Fracture Resistance of Different Fibre-reinforced Composite Restorations in Cervical Lesiondirected Access Cavities of Mandibular Premolars: An In-vitro Analysis

Introduction: Endodontically Treated Teeth (ETT), especially mandibular premolars, are prone to fracture due to structural weakening and cervical lesions. Conventional straight-line access often results in excessive coronal dentin removal, further compromising strength. This study investigates a novel cervical lesion-directed access approach and evaluates the effect of Polyethylene Fibres (PF), Glass Fibres (GF) and their combination on fracture resistance. Aim: To compare the fracture resistances of different fibrereinforced combinations as access cavity restorative materials in cervical access cavities. Materials and Methods: The current in-vitro study was conducted at the Department of Conservative Dentistry and Endodontics, Sibar Institute of Dental Sciences, Guntur, Andhra Pradesh, India from October to December 2025. Sixty extracted human mandibular premolars with single canals and intact crowns were selected from the 18-40 years age group, irrespective of gender distribution. Cervical lesion was mimicked by preparing uniform wedge-shape cavities in Cemento-Enamel-Junction (CEJ) of buccal surfaces of all teeth, followed by Cervical Lesion-Directed Access Cavity (CLDAC) preparation and root canal preparation with ProTaper Gold rotary files up to F3. Canals were obturated and samples were randomly allocated into six groups (G1-G6, n=10 per group): G1 (control group)- intact teeth, G2- ETT without restoration, G3- ETT restored with nanohybrid composite, G4- ETT restored with composite and PF, G5- ETT restored with composite and GF, and G6- ETT restored with composite and combined PF and GF. Specimens mounted in acrylic resin did undergo fracture resistance testing in a Universal Testing Machine (UTM). Statistical analysis was performed using One-way Analysis of Variance (ANOVA) and Tukey’s post-hoc test (p≤0.05). Results: The highest fracture resistance was observed in intact teeth (994.00 N), followed by GF-reinforced composite (846.00 N), combined fibre reinforcement (793.00 N), PF reinforcement (746.00 N), and composite alone (594.00 N). The lowest values were recorded in unrestored teeth (280.00 N). All intergroup differences were statistically significant (p<0.001). Conclusion: GF reinforcement showed the highest strengthening effect. Using fibres in combination produced a synergistic benefit, while PF offered moderate improvement compared to composite alone. Overall, GF-reinforced composite appears to be the most effective restorative option for CLDAC.