Fluoride Varnish

Fluoride varnish is a highly concentrated form of fluoride that is applied on to tooth surfaces with a brush.  It is 5% sodium fluoride except Enamel Pro Varnish which is formulated to deliver ACP (Amorphous Calcium Phosphate).  Varnish is packaged in pre-measured uni-dosage form.  Some varnish contain saccharin or aspartame for artificial sweetness but there are other products sweetened with neutral sugar like xylitol, which has shown to reduce dental caries.  Gluten free varnish is also available for patients with gluten sensitivity. 

Prevention of root caries: a literature review of primary and secondary preventive agents. Special Care in Dentistry. 2013
This study reviewed and summarized the effectiveness of root caries preventive agents: fluoride, chlorhexidine, xylitol, amorphous calcium phosphate (ACP), sealants, saliva stimulators, or silver diamine fluoride.  38% silver diamine fluoride was the best choice in preventing dental caries, however, silver diamine fluoride has not been approved by the FDA for clinical use in the United States.  The next best choice to prevent root caries was application of a 22,500ppm(5%) Sodium Fluoride Varnish every 3 months.