Aims: This study assessed the effect of preheating nano-hybrid and bulk-fill composites with warm airstream on their microtensile bond strength (MTBS) to dentin.
Materials and Methods: In this in vitro study, dentin was exposed in 42 extracted premolars that were assigned to two groups ( = 21) for bonding to EverX Posterior bulk-fill and Grandio nano-hybrid posterior composite. Each group was subdivided into three subgroups for preheating of composite to 50��C by a commercial composite warmer (Subgroup 1), a warm airstream by a hair dryer for 10 s (Subgroup 2), and no heating (room temperature; Subgroup 3). Composite cylinders with a 4-mm height were bonded to the tooth surface with a 5-generation bonding agent using the incremental technique and cured (each increment for 30 s). The MTBS to dentin was measured, and the bonding interface was evaluated under a stereomicroscope and a scanning electron microscope (SEM). Data were analyzed using one-way and two-way ANOVA, Tukey's test, and independent t-test (�� =0.05).
Results: In both composite groups, the mean MTBS of the warm airstream subgroup was significantly higher than that of warmer ( < 0.001) and control ( < 0.001) subgroups. The mean MTBS of the warmer subgroup was significantly lower than that of control subgroup ( = 0.01). The MTBS of the EverX composite was significantly higher than that of the Grandio composite only in the warmer group ( < 0.05). Adhesive failure occurred more frequently in all groups with the highest frequency in airstream subgroup of both composite types.
Conclusion: Preheating with a warm airstream significantly increased the MTBS of both composite types to dentin.
