Statement of problem: Endodontically treated teeth are known to have reduced structural strength. Glass fiber posts may influence fracture resistance and should be evaluated. Purpose: The purpose of this study was to evaluate the influence of glass fiber post length on the fracture resistance of endodontically treated teeth. Materials and methods: Forty intact human maxillary canines were selected and divided into four groups, the control group consisting of teeth restored with a custom gold cast post and core, with a length of two thirds of the root. Other groups received prefabricated glass fiber posts in different lengths: group I/III, removal of one third of the sealing material (5 mm); group I/II, removal of one half of the sealing material (7.5 mm); and group II/III, removal of two thirds of the sealing material (10 mm). All the posts were cemented with resin cement, and the specimens with glass fiber posts received a composite resin core. All the specimens were restored with a metal crown and submitted to a compressive load until failure occurred. The results were evaluated by one-way analysis of variance (ANOVA) and the all pairwise multiple comparison procedures (Tukey honestly significantly difference test; α = 0.05). Results: The ANOVA showed significant differences among the groups (p < 0.002). The Tukey test showed that the control group presented significantly higher resistance to static load than the other groups (control group, 634.94 N; group I/III, 200.01 N; group I/II, 212.17 N; and group II/III, 236.08 N). Although teeth restored with a cast post and core supported a higher compressive load, all of them fractured in a catastrophic manner. For teeth restored with glass fiber posts, the failure occurred at the junction between the composite resin core and the root. Conclusion: The length of glass fiber posts did not influence fracture load, but cast post and cores that extended two thirds of the root length had significantly greater fracture resistance than glass fiber posts.
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