Reinforcement effect of polyethylene fiber in endodonticaly treated teeth

Objective: The aim of this in vitro study was to evaluate reinforcement effect of polyethylene fiber use in endodontically treated molar teeth with MOD cavity. Methods: Sixty sound extracted human mandibular teeth were divided into 5 groups. Group 1 did not receive either cavity preparation or root canal treatment and served as positive control. Endodontic access and MOD cavities without proximal steps and flat floor were prepared in other groups. Following root canal treatment, Group 2 was kept unrestored and served as negative control. In Group 3 and 4, the teeth were restored with composite resin (CR) (AP-X, Kuraray, Japan) and dentin bonding system (DBS) (SE Bond, Kuraray, Japan). After finishing the restoration, in Group 4, a groove was prepared in buccolingual direction. A piece of polyethylene ribbon fiber (Ribbond, Seattle WA) was inserted inside the groove from buccal to lingual direction and the exposed fiber surface was covered with CR. In Group 5, polyethylene fiber was inserted into the cavities from buccal to lingual direction and the teeth were then restored with DBS and CR. After finishing and polishing, all specimens were stored in 100% humidity at 37oC for 1 day, compressive loading of the teeth were performed by a universal testing machine at a crosshead speed of 0.5 mm/min. Results: The mean load necessary to fracture the samples in each group were (in N): G1:1676.75±154.63a, G2:376.51±37.36b, G3:733.23±133.33c, G4:1231.48±134.03d G5: 943.63±121.15e. Data were submitted to ANOVA and Tukey Post-Hoc test that demonstrated differences among all groups showed above with different letters. Conclusions: (1) Unrestored teeth were significantly weaker than all the other groups. (2) Polyethylene fiber use before or after restoration significantly increased fracture strength. However inserting polyethylene fiber after restoration was much more effective than inserting the fiber under restoration.