Effect of fiber post materials and timing of coronal preparation on sealing ability of post-core systems: A factorial design study.

PURPOSE: To examine the effects of fiber post material and coronal preparation timing on the sealing ability of post-core systems and to determine whether these factors interact under thermal and mechanical aging conditions. METHODS: A 2×2 factorial design was used. 60 freshly extracted single-rooted premolars meeting predefined inclusion and exclusion criteria were randomly assigned to four groups (n= 15): fiber-reinforced composite (FRC) post with immediate preparation, FRC with delayed preparation, prefabricated quartz fiber (PQF) post with immediate preparation, and PQF with delayed preparation. Post space length was standardized to 10 mm while maintaining a 4 mm apical seal, in accordance with the recommendation that post length should approximate two-thirds of root length and at least equal the clinical crown height. All procedures were completed by a single prosthodontist. Specimens underwent 5,000 thermal cycles followed by 240,000 cyclic loading cycles. Interfacial microgap width was serially evaluated by SEM at two time points, namely after thermocycling and after cyclic loading, and the data were analyzed with a linear mixed-effects model. RESULTS: Post material type (F= 45.32, P< 0.001, η²p= 0.43) and time point (F= 312.56, P< 0.001, η²P= 0.84) showed significant effects, as did the material x time interaction (F= 8.73, P=0.004, η²P= 0.13). Preparation timing was not significant (F= 2.15, P= 0.148). After thermocycling, group B showed smaller microgap width than group D (3.91± 0.87 vs. 5.62± 1.77 µm; mean difference, -1.71 µm; 95%CI: -2.76 to -0.66; P=0.003). After cyclic loading, Group A was smaller than Group C (13.97± 1.89 vs. 17.85± 2.83 µm; mean difference, -3.88 µm; 95%CI: -5.62 to -2.14; P< 0.001), and Group B was smaller than group D (8.84± 1.98 vs. 13.29± 2.85 µm; mean difference, -4.45 µm; 95%CI: -6.22 to -2.68; P< 0.001). No root fractures were detected during specimen preparation, thermocycling, or cyclic loading. CLINICAL SIGNIFICANCE: For a given fiber post material, immediate and delayed coronal preparation produced comparable marginal sealing. Compared with prefabricated quartz fiber posts, fiber-reinforced composite post-core systems provided superior interfacial stability after aging and may be preferable in roots with irregular or flattened canal morphology.