Quantitative Photoelastic Analysis of the Stress Distribution around Four Types of Endodontic Posts

Objective: To analyze the distribution and magnitude of the stresses created by insertion of endodontic posts into 2-dimension half-ellipse shaped photoelastic models of the roots of endodontically prepared crownless human upper central incisors. Methods: Five each of Carbon Fiber Posts (CF), Flexipost (FP), Parapost Plus (PP), and Parapost XT (XT), were seated in the prepared canals to a depth of 9 mm. All posts were cemented with zinc phosphate cement. The CF posts were also cemented with resin cement. Magnified fringe patterns created in the PSM-5 photoelastic resin (SOC = 228 fringe/MPa/mm) were photographed. Fringe patterns were plotted and stress magnitudes determined from fringe order color. Data were statistically evaluated by ANOVA & Newman-Kuels Test. Results: The passively engaging posts CF & PP showed no change in fringe pattern following post insertion. The actively engaging posts FP & XT showed fringe patterns indicative of stresses exceeding 1 MPa. Stresses occurred in the region of increased post diameter and were concentrated at the coronal root surfaces of FP and in the coronal half of the roots of XT. Conclusions: Cementing agent setting shrinkage does not introduce detectable stress; insertion of posts that actively engage create, as a result of engagement, small, statistically similar stresses whereas passive posts create none (P<0.0001); post geometry affects stress distribution. Supported by NSERC grant #203449-02.