Effect of preheating nano-hybrid and bulk-fill composites with warm airstream on their microtensile bond strength to dentin.

Abstract

This study assessed the effect of preheating nano-hybrid and bulk-fill composites with warm airstream on their microtensile bond strength (MTBS) to dentin. In this in vitro study, dentin was exposed in 42 extracted premolars that were assigned to two groups (n = 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 5th-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 (α =0.05). In both composite groups, the mean MTBS of the warm airstream subgroup was significantly higher than that of warmer (P < 0.001) and control (P < 0.001) subgroups. The mean MTBS of the warmer subgroup was significantly lower than that of control subgroup (P = 0.01). The MTBS of the EverX composite was significantly higher than that of the Grandio composite only in the warmer group (P < 0.05). Adhesive failure occurred more frequently in all groups with the highest frequency in airstream subgroup of both composite types. Preheating with a warm airstream significantly increased the MTBS of both composite types to dentin.