Comparative Evaluation of Microshear Bond Strength and Microgap Formation of a New Self-Cure Bulk-Fill and a Light-Cure Composite Resin in Bonding to Dentin.

Aim: This study aimed to compare the microshear bond strength (μSBS) and microgap formation of STELA self-cure composite and a light-cure composite when bonded to dentin. Material and Methods: A total of 45 bovine teeth were divided into three groups: (1) STELA composite with STELA primer (SS), (2) STELA composite with Clearfil SE Bond (S6), and (3) Luna light-cure composite with Clearfil SE Bond (L6). Each sample was bonded to dentin, subjected to artificial aging, and tested for μSBS using a universal testing machine with the wire loop technique. Failures were categorized as adhesive, cohesive, or mixed. Microgap formation at the dentin-composite interface was evaluated under a scanning electron microscope (SEM) at 1000× magnification. The average and maximum gap values were recorded. Data analysis was conducted using SPSS version 16, with statistical significance set at 0.05. Results: The L6 group exhibited significantly higher mean μSBS compared to both the S6 and SS groups (p < 0.001). Additionally, the SS group showed significantly higher bond strength than the S6 group (p=0.002). Adhesive failures were the most common in all groups, with cohesive failures in the composite being more frequent in the L6 group. However, the distribution of failure types did not differ significantly among groups (p=0.385). Microgaps in the L6 and SS groups were limited and comparable, although slightly higher in the SS group. The S6 group exhibited the largest maximum and mean microgaps, with gaps often extending across the entire interface. Conclusion: This study showed the highest bond strength in the light-cure composite, followed by STELA with its primer and then with Clearfil SE Bond. The largest microgap occurred in self-cure STELA with Clearfil SE Bond. STELA should be used with its specific primer, as Clearfil SE Bond is not a suitable substitute.