Comparison of the torsional forces at failure for seven endodontic post systems

Resistance to torsional forces is critical in restoration of endodontically treated teeth. Seven post designs (Flexi-Post, Flexi-Flange, Para-Post, AccessPost, World Post, Vlock, and Dentatus posts) were cemented in roots of natural teeth with zinc phosphate and Flexi-Flow cements, which resulted in 11 different groupings that were subjected to torsional forces in a clockwise direction. In addition, clockwise and counterclockwise torque was applied to the Flexi-Post and Flexi-Flange systems cemented with zinc phosphate and Flexi-Flow cements. A total of 150 samples were prepared, and groups for this study were: group 1, Flexi-Post/zinc phosphate clockwise and counterclockwise; group 2, Flexi-Post/Flexi-Flow clockwise and counterclockwise; group 3, Flexi-Flange/zinc phosphate clockwise and counterclockwise; group 4, Flexi-Flange/Flexi-Flow clockwise and counterclockwise; group 5, Para-Post/zinc phosphate clockwise; group 6, AccessPost/zinc phosphate clockwise; group 7, AccessPost/Flexi-Flow with grooved dentin clockwise; group 8, World Post/zinc phosphate clockwise; group 9, World Post/Flexi-Flow with grooved dentin clockwise; group 10, Vlock Post/zinc phosphate clockwise; and group 11, Dentatus post/zinc phosphate clockwise. Torsional forces for the groups ranged from 17 ounce-inches (Dentatus/zinc phosphate) to 81 ounce-inches (Flexi-Post/zinc phosphate). Flexi-Post and Flexi-Flange threaded posts exhibited statistically greater resistance to torsional forces. Analyses were computed with one-way and three-way analysis of variance followed by Duncan's multiple range test. Duncan's multiple range test indicated that Flexi-Post/zinc phosphate/clockwise was similar to Flexi-Post/Flexi-Flow/clockwise and that both had significantly higher torque levels than the other treatment conditions in the clockwise direction (p 0.0001). Dentatus/zinc phosphate/clockwise had significantly lower torque levels than the other treatment conditions (p 0.031).