Fracture Resistance of Endodontically Treated Teeth Restored with Preheated Short Fiber-Reinforced Composite and Preheated Composite Resin

This study aimed to assess the fracture resistance and fracture patterns of endodontically treated permanent mandibular molars restored with either preheated or nonpreheated conventional composite resin or short fiber-reinforced composite resin (SFRC). One hundred and twenty mandibular molars with prepared mesio-occluso-distal (MOD) cavities were allocated to six groups: positive control (intact teeth, no restoration, <i>n</i> = 20), negative control (endodontically treated but unrestored, <i>n</i> = 20), and four experimental groups restored with conventional composite, preheated composite, SFRC, or preheated SFRC (<i>n</i> = 20 each). After thermocycling, fracture resistance was tested using a universal testing machine at 0.5 mm/min. Data were analyzed using Jamovi software (Version 2.4.8; The Jamovi Project, Sydney, Australia). Normality was assessed with the Kolmogorov-Smirnov test. Group differences were evaluated using the Kruskal-Wallis test followed by the Dwass-Steel-Critchlow-Fligner post hoc test. The association between fracture modes and fracture strength categories was examined using the chi-square test of independence. A <i>p</i>-value < 0.05 was considered statistically significant. The positive control showed significantly greater fracture strength than all restored groups (<i>p</i> < 0.05). All restored groups had significantly higher fracture resistance than the negative control (<i>p</i> < 0.05), with no significant differences among the restored groups (<i>p</i> > 0.05). A significant association was found between fracture mode and fracture strength (χ²(1) = 6.97, <i>p</i> = 0.008). The preheated SFRC group showed a higher rate of restorable fractures compared to others, suggesting improved clinical reparability with preheating.