Qualitative assessment of stress distribution during insertion of endodontic posts in photoelastic material

Objectives: The purpose of this study was to investigate the stress patterns associated with prefabricated endodontic posts during the various stages of insertion according to a number of design characteristics. Methods: In a photoelastic material with elastic properties comparable to dentin, analyses were performed of the overall stress patterns with polarized light revealing substantial differences in stresses generated by the various posts. The effects of variations in design for certain configurations of the posts were also assessed. Results: One geometric feature was the retentive thread of the post. The stress patterns within the photoelastic material revealed a homogeneous distribution of stress along the entire length of the thread, and more threads induced additional stress. The stress recorded with a vent when the pitch of the thread was 0.8–1.0 mm was classified as minimal-to-mild stress. Another geometric feature considered was the head (coronal extension) of the post. Minimal stress was recorded in the material in contact with the head and the apical end of the post when the contact surface of head was more than 3 mm2. Conclusions: This study suggests that during insertion of threaded posts the least stress occurs when the head contact surface is sufficient (greater-or-equal, slanted3 mm2). A thread with a pitch of 0.8–1.0 mm is most desirable in stress reduction. The number of windings should also be limited (less than six windings) as samples with a substantial number of windings (N=13 or 30) produce severe stress.