In Vitro Analysis of the Fracture Resistance of Cad-Cam Cerasmart Molar Crowns with Different Occlusal Thickness

Abstract

Purpose: To compare the fracture resistance and mode of failure of CAD-CAM monolithic hybrid composite-nanoceramic crowns with different occlusal thickness. Materials and Methods:Thirty CAD-CAM monolithic hybrid composite-nanoceramic crowns with different occlusal thickness were randomly distributed into 3 groups: 0.5 mm, 1.0 mm and 1.5 mm.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. Results:The strength of the specimens progressively increased with occlusal thickness; the highest resistance to fracture was reported in 1.5 mm-thick crowns but no statistically significant differences were noticed among the experimental groups (p>0.05).The ultrathin crowns (0.5 mm) were mainly interested by unrestorable fractures. Conclusion:The occlusal thickness of CAD-CAM monolithic crowns did not influence the fracture resistance of restorations but it significantly affected their mode of failure; the occlusal thickness of such restorations can be reduced up to a lower bound of 1.0 mm in order to keep sufficient strength to with stand occlusal loads; CAD-CAM monolithic hybrid composite-nanoceramic crowns showed sufficient fracture resistance to be used in molar regions but not in an ultrathin configuration (0.5 mm).