Effect of simulated root canal morphology and post space depth on fracture performance of glass fiber-reinforced post-core buildups

Abstract

Objectives: This in vitro study evaluated the effect of simulated root canal morphology, post space depth (PSD), and type of glass fiber-reinforced composite (GFRC) on the fracture strength and failure mode of post-core buildups. Materials and methods: A total of 168 3D-printed maxillary premolar root models were allocated into 24 groups (n = 7) based on simulated canal morphology (single-circle, oval, double-circle), PSD (4 mm, 6 mm), and GFRC type (everStick, everX-flow, everX-posterior), with Itena post as the control. A standardized adhesive protocol was used, followed by GFRC application and dual-cure core buildup. Fracture strength was tested under a 45° compressive load. Failure modes were categorized as favorable (type I, II, III) or unfavorable (type IV). Data were analyzed using ANOVA with Tukey’s post hoc test, independent t-tests, and chi-square tests (α = 0.05). Results: GFRC type significantly affected fracture strength (p < 0.001), whereas neither simulated canal morphology nor PSD showed a significant effect. At 4 mm PSD, everX-flow exhibited significantly lower fracture strength than Itena and everStick posts in single-circle and oval canal models (p < 0.05). At 6 mm PSD, everX-flow recorded the lowest fracture strength in single-circle canal models (p < 0.05). Failure mode was significantly influenced by PSD (p = 0.01) and GFRC type (p < 0.001). A 6 mm PSD was associated with a higher percentage of each favorable failure type compared to 4 mm PSD. EverStick and Itena posts showed the highest percentage of favorable failures. Conclusions: The intra-canal reinforcing material is the primary determinant of the fracture performance of post-core buildups. The mechanical reinforcement materials of everStick and everX-posterior posts but not everX-flow are comparable to that of Itena post. Clinical relevance: Everstick and everX-posterior can replace Itena posts as safe reinforcing materials in single-canaled premolars.