This study was designed to monitor fluorine concentration changes in the surface layer of enamel subjected to acid etching for orthodontic direct bonding. Prior to etching, the area described by the reference pins was partitioned into quadrants and initial fluorine concentration profiles in the surface 4
Although considerable variations in surface fluorine profiles were noted between teeth and within the same tooth, depletion of fluorine commenced with as little as 15 seconds of etching and plateaued off at between 0.1% to 0.2% after 120 seconds. Loss of enamel during the etching procedures also varied between teeth and between test quadrants but indicated minimal difference for 15, 30 or 60 seconds of etch (ranging from an average of 1.1
Etching times beyond 60 seconds eliminated the protective surface fluorine and risked significant loss of the enamel surface, indicating a 30-second to 60-second etch to be a good compromise for most clinical bonding situations.