ABSTRACT
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 metalceramic 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 [alpha=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