the effects of new design of access hole on porcelain fracture resistance of implant-supported crowns

statement of the problem: one disadvantage of cement-retained crowns is the lack of predictable irretrievability. this problem can be overcome through designing a screw access hole in the metal substructure of cement-retained restoration and using porcelain stain to define this area. purpose: this study aimed to evaluate the influence of existence of screw access hole on porcelain fracture resistance of metal-ceramic implant-supported crowns. materials and method: thirty six standardized metal-ceramic crowns were fabricated and divided into 3 groups (n=12); group 1 conventional cement-retained metal-ceramic crowns as control group, group 2 cement-retained mc crowns in which porcelain stain was used to define the location of screw access channel, and group 3 cement-retained metal-ceramic crowns in the metal substructure of which a hole and ledge was designed in the location of screw access channel. the specimens were cemented (tempbond, kerr) to their dedicated abutments. a hole was made in the location of screw access channel in group 2 and 3 and filled with photo-polymerized composite resin (3m; espe). all specimens were thermocycled and loaded in universal testing machine at crosshead speed of 2mm/min until fracture. mean values of load at fracture were calculated in each group and compared with one-way anova (α=0.05). results: mean value of the load required to fracture the restorations was 1947±487 n in group 1, 1927±539 n in group 2, and 2170±738 n in group 3. no statistically significant difference was found between the fracture resistance values of the three groups ( p > 0.05) conclusion: presence of screw access channel in cement-retained implant restorations does not compromise fracture resistance.