Cuspal Deflection and Fracture Resistance of Maxillary Premolars with Complex Class II and Restored with Contemporary Bulk-Fill Resin Composite

Objective: This study aimed to evaluate cuspal deflection (CD) and fracture resistance (FR) of maxillary premolars with Mesio-occluso-distal (MOD) cavities and restored with conventional and bulk-fill resin composites. Materials and Methods: One conventional (Filtek Z350XT) and two recent bulk-fill (Aura, and Reveal HD) resin composites were used. A total number of 120 maxillary premolars were used in this study. For CD test, 45 maxillary premolars prepared with standardized MOD cavity preparations and were divided into three groups (n=15). The different three resin composites (RCs) were used to restore the three groups. The CD values were measured using a digital micrometer five minutes after restoration completion. For FR test, 75 maxillary premolars were divided into five groups (n=15), positive control group (intact unprepared), and four groups received MOD cavities, negative control (prepared unrestored), and three groups restored as in CD test. A universal testing machine (Instron) was used to measure FR in Newton (N), and mode of failure was assessed. Results: The mean CD was significantly different in the three groups (p≤0.001). The highest deflection was noted in Filtek Z350XT (12.73±2.52 μm), the lowest was noted in Aura BF (5.60±0.74 μm). Highest FR was noted in the positive control group (1502±183.85 N) with significant difference with other groups (p≤0.001), followed by Aura BF (964.3±183.8 N) and Filtek Z350 XT (927.62±177.1 N) with no significant difference (p=0.501). The lowest FR value within the restored groups was noted in Reveal HD BF (787.9±98.2 N), and the negative control group revealed the lowest FR value in all tested groups (353.9±40.51 N). There was no significant difference between the materials regarding the failure mode. Conclusion: Bulk-Fill resin composites had less significant CD. However, fracture resistance values were material dependent.