<prompt> The best sustaining topical effect of fluoride is obtained by:NaFAPF gelDuraphatSnF  <response>: Duraphat, the first fluoride varnish developed in Germany, is a viscous yellowish material, containing 22,600 ppm fluoride as sodium fluoride in a neutral colophonium base NaF varnish containing 2.26 fluoride in organic lacquerNaF- 9200 ppmSnF2 - 9500 ppmAPF- 12300 ppmEssentials of preventive and community dentistry 5th editionSoben Peter page no. 256 