Fracture resistance of implant metal-ceramic single restorations

The purpose of this work was to compare the porcelain fracture resistance of screw-retained, cement-retained, and the combined screw- and cement-retained MC implant crowns. Fifty standardized MC molar-shaped crowns were fabricated. The 50 crowns were divided into five groups (SRC, SRO, CRP, CRE and CSC. Group SRC: screw-retained with the screw-access hole placed in the centre of the occlusal surface; Group SRO: screw-retained with the screw access hole placed 1 mm offset from the centre of the occlusal surface; Group CRP: cement-retained with zinc phosphate; Group CRE: cement-retained with zinc oxide eugenol; Group CSC: cement-retained with a screw-access hole in the centre of the occlusal surface, zinc phosphate cement was used. All test specimens were thermocycled and vertically loaded in a universal testing machine at a crosshead speed of 2 mm/min until fracture. Conclusion: The cementretained restorations showed significantly higher mean fracture loads than the restorations having a screw-access hole. The position of the screw-access hole or the type of cement did not significantly affect the porcelain fracture resistance.