FRACTURE-TOUGHNESS AND FRACTOGRAPHY OF DENTAL CERAMICS

Chevron-notch short-rod fracture toughness (K(Iv)) and scanning electron microscopy analyses of leucite-, tetrasilicic fluormica-, and alumina- reinforced dental ceramics and control materials were investigated. Shortrod fracture toughness is a measure of the bulk resistance to crack propagation but not of the surface resistance to crack initiation. Results indicated significant differences in K(Iv) among the following six groups (from lowest to highest (a) Dicor and Optec, (b) Optec, Excelco's Incisal, Macor and Excelco's Gingival, (c) Excelco's Brush-O-Paque, (d) Vitadur-N core, (e) Corning's 9606 glass-ceramic, and (f) Vita Hi Ceram. Good agreement occurred with published data for Macor and 9606. Comparisons of K(Iv)'s to published bending properties revealed poor correlation with both Dicor and Optec. This was attributed to sample geometry and surface preparational differences between short-rod and bending samples. Fractography analysis revealed the brittle nature of the glassy matrix with all fractured surfaces. The alumina particles inhibited crack propagation by pinning the crack at the particle-matrix interface. The fluormica and leucite phases revealed a higher incidence for cleavage fracture. The opaque particles offered some reinforcement effect.