Fracture resistance, 3-dimensional finite element analysis, and safety factors for five post-and-core restorations with crowns placed in the noncircular-shaped canals of premolars.

Abstract

Statement of problem: Restoring endodontically treated premolars with noncircular canals presents a significant challenge.

Purpose: The purpose of this study was to compare the in vitro fracture resistance and the finite element computational calculation-based stress and safety factor of noncircular-shaped, endodontically treated premolars restored with 5 different prefabricated and custom computer-aided design and computer-aided manufactured post-and-core systems.

Material and methods: Fifty single-rooted oval-shaped canal maxillary premolars were endodontically treated and post spaces were prepared. The specimens were divided into 5 categories on the basis of the post-and-core system used: Group CN composite resin core without a post, Group CF prefabricated fiber-reinforced composite resin post and composite resin core, Group IC interpenetrating phase composite post-and-core, Group LS lithium disilicate post-and-core, and Group ZR zirconia post-and-core. Lithium disilicate crowns were fabricated and cemented on the 5 different post-and-core systems and subjected to a fracture resistance test using a spherical indenter with static loading. Differences in fracture resistance were evaluated using a 1-way analysis of variance (ANOVA) (α=.05). The 3-dimensional finite element method was used to determine the von Mises stress and safety factors, defined as the ratio of the material's strength to the von Mises stress experienced, within different compartments of the restored tooth model.

Results: In the in vitro fracture resistance test, the mean ±standard deviation fracture loads of the 5 groups were 2144 ±515 N, 1801 ±600 N, 1690 ±312 N, 1612 ±545 N, and 1487 ±600 N, respectively and were statistically similar (P=.078). All specimens within the ZR group exhibited restorable fractures. In contrast, only 30% of the CN group specimens showed restorable fractures. The incidence of restorable fractures in the CF, IC, and LS groups was 70%, 80%, and 70%, respectively. Although all groups showed similar maximum von Mises stress and stress distribution, safety factors in the models varied significantly. The ceramic crown was the weakest component in the LS and ZR groups, with much lower safety factors than dentin and post-and-core regions. Additionally, the CN group's wider dentin area had a demonstrably lower safety factor.

Conclusions: Endodontically treated noncircular-shaped canal premolars showed minimal effect on fracture resistance regardless of post type. However, for teeth with sufficient ferrule, using any post-and-core system significantly reduced the incidence of nonrestorable fractures compared with just a coronal foundation restoration, with custom zirconia offering the potential of achieving a restorable outcome after fracture.