Suggestions are given as to the means whereby the professional application of topical fluoride solutions at the mixed dentition stage can be rationalized. One requirement is that the objective of such therapy be clearly understood. Whilst the prevention of new caries lesions is an obvious aim, the importance of slowing or arresting existing early lesions should be appreciated. Data from clinical studies indicate that topical treatments should be directed at newly erupted teeth concentrating on sites with the highest caries susceptibility. At the mixed dentition stage much of the preventive effort must of necessity be directed at pits and fissures in permanent first molar teeth. A prolonged fluoride application (PFA) method provides one means of treating these sites in partially or fully erupted teeth.