Evaluation of Cuspal Deflection and Fracture Strength of Endodontically Treated Teeth Restored with Different Restorative Material Combinations

Objective: This study evaluated the effects of restorations using varied materials and their combinations on cuspal deflection and fracture resistance of endodontically treated MOD cavitated maxillary premolars. Materials and methods: 168 premolar teeth were used in the study. MOD cavities were prepared, and endodontic treatments were performed. Subsequently, the teeth were divided into 14 groups. Group 1 was the positive control (healthy teeth), and Group 2 was the negative control (MOD cavity only). In Groups 3-7 and Groups 9-13, EverX Posterior, SDR Plus Bulk Fill Flowable, G-aenial Universal Injectable, Biodentine, and Fuji II LC were used as the base layer, respectively. In Groups 3-7, Filtek One Bulk-Fill Restorative was used as the top layer, while in Groups 9-13, Tetric N-Ceram was used. Group 8 was entirely restored with Filtek One Bulk-Fill Restorative and Group 14 with Tetric N-Ceram. Cusp deflection was measured. Fracture resistance testing was performed. Results: Within each group, there was a statistically significant decrease in cusp deflection change values at all measured time points (p <0.05). In intergroup comparisons, significant differences were found in cusp deflection change values at all times only in groups where EverX Posterior was applied as the base layer (p <0.05). In the groups where Filtek One was used, differences were seen between the groups at all times (p<0.05).Groups 4 and 5 exhibited fracture resistance similar to the positive control group (p>0.05). In the comparison between groups, a significant difference was seen in terms of fracture strength only in the groups where EverX Posterior and SDR Plus Bulk Fill Flowable were used as the substrate (p <0.05). Conclusions: Different materials and combinations of these materials produced different fascial deflection and fracture strength endodontically treated teeth. Clinical Relevance: When performing coronal restoration of an endodontically treated tooth, it is recommended to select and use the appropriate restorative material, taking into account the position of the tooth in the mouth and the amount of material loss.