Besides having adequate dentinal moisture, agitation of the primers during application of two-step etch-and-rinse adhesives may be critical for optimal penetration into the demineralized collagen fibres. It also may aid the evaporation of residual water in the adhesive and hybrid layers, thus preventing nano leakage.
In a clinical trial comparing the performance of Prime & Bond NT using no rubbing action, slight rubbing action and vigorous rubbing action in the restoration of NCCLs, 92.5% of restorations in vigorous rubbing action group were found to retain after 24 months of clinical service. For the other two groups, the retention rates of the restoration were slightly lower, at 82.5%.