What factor is essential for a successful fluoride varnish application?

The essential factor for a successful fluoride varnish application is the removal of biofilm before application. Biofilm, which consists of bacteria and other debris on the tooth surface, can prevent the fluoride from effectively penetrating the enamel to provide its protective benefits. By ensuring that the biofilm is removed, dental hygienists create a clean surface that allows for optimal fluoride absorption, maximizing its effectiveness in preventing caries and enhancing remineralization of teeth.

The other options may have relevance in a broader dental care context or could contribute to the overall procedure or patient education, but they are not as crucial as ensuring a clean surface prior to the fluoride application. For instance, applying fluoride varnish after a thorough cleaning or using a high concentration of fluoride may enhance outcomes, but without first eliminating biofilm, the application may not achieve its intended results. Additionally, while providing post-application care instructions is important for patient compliance and to ensure the treatment is effective over time, it does not directly influence the immediate success of the varnish application.