Fracture Resistance of Maxillary Premolar Teeth Restored with Bulk Fill Resin Composite: In-vitro Study

Aim of the study: To evaluate the fracture resistance of maxillary premolar teeth with MOD cavities restored with different bulk fill resin composite systems In-vitro.
Materials and methods: Seventy maxillary premolars were selected and divided into seven groups n=10. The first group was left intact and considered as positive control group (In). Class II MOD cavities were prepared in the remaining groups. The second group was left prepared unrestored and considered as negative control group (Un). Five different resin composite systems were to restore the cavities. The first one was incremental fill resin composite Z350 XT (ZX) and the third group was considered as control group. The remaining resin composite systems were of bulk fill type and were as follow: Tetric^® N Ceram Bulk-Fill (TB), Filtek Bulk Fill (FB), SonicFill2^™ (SF) and Reveal^® HD Bulk (RV). All the groups were thermocycled (Robota, Egypt) for 5000 cycles. Fracture resistance test was performed immediately after thermal aging process by (Instron 3345, Canton, MA, USA). Fracture patterns were examined under stereomicroscope and recorded. Samples for each fracture pattern were examined under SEM. Data was tabulated then analyzed using One-way analysis of variance (ANOVA) followed by t-test in order to determine significant differences among groups (P= 0.05).
Results: There was no statistical significant difference (P≤ 0.05) between FB, SF groups. On the other hand, there was a significant difference between In, Un, ZX, TB, RV groups (p= 0.0001). Additionally, there was a significant difference between (FB, SF) groups and the remaining groups (p= 0.0001).
Conclusion: Based on the current study, both incremental-fill and bulk-fill resin composite systems did not restore the fracture resistance of the sound teeth.  However, the use of bulk fill resin composite (Tetric N Ceram) has a positive effect on the fracture resistance of the maxillary premolar. On the other hand, the other bulk fill resin composites showed comparable fracture resistance values with incremental-fill resin composite systems.