Fluoride varnish is a protective coating that is painted on teeth with a brush. Over a period of time, the varnish releases fluoride which strengthens teeth. Benefits of fluoride include more resistant teeth to carious decay and less decay causing microorganism in the mouth. Fluoride ions fill the voids in the calcium hydroxy apaptite lattice structure which forms the outer covering of the tooth. in short it helps your teeth to become stronger and more resistant to caries thus preventing dental decay.