Effect of Direct Composite and Indirect Ceramic Onlay Restorations on Fracture Resistance of Endodontically Treated Maxillary Premolars

Objectives: Fracture of endodontically treated restored teeth is a common concern. Premolars are subjected to high shear and tensile forces. This study aimed to assess the fracture resistance and fracture mode of endodontically treated premolars restored with direct and indirect onlay restorations. Materials and Methods: In this in-vitro experimental study, 45 human maxillary premolars were divided into three groups (n=15) of control (sound teeth), direct onlay, and indirect onlay. In groups 2 and 3, the teeth underwent endodontic treatment. Mesio-occluso-distal cavities were prepared and restored with direct composite (P60) and indirect IPS e.max ceramic onlays, respectively. The teeth were subjected to vertical forces after cyclic loading. The maximum load causing fracture was recorded in Newtons. Data were analyzed using analysis of variance, chi-square test, and Tukey’s test. Results: The highest and the lowest fracture resistances were noted in sound teeth and direct onlay restorations, respectively. The difference in fracture resistance was significant among the three groups (P<0.001). Pairwise comparisons revealed a significant difference in the fracture resistance of sound teeth and the two restoration groups (P<0.001). However, the difference in the fracture resistance of direct and indirect onlay restorations was not significant (P=0.6). Chi-square test showed a significantly higher frequency of irreparable fractures in the indirect onlay group (P=0.005). Conclusion: Direct and indirect onlay restorations were not significantly different in terms of the fracture resistance but the frequency of irreparable fractures was higher in indirect restorations.