Effect of Reduced Universal Adhesive Application Time on Enamel Bond Fatigue and Surface Morphology

Objective: The purpose of this study was to evaluate the effect of reduced application times of universal adhesives on enamel bond fatigue and surface morphology of the treated enamel with constant force atomic force microscopy (AFM). Methods: Four universal adhesives-Adhese Universal (AU), Clearfil Universal Bond Quick (CU), G-Premio Bond (GP), and Scotchbond Universal Adhesive (SU)-were evaluated in a laboratory for their ability to adhesively bond resin composite to enamel. Shear bond strengths were initially determined using 15 specimens per test group for each adhesive. Shear fatigue strengths were then determined using 20 specimens per test group for each the adhesives. The fatigue specimens were loaded using a sine wave at a frequency of 20 Hz for 50,000 cycles or until failure occurred. AFM observations, surface Ra roughness measurements, and geometric surface area evaluations of enamel surface treated with the adhesive agents were also conducted. Results: A strong relationship was found between the initial shear bond strength and shear fatigue strength for enamel surface Ra roughness but not for geometric surface area. The initial shear bond strength and shear fatigue strength of CU and GP were not influenced by different application times, unlike those of AU and SU. While the surface area of enamel treated with the adhesive agents was not significantly influenced by different application times and type of adhesive, surface Ra roughness of the enamel in the AU and SU groups significantly increased with increasing application time, unlike CU and GP. Conclusions: The results of this study suggest that universal adhesives, used with reduced application times, have adequate Ra surface roughness to provide sufficient resistance to enamel bond fatigue at application times from <1 second to 20 seconds, while the geometric surface area of adhesive-treated enamel did not show any significant changes at these different application times.