Comparison of the photoelastic stress properties for two combination prefabricated cast post systems

The reason for a post and core preparation is to provide an anchoring system for a final restoration to the tooth root. This experiment was divided into two groups with the following systems; ExactaCast and Parapost. Casts for these systems were fabricated in photoelastic plastic and cemented with zinc phosphate cement. These photoelastic blocks were placed in a special jig on a universal testing machine. The experiment compared the photoelastic stresses generated for these two systems in two different stress modes; vertically at 30 pounds and obliquely (at a 26 degree angle) at 20 and 30 pounds. Specimens were then photographed after cementation in the unloaded and loaded states. Minimal stresses were observed for the ExactaCast in the unloaded state, while symmetric, even patterns of stresses concentrated coronally were present in the loaded vertical and oblique states. Minimal stresses were observed for the Parapost in the unloaded state, while asymmetric, uneven patterns of stresses concentrated apically were present in the loaded vertical and oblique states. The presence of the multiple tiered system for the Exacta-Cast clearly directs stresses in a symmetric pattern, while the single tiered Parapost system directs stresses in asymmetrical pattern. The symmetric even stresses for the ExactaCast are more favorable than the asymmetric, uneven stresses for the Parapost.