) of an experimental hot-pressed core ceramic measured by fractographic analysis of failed ceramic prostheses and the values determined by other standard methods. Materials and Methods: Four groups were subjected to one of four test methods: group 1 = indentation strength technique (standard numerical calculation); group 2 = indentation strength technique (fractographic analysis); group 3 = flexure test of precracked specimens (fractographic analysis); and group 4 = fractographic analysis of failed three-unit fixed partial dentures (FPD). For groups 1 to 3, 20 ceramic bar specimens were subjected to three-point flexure at a cross-head speed of 0.5 mm/min until fracture occurred. For group 4, 10 failed FPDs were collected from a previous study. Stress values at failure were calculated from either a flexure stress equation (groups 1 to 3) or from finite element analyses (group 4). KIC values were calculated from an equation and fractographic measurement data. Results: Mean fracture toughness ranged from 3.1 MPa·m1/2 (SD 0.2) (group 1) to 3.4 MPa·m1/2 (SD 0.2) (group 4). The mean KIC value for group 1 was significantly different from that of group 4; however, no significant differences were found between groups 1, 2, and 3, or between groups 2, 3, and 4. Conclusion: Fracture toughness for an experimental hot-pressed core ceramic measured by fractographic analysis in combination with finite element analysis was comparable with the values determined with other standard fractographic methods.