Damage morphology produced in low-cycle high-load indentations of feldspar porcelain and leucite glass ceramic

This paper reports on damage morphology created in low-cycle high-load spherical indentations of feldspar porcelain and leucite glass ceramic to mimic teeth clenching or grinding. Maximum contact stresses were evaluated as functions of cycle numbers and applied loads using a Hertz model. The surface damage of the two materials after low-cycle high-load indentation testing was viewed using scanning electron microscopy to understand the relations between crack propagation and microstructures. The results indicate that the maximum contact stresses for both materials reduced significantly with the cycles (ANOVA, p < 0.05) but did not show a significant change with the applied loads (ANOVA, p > 0.05). Feldspar porcelain can endure much less maximum contact stress than leucite glass ceramic. Low-cycle high-load spherical indentations induced extensive ring cracks, wedging of crack faces by debris, fragmentation, and pulverization on feldspar porcelain surfaces. In contrast, leucite glass ceramic surfaces yielded only minimum microcracks at 500 N load and localized fractures and cracks at the higher loads of 600 and 700 N. This study shows that leucite glass ceramic had much higher resistance to low-cycle high-load fatigue impacts than feldspar porcelain and it can be a better choice for restorations under teeth clenching and grinding conditions