Finite element analysis of strength and adhesion of cast posts compared to glass fiber-reinforced composite resin posts in anterior teeth

Statement of problem: Previous studies on the strength of teeth restored with posts have not resolved the controversy as to which post systems provide the greatest strength and longevity.

Purpose: The purpose of this study was to compare the strength of teeth restored using cast posts with those restored using glass fiber-reinforced composite resin posts and to evaluate the bond strength of the posts to dentin.

Material and methods: The investigation was conducted by using finite element analysis, combined with the application of contact elements. Three-dimensional (3-D) models of the maxillary central incisors were generated: IT, an intact tooth; CC, a tooth with a ceramic crown; FP, a tooth restored with an FRC (glass fiber-reinforced composite resin) post; CPAu, a tooth restored with a gold alloy cast post; and CPNi, a tooth restored with an NiCr (nickel chromium alloy) cast post. Each model was subjected to vertical and oblique loads with a force of 100 N. To evaluate the strength of the restored tooth, ceramics, and composite resin, the modified von Mises failure criterion was used, the Tsai-Wu criterion for FRC, and the von Mises criterion for gold and NiCr alloy. The equivalent stresses found in the tested models were compared with the tensile strength of the respective materials. Contact stresses in the luting cement-dentin interface were calculated.

Results: The maximum mvM (modified von Mises failure criterion) stresses in the dentin of the teeth restored with FRC posts were reduced by 21%, and in those restored with cast NiCr posts, stresses were reduced by 25% when compared to the stresses in the intact tooth. The equivalent stresses in metal posts were several times higher than in FRC posts, but did not exceed the tensile strength of the materials. The highest mvM stress in the luting resin cement around the FRC post was 55% higher than in the luting resin cement around the metal post, under an oblique load. In the ceramic crown, which covered the composite resin post and core, the highest mvM stress was 30.7 MPa, whereas with the metal post and core, it was 23 MPa.

Conclusions: Cast metal posts resulted in lower stresses in the dentin of the restored teeth than did FRC posts. Irrespective of the material, the equivalent stresses in the posts did not exceed their tensile strength. Lower stresses were present in the luting cement and the cement-dentin interface around cast posts than around FRC posts. In the ceramic crown supported by a metal post and core, the stresses were lower than those observed in the crown supported by a composite resin core foundation.