Fracture Resistance of Teeth Restored With Different Fiber-Reinforced Composites: A Comparative In Vitro Study

Restoration of extensively damaged posterior teeth poses a clinical challenge because of the high risk of fractures associated with wide mesio-occluso-distal (MOD) cavities. Conventional nanohybrid composites, although esthetically satisfactory, often fail to reinforce weakened cusps under occlusal stress. Fiber-reinforced composites (FRCs) have emerged as promising alternatives for enhancing flexural strength, fracture toughness, and stress distribution across the restoration-tooth interface. The present in vitro study aimed to compare the fracture resistance of mandibular molars with standardized MOD cavities restored using different FRC systems and conventional composite resins.

Forty freshly extracted human mandibular molars of similar size and morphology were selected, and standardized MOD cavities were prepared using a high-speed handpiece under water cooling. The samples were randomly divided into four groups (n=10 each). Group 1 (control) was treated with a nanohybrid composite resin (NeoSpectra ST; Charlotte, NC: Dentsply Sirona). Group 2 was restored with FibraFill Dentin (Jičín, Czech Republic: Dentapreg) combined with NeoSpectra ST. Group 3 incorporated Ribbond polyethylene fiber (Seattle, WA: Ribbond Inc.) at the cavity base, whereas Group 4 used EverStick C&B (Tokyo, Japan: GC Corporation) glass fiber beneath the composite restoration. All restorations were performed using standardized etching, bonding, and incremental curing techniques. The specimens were stored in distilled water at 37°C for 24 h before testing. The fracture resistance was evaluated using a Universal Testing Machine (Norwood, MA: Instron) with a crosshead speed of 2 mm/min until fracture occurred. Data were statistically analyzed using one-way analysis of variance (ANOVA) followed by post-hoc Tukey's test, with the significance level set at p<0.05.

The mean fracture resistance values were highest for EverStick (2759.5±1163.33 N), followed by FibraFill Dentin (2371.1±586.36 N), Ribbond (2057±321.93 N), and the lowest for the control group, NeoSpectra ST (1655.3±345.2 N). The differences between the groups were statistically significant (p=0.008). Pairwise comparisons using the post-hoc Tukey's test revealed that EverStick showed significantly greater reinforcement than NeoSpectra ST (p=0.006). Other comparisons, including NeoSpectra ST versus FibraFill Dentin, NeoSpectra ST versus Ribbond, FibraFill Dentin versus Ribbond, FibraFill Dentin versus EverStick, and Ribbond versus EverStick, did not show statistically significant differences (p>0.05).

Within the limitations of this in vitro study, it can be concluded that the incorporation of FRCs considerably improves the fracture resistance of teeth with large MOD cavities compared with conventional composites. Among the tested materials, EverStick glass fiber exhibited the best performance, followed by FibraFill Dentin and Ribbond.