Fluoride varnish is sodium fluoride.  Advantage Arrest is free, ionic fluoride.  Once you factor out the weight of the sodium in fluoride varnish, the 5% works out to 22,600 ppm F rather than 50,000 ppm F that 5% denotes (fluoride makes up 45.45% of the weight of NaF).  In Advantage Arrest, 5% is free ionic fluoride, but it’s not adjusted for specific gravity.  When you do that mg/ml it works out to 44,800 ppm F.