Photoelastic stress analysis of cast-gold endodontic posts

Two-dimensional photoelasticity was used to compare stresses generated upon loading of cast gold endodontic posts of two different diameters. Ten models were used, five for each diameter size tested. The models were constructed to simulate maxillary central incisors. Drill bits were used to prepare the root canal, and after root canal preparation was completed the post preparations were constructed using the Parapost system. The gold posts, made of type III gold, were cast using the Beauty Cast technique. A composite core was then placed on each of the posts to be tested. These models were positioned in a circular polariscope and vertical loads of 30 and 60 pounds were applied to each of the models, with the fringe patterns photographed immediately after each load was applied. The stresses were evaluated by determining the maximum fringe order in the simulated root and periodontium of the model. The results of this study suggest that (1) the diameter of a post with a core affects the magnitude of stress, (2) stress generally increases as post diameter increases, and (3) stress increases as the vertical load increases. It seems advisable to restrict the diameter of the post used in providing support for restorations, particularly when large occlusal for forces are exerted by the patient. The use of smaller diameter posts reduces the stresses exerted upon the dentin of the tooth and the tooth supporting structures, limits the amount of tooth material removed during preparation and, possibly, aids operative procedures by limiting the amount of tooth preparation.