Comparison of compression strength of direct composite endocrowns that reinforced with two different fibers in endodontic treatment premolars with exremely crown damage

Aim: The aim of this study is to compare the mechanical performance and fracture strength of direct composite endocrowns reinforced with two different fibers and prepared with two different cavity preparations in endodontically treated (ET) maxillary premolar teeth. Material and Method: Negatives of the teeth were obtained by pressing a soft essix plate before preparation on 90 healthy maxillary premolar teeth extracted for orthodontic and periodontal reasons. Endodontic treatment was applied to all teeth and the teeth were randomly divided into six groups (n=15). All teeth (90) were cut 3 mm above the enamel-cementum junction (CEJ) line. While the butt joint was prepared 3 mm above the 45 teeth CEJ line, ferrule was formed for 45 teeth with 2 mm axial extension and 1 mm chamfer step. While polyethylene fiber was applied to 30 teeth and glass fiber was applied to 30 teeth, no fiber was applied to 30 teeth. Group 1 (P1): Butt joint+ Polyethylene fiber, Group 2 (P2): Ferrule+ Polyethylene fiber, Group 3 (C1): Butt joint+ Glass fiber, Group 4 (C2): Ferrule + Glass fiber, Group 5 (K1) : Butt joint+ Fiberless, Group 6 (K2): Prepared as Ferrule+ Fiberless. All groups were placed on soft essix plates with the direct technique to apply bulk fill composite, and the original anatomical form of the crowns was obtained. Thermal aging was applied to the prepared groups at 25,000 cycles, between 5ºC-55ºC. The teeth were subjected to the vertical compression strength test at a crosshead speed of 1 mm/min. Data analysis and reliability assessment were performed using Two Way ANOVA (p< 0.05) and Bonferroni statistical analysis. Results: The mean compressive strength values between the groups were found to be P1: 497 N, P2: 442 N, C1: 522 N, C2: 579 N, K1: 402 N, K2: 429 N. The average polyethylene fiber group was 469 N, the average glass fiber group was 551 N, the average fiberless group was 415 N, and the overall average was 479 N. When the fracture strength was evaluated, the groups (polyethylene fiber, glass fiber, fiberless) were found to be statistically significant (p=0.005). The effect of cut configurations (butt joint, ferrule) on fracture strength values was not found statistically significant (p= 0.772). Groups and cut configuration were not statistically significant (p=0.361). Conclusion: Within the limits of this in vitro study; It was concluded that fiber reinforcement of endodontically treated maxillary premolar teeth restored with direct bulk fill composite resin endocrowns contributed to the fracture strength, and it was determined that the fractures that occurred were mostly repairable. Key Words: Polyethylene Fiber, Glass Fiber, Endocrown, Bulk Fill Composite Resin, Biomimetic Hydroxy Apatite (BHA)