Photoelastic stress analysis of various post and core materials

Abstract

Core materials may enhance or exacerbate stress concentration around post systems. This study involved a photoelastic stress analysis of five different pre-fabricated post systems (Flexi-Post, E.D. S. ; Flexi-Flange, E.D. S. ; Dentatus Classic Post, Dentatus; Parapost, Coltene Whaledent; and V-lock Post, Brasseler;) in combination with three core materials (amalgam, composite, and Ti-core,E.D.S.;) Photoelastic material (PL-4M, Vishay Measurements Group) was cut into blocks 8×2.8×1.4 cm and the surfaces were polished to eliminate any residual stress due to the cutting procedure. Post-holes were drilled under water coolant on each block by using the corresponding drills from each post system. Zinc phosphate cement was used to cement the posts into the prepared post spaces. A core build up was fabricated over each post using an aluminum matrix and three different core materials; 1). amalgam, Diapersalloy (Caulk Dentsply) 2). Ti-Core (E.D. S.) and 3). composite, Encore (Centrix). Specimens were loaded with a probe connected to an Instron Universal Testing machine. Loads were 80 N in a vertical direction and 55 N at a 30(0) angle. Photographs were taken before and after loading for each sample under polarized light. Comparison of the stress distribution revealed that under vertical loading there was no difference in stress patterns generated around the various posts. With the load applied at 30(0) a difference in stress patterns was observed. The Dentatus classic Post and the V-lock Post generated less stress in the photoelastic medium than the other systems tested. The three core materials showed similar stress patterns with Dentatus posts and V-lock posts. Amalgam core with Parapost, Flexi-Post and Flexi-Flanges produced less stress than the other two core materials. The study suggests that the core material as well as the post system can be factor in stress distribution.