the influence of composite thickness with or without fibers on fracture resistance of direct restorations in endodontically treated teeth

introduction: this in vitro study evaluated the influence of composite thickness (with or without fiber reinforcement) on fracture resistance of direct restorations in endodontically treated teeth. methods and materials: fifty-six intact human premolars were chosen and randomly divided into four groups ( n =14). after preparation of a mesio-occluso-distal (mod) cavities and cusp reduction, the teeth were endodontically treated. subsequently, the samples were restored with composite resin using the following protocols: group 1 ; composite onlay with cusp coverage of 1.5 mm, group 2 ; composite onlay with cusp coverage of 2.5 mm, group 3; composite onlay (including resin-impregnated fiber) with cusp coverage of 1.5 mm and group 4; composite onlay (including resin-impregnated fiber) with cusp coverage of 2.5 mm. the fracture resistance of teeth in all test groups was calculated by subjecting them to a progressively increasing compressive axial force in the universal testing machine with the cross-head speed of 1 mm/min to the point of fracture. the data were analyzed using the kruskal-wallis test. results: the mean fracture strengths and obtained standard error were 1263.85±74.03 n, 1330.26±128.01 n, 1344.92±64.40 n and 1312.54±75.63 n for groups 1 to 4, respectively. statistical analysis revealed no significant difference between groups. conclusion: cusp coverage of 1.5 and 2.5 mm in mod access cavities with or without insertion of resin impregnated fiber had similar fracture rates in the endodontically treated teeth.