Porcelain Fracture Resistance of Screw‐Retained,Cement‐Retained,and Screw‐Cement‐Retained Implant‐Supported Metal Ceramic Posterior Crowns

Purpose: The purpose of this in vitro study was to compare the porcelain fracture resistance between screw‐retained, cement‐retained, and combined screw‐ and cement‐retained metal–ceramic (MC) implant‐supported posterior single crowns; and to investigate the effect of offsetting the occlusal screw‐access opening on porcelain fracture resistance of screw‐retained and cement‐retained MC implant‐supported posterior single crowns. Materials and Methods: Forty standardized MC molar‐shaped restorations were fabricated. The 40 restorations were divided into four groups (SRC, SRO, CRP, and CSC) of 10 specimens each. Group SRC: screw‐retained, screw‐access hole placed in the center of the occlusal surface; Group SRO: screw‐retained, screw access hole placed 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group CRP: cement‐retained, zinc phosphate cement was used; Group CSC: cement‐retained with a screw‐access hole in the center of the occlusal surface. The screw‐retained restorations and abutments were directly attached to 3i implant fixtures embedded in acrylic resin blocks. Subsequently, all test specimens were thermocycled and vertically loaded in a universal testing machine at a crosshead speed of 2 mm/min until fracture. Mean values of load at fracture (in N) were calculated in each group and compared with a one‐way ANOVA and Tukey's Studentized test (α= 0.05). Results: Mean values of loads required to fracture the restorations were as follows (N): Group SRC: 1721 ± 593; Group SRO: 1885 ± 491; Group CRP: 3707 ± 1086; Group CSC: 1700 ± 526. Groups SRC, SRO, and CSC required a significantly lower force to fracture the porcelain than did the CRP group (p < 0.05). Conclusion: The cement‐retained restorations showed significantly higher mean fracture loads than the restorations having screw‐access openings in their occlusal surface. The position of the screw‐access hole within the occlusal surface did not significantly affect the porcelain fracture resistance.