Elastic modulus of posts and the risk of root fracture

The definition of an optimal elastic modulus for a post is controversial. This work hypothesized that the influence of the posts' elastic modulus on dentin stress concentration is dependent on the load direction. The objective was to evaluate, using finite element analysis, the maximum principal stress (σ_max) on the root, using posts with different elastic modulus submitted to different loading directions. Nine 3D models were built, representing the dentin root, gutta-percha, a conical post and the cortical bone. The softwares used were: MSC.PATRAN2005r2 (preprocessing) and MSC.Marc2005r2 (processing). Load of 100 N was applied, varying the directions (0°, 45° and 90°) in relation to the post's long axis. The magnitude and direction of the σ_max were recorded. At the 45° and 90° loading, the highest values of σ_max were recorded for the lowest modulus posts, on the cervical region, with a direction that suggests debonding of the post. For the 0° loading, the highest values of σ_max were recorded for higher modulus posts, on the apical region, and the circumferential direction suggests vertical root fracture. The hypothesis was accepted: the effect of the elastic modulus on the magnitude and direction of the σ_max generated on the root was dependent on the loading direction.