Influence of veneering technique and veneer-coping thickness on fracture toughness of implant retained veneered Y-TZP zirconia crowns

The aim of the study is to investigate the influence of veneering technique and veneer-coping thickness on the fracture toughness of implant retained zirconia crowns. Eighty zirconia copings are fabricated, half of which have 0.5 mm and the other half 1 mm thickness. Each 0.5 mm and 1 mm thickness coping is veneered to overall thickness of 3 and 4 mm using layering and hot press methods. Metal ceramic crowns with veneer-coping thickness of 2.5/0.5 mm are used as controls. All specimens are cemented to implant abutments using zinc oxide eugenol cement and tested using a micro-indenter. Crack lengths for specimens are evaluated to calculate fracture toughness using a formula. Results are analyzed using ANOVA. Veneer-coping thickness of 2.5/0.5 (5:1) and 3.5/0.5 (7:1) show significantly better (p = 0.001) fracture toughness as compared to V/C thickness of 2/1 (2:1) and 3/1 (3:1) for implant retained zirconia crowns. Metal ceramic crowns show significantly higher fracture toughness (p = 0.01) as compared to zirconia crowns of similar veneer/coping thickness. Veneering technique did not influence fracture toughness of zirconia crowns and hot-pressing is a viable technique for veneering Zr copings. Higher veneer-coping ratios i.e. thicker veneer and thinner copings, of zirconia crowns demonstrate better fracture toughness.