QUALITATIVE ASSESSMENT OF STRESS-DISTRIBUTION DURING INSERTION OF ENDODONTIC POSTS IN PHOTOELASTIC MATERIAL

Objectives: The purpose of this study was to investigate the stress pa tterns associated with prefabricated endodontic posts during the vario us stages of insertion according to a number of design characteristics . Methods: In a photoelastic material with elastic properties comparab le to dentin, analyses were performed of the overall stress patterns w ith polarized light revealing substantial differences in stresses gene rated by the various posts. The effects of variations in design for ce rtain configurations of the posts were also assessed. Results: One geo metric feature was the retentive thread of the post. The stress patter ns within the photoelastic material revealed a homogeneous distributio n of stress along the entire length of the thread, and more threads in duced additional stress, The stress recorded with a vent when the pitc h of the thread was 0.8-1.0 mm was classified as minimal-to-mild stres s. Another geometric feature considered was the head (coronal extensio n) 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 mm(2). Conclusions: This study suggests that during insertion of threaded posts the least stress occurs when the he ad contact surface is sufficient (greater than or equal to 3 mm(2)). A thread with a pitch of 0.8-1.0 mm is most desirable in stress reducti on. The number of windings should also be limited (less than six windi ngs) as samples with a substantial number of windings (N=13 or 30) pro duce severe stress. (C) 1998 Elsevier Science Ltd. All rights reserved .