Comparative finite element analyses of stress exerted on the dentin by intraradicular posts

The amount of residual dentin thickness and tooth position in the dental arch is crucial to determine whether an intraradicular post should be used. This study aimed to compare stress distribution on the root dentin of an endodontically treated tooth rehabilitated with CAD/CAM milled glass fiber posts (MP), cast metal posts (CMP), or prefabricated posts (PP) with or without ferrule support, using the finite element method.

A human upper central incisor was selected, scanned, and treated endodontically. The canal was then prepared for post-placement and scanned again for the fabrication of digital posts. The geometries of MP and CMP were based on the measurements made by digital scanning of the root canal. In contrast, the geometry of PP was determined by technical drawings provided by the manufacturer, taking into account the post-space preparation and the cement. Six digital models were established: MP1 with ferrule support, MP2 without ferrule support; CMP1 with ferrule support, CMP2 without ferrule support; PP1 with ferrule support, and PP2 without ferrule support. The simulation was performed using the finite element method.

Oblique forces were identified as more relevant to the metallic element compared to vertical forces. The presence of a ferrule was considered a protective factor for the remaining tooth structure. When the ferrule was absent, stresses were more evenly distributed in MP compared to CMP and PP. Posts with a higher modulus of elasticity were associated with higher and unequal stresses in the root dentin, which could predispose the tooth to fractures.

As for the restoration set as a whole, it can be concluded that stress distribution on the root dentin was more evenly distributed on the milled post than on the other posts when a ferrule was absent, and the oblique forces were more detrimental to the tooth structure than vertical forces and that ferrule support was a protective factor for the remaining tooth structure.

The results of the study provide valuable information on how different types of intraradicular posts and the presence of a ferrule affect the stress distribution in dentin. In the absence of a ferrule, milled and customized computer-aided design/computer-aided manufacturing (CAD/CAM) glass fiber posts can exhibit better fracture resistance and adhesion strength than prefabricated fiberglass posts and metal posts.