Influence of Cusp Reduction and Fiber Reinforcement on Cusp Deflection and Fracture Strength of Restored Endodontically Treated Molar Teeth

Abstract

Objective This study aimed to investigate the influence of various cusp reduction amounts, localization, and the use of coronal polyethylene fiber on cusp deflection in endodontically treated molar teeth. Material and methods The 120 intact molar teeth observed in the study were divided into 12 groups, and standard MOD cavities were prepared after the root canal treatment was completed. Groups 1 and 2 were determined as positive and negative control groups, respectively. Two cusp reductions were applied to Groups 3, 4, 5, and 6, and functional cusps reduction were applied to Groups 7, 8, 9, and 10. The cusp reductions were either 1.5 mm or 3 mm. After preparation, Groups 3, 5, 7, 9, and 11 were restored with Filtek One Bulk-Fill, while Groups 4, 6, 8, 10, and 12 were restored with Filtek One Bulk-Fill + Ribbond. As the teeth were restored, the amount of cusp deflection was measured with a twin channel deflection gauge device. The fracture strength of the teeth was measured using a universal test machine. The experimental results were statistically evaluated with two-way and one-way ANOVA tests. Results The reinforcement of the coronal structure with fiber reduced cusp deflection and increased fracture strength. The statistically significantly less cusp deflection was obtained in the groups with the same cavity design of having fiber placed than in the groups without fiber placed (p < 0.001). The statistically significantly lower fracture strength was obtained in Group 11 than all the reduced groups except Groups 5 and 7 (p < 0.05). The statistically lower fracture strength was obtained in Group 12, than in Group 4 (p < 0.05). Experimental groups with cusp reduction showed less cusp deflection (p < 0.001) and higher fracture strength (p < 0.05) than experimental groups without cusp reduction. Conclusions Fiber application and cusp reduction may have positive effects in terms of reducing cusp deflection and increasing fracture strength in direct restoration cases involving excessive substance loss in endodontically treated teeth. Clinical relevanceIncorporating cusp reduction and coronal fiber applications in treatment plans for endodontically treated teeth ensures that restorations are both functional and durable.