Effect of composite thickness over the fiber post on fracture resistance of endodontically treated teeth

Aim: This study aimed to assess the effect of composite thickness over the fiber post on fracture resistance of endodontically treated teeth. Methods: This in vitro, experimental study was performed on 50 sound human premolars, which were randomly divided into 5 groups (n=10). Teeth in Group 1 remained intact while other specimens underwent root canal treatment with a Mesio-occluso-distal (MOD) cavity preparation, restored with fiber posts with a distance of 1.5 mm to the occlusal surface in groups 2 and 4 and 0.5 mm in groups 3 and 5. 24 hours of incubation was applied for groups 1-3 and 1 year of incubation for groups 4 and 5. Thereafter fracture strength measured using a Universal Testing Machine at a crosshead speed of 1 mm/minute. Data were analyzed using Shapiro-Wilk, Two-Way ANOVA and Tukey HSD. Results: The results showed a significant difference in terms of fracture resistance (P 0.05). Also, Tukey HSD revealed no statistically significant differences between Group 1 and 4 at one year. However, Group 1 (1255.25±280.61N) exhibited significantly higher fracture resistance than that of Group 5 (855.72±300.20N) at one year (P=0.027). The difference between other groups was not significant at any time point (P>0.05). Conclusions: By covering the fiber post with 1.5 mm thickness of composite resin and cuspal reduction of 2 mm, the fracture resistance of endodontically treated teeth can be increased to the level of sound teeth.