Fracture resistance of direct composite and composite onlay on endo-treated upper premolar with MOD cavity

Endodontically-treated teeth are weaker than vital teeth due to extensive missing sound tooth structure and the endodontic treatment. The restoration choice for an endodontic treatment tooth (ETT) determines the ETT’s survival. This study aims to investigate the fracture resistance and mode of direct composite restoration and direct composite onlay with cuspal coverage on endodontically-treated upper premolars with mesio-occluso-distal (MOD) cavity. Twenty sound upper premolars were collected from local dental clinics, mounted in cold-cure acrylic and stored in normal saline. Teeth were subjected to root canal treatment (RCT), followed by MOD cavity preparation. The teeth were randomly and equally divided into two groups (Groups A and B). Group A (n = 10) were restored with direct composite restoration, whereas Group B (n = 10) were prepared occlusally and restored with direct composite onlay restoration. All teeth were subjected to a compressive axial load test using a universal testing machine (Instron 3369, United State) with a metal ball sized 4 mm at 1mm/min of crosshead speed until a fracture occurred. The fracture mode was analysed under a stereomicroscope with 0.68 magnifications. A statistical analysis of fracture resistance and fracture mode was performed using a paired T-test. The mean fracture resistance value was 431.37 N for group A and 1158.34 N for group B, with a statistically significant difference (p< 0.05) between these two groups. Endodontically-treated upper premolar with MOD cavities restored with direct composite onlay restoration exhibited higher fracture resistance than direct composite restoration. In addition, the mode of fractures was not affected by the types of restoration.