The patients were subjected to four treatment protocols involving acidulated phosphate fluoride ( APF ) application followed by rinsing the mouth with water : ( @ ) after @ minutes ( APF-@ ) ; ( @ ) after @ minutes ( APF-@ ) ; ( @ ) immediately ( APF-@ ) ; after cleansing the teeth with a cotton roll immediately following APF ( APF-cotton ) ; or ( @ ) no fluoride therapy ( control ) .