The effect of fiber insertion on fracture strength and fracture modes in endocrown and overlay restorations

Aim of this study was to determine the fracture strength and modes of endocrown and overlay restorations with/without fiber reinforcement on endodontically treated teeth. Sixty-five molar teeth were used: Group IN (intact teeth), Group E (endocrown), Group ER (endocrown + ribbond), Group O (overlay), Group OR (overlay + ribbond; n = 13). Ribbond (Seattle, WA) was inserted at the base of pulp chamber in Group ER and OR. All restorations were designed and produced by using computer-aided design and computer-aided manufacturing (Sirona Dental Systems, Bensheim, Germany) and Cerasmart (GC Corp. Kasugai, Aichi, Japan). All teeth were subjected to thermomechanical aging and fractured in a universal test device. Fractured surfaces were analyzed with a stereomicroscope (SMZ1000, Nikon, Japan). Data were analyzed with Welch's analysis of variance and Games–Howell test (p <.001). Group E showed significantly lower fracture strength values than other groups(p <.05). No statistically significant differences were found among the other groups(p >.05). Most of the unfavorable fractures were seen in Groups E and O. Overlay restorations showed higher fracture strength values than endocrown restorations. Although fiber insertion did not improve the fracture strength of the indirect restorations, it reduced the frequency of irreparable fracture mode. Overlay restorations and fiber application are more advantageous in preserving the durability of the endodontically treated teeth.