How can Ad. Arrest be 44 800 pm and a NaF varnish 22 600 ppm, if it is the almost the same percentage fluoride?
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.