Elastic modulus of posts and the risk of root fracture

Abstract

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 (sigma(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 degrees, 45 degrees and 90 degrees) in relation to the post's long axis. The magnitude and direction of the sigma(max) were recorded. At the 45 degrees and 90 degrees loading, the highest values of sigma(max) were recorded for the lowest modulus posts, on the cervical region, with a direction that suggests debonding of the post. For the 0 degrees loading, the highest values of sigma(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 sigma(max) generated on the root was dependent on the loading direction.

Effect of root canal preparation, type of endodontic post and mechanical cycling on root fracture strength

“…This behavior is in agreement with Meira, et al. 21 (2009), who showed that a post with low elastic modulus, when under 45° oblique load, tends to bend with a fulcrum localized in the cervical third, opposite the load application 5 . Due to the post's low rigidity, the curvature is noticeable, which leads to larger post elongation at the side of the load application.…”

“…When the post and the dentin are perfectly bonded, a higher post deformation causes greater dentin deformation and, consequently, more stress. Hence, according to the stress concentration and its direction, a trend is found for post debonding, instead of irreparable root vertical fracture 21 . On the other hand, catastrophic failures were evidenced only in the groups which received a cast post and core, since the higher stress concentration occurs in the post and root apical third 11 .…”

Fracture Resistance of Teeth Restored with Post-retained Restorations: An Overview

“…Meira et al (182) found that the effect of the elastic modulus of a post on concentration, magnitude, and direction of dentinal stress was dependent on load direction. They showed that when highmodulus posts were modeled, horizontal loads caused more stress on the apical area of roots and such a load suggested a vertical root fracture.…”

Stress distribution on dentin-cement-post interface varying root canal and glass fiber post diameters. A three-dimensional finite element analysis based on micro-CT data

“…Tooth architecture is modified during endodontic treatment as a result of caries removal, access to the canal, and instrumentation in the root canal 17 . All these factors are associated with the higher internal stress induced in these teeth since this force is directly proportional to the fracture resistance and volume of the remaining dental structure 12 .…”