This study aimed to investigate the effects of different fiber implantation techniques on the microleakage of MOD cavities and fracture resistance in molar teeth. The study was conducted in two phases: the microleakage test group (T2) and the fracture resistance test group (T1). There was a randomization of 110 third molars (T1:n1/4 = 80, T2:n1/3 = 30). Group K was the composite restoration (Gaenial Posterior, GC); group KFT was the cavity lined with polyethylene fiber (Ribbond, Ribbond Inc., Seattle, WA, USA) + composite restoration; group KFH was the polyethylene fiber placed circumferentially on the cavity's inner walls + composite restoration; and group KFT was the MOD cavities restored following standard preparation. Teeth in the T1 control group were not damaged. Types of fracture, fracture strengths, and microleakage values were evaluated. The Kruskal Wallis H and Mann-Witney U tests were used for statistical analysis. It was found that there was no significant difference in fracture strength between the groups (P > 0.05). Compared with the K group, there were more restorable fracture types in the KFT and KFH groups. The microleakage values in the KFT and KFH groups were significantly lower than those in the K group (P < 0.05), but they were not different from each other (P > 0.05). These results indicate that the use of polyethylene fibers in MOD cavity restoration offers an advantage for composite restorations.
