In vitro analysis of the fracture resistance of CAD CAM monolithic zirconia molar crowns with different occlusal thickness.
OBJECTIVES To compare the fracture resistance and mode of failure of CAD CAM monolithic zirconia crowns with different occlusal thickness. MATERIAL AND METHODS Forty CAD CAM monolithic zirconia crowns with different occlusal thickness were randomly distributed into 4 experimental groups: 2.0mm (group 1) 1.5mm (group 2) 1.0mm (group 3) and 0.5mm (group 4) The restorations were cemented onto human molars with a self adhesive resin cement. The specimens were loaded until fracture; the fracture resistance and mode of failure were recorded. The data were statistically analyzed with the one way ANOVA followed by the Fisher's Exact test with Bonferroni's correction (p=0.05) RESULTS The fracture resistance values of all the specimens exceeded the maximum physiological occlusal loads in molar regions. All the crowns showed cohesive microcracks of the zirconia core; only 1 crown with a thickness of 0.5mm was interested by a complete fracture. CONCLUSIONS The occlusal thickness of CAD CAM monolithic zirconia crowns did not influence either the fracture resistance and the mode of failure of the restorations; the occlusal thickness of CAD CAM monolithic zirconia crowns can be reduced up to a lower bound of 0.5mm keeping a sufficient strength to withstand occlusal loads; CAD CAM monolithic zirconia crowns showed sufficient fracture resistance to be used in molar regions, even in a thin configuration (0.5mm)
Journal of the mechanical behavior of biomedical materials