Effect of application delays on the dentin bond strength and interfacial morphology of different adhesive systems: an SEM analysis

This study evaluated the effect of application delays on the dentin bond strength of different adhesive systems used in composite restorations. Forty-five extracted human molars were randomly assigned to Clearfil SE Bond, G-Premio Bond, and Single Bond Universal ( n = 15). Each adhesive was subdivided according to application time: immediate use, 3-minute delay, and 5-minute delay ( n = 5). Adhesives were applied to occlusal dentin surfaces according to manufacturers’ instructions, followed by composite build-up procedures. Microtensile bond strength (µTBS) was evaluated using a universal testing machine, and failure modes were examined microscopically. Selected specimens were analyzed using scanning electron microscopy (SEM). Adhesive system (F = 48.32, p < 0.001) and application time (F = 22.72, p < 0.001) significantly influenced µTBS. The highest bond strength was observed in the immediate Clearfil SE Bond group (34.5 ± 4.8 MPa), whereas the lowest value was recorded in the 5-minute delayed G-Premio Bond group (13.4 ± 2.8 MPa). A 5-minute delay significantly reduced bond strength in all adhesive systems, whereas a 3-minute delay generally did not affect bonding performance. More than 85% adhesive failures were observed in the 5-minute delay groups. SEM analysis revealed porosity and crater-like surface defects in delayed universal adhesive groups. A 5-minute application delay significantly compromised dentin bond strength and increased adhesive failures. Immediate adhesive application is recommended to preserve bonding effectiveness and optimize restoration longevity.