Fracture Resistance of Fiber-Reinforced vs. Conventional Resin Composite Restorations in Structurally Compromised Molars: An In Vitro Study.

Objective: The aim of this study was to evaluate reinforcing effect of different fiber-reinforced resin composites for restoring structurally compromised molars compared to conventional resin composite. Methods and Materials: Sixty healthy human third molars were randomly divided into six groups (n = 10). In G1 to G4, wide mesio-occluso-distal (MOD) cavities with an occlusal depth of 4 mm and proximal boxes with a width of 2/3 of buccolingual distance were prepared. In G5, after preparation of MOD cavities, 2 mm cusp reduction was made. The samples of G6 were remained intact (control). In G1 and G5, the conventional resin composite (G-ænial Posterior), and in G2, short fiber-reinforced resin composite (SFRC: EverX Posterior) were used. In G3 and G4, the Ribbond fibers were applied on base of cavity in buccolingual and cross-sectional direction, respectively, and followed by conventional resin composite restoration. After 24 h maintaining in distilled water at room temperature, fracture resistance of restored teeth was tested with a crosshead speed of 0.5 mm/s and fracture patterns were also evaluated by stereomicroscope (favorable: above cementoenamel junction (CEJ) and unfavorable: below CEJ). The data was analyzed using Shapiro-Wilk, one-way ANOVA, and post hoc Tukey's HSD tests. Results: The highest fracture strength was obtained in G2 (4051.4 ± 1293.9 N), which was significantly greater than G3 (2886.6 ± 720.4 N; p = 0.005) and G5 (2949.3 ± 307.5 N; p  = 0.010). No statistically significant difference was observed between other study groups. The greatest percentage of favorable fracture was recorded in G6 (70%) and G2 (60%). Conclusion: The reconstruction of severely weakened molar teeth with SFRC or incorporating of polyethylene fibers in cross-sectional direction on base of resin composite restoration improved fracture strength and favorably affected fracture modes in comparison to conventional posterior resin composite with or without cusp coverage.