Residual Anticaries Effect of Topical Sodium Fluoride Applications in the Syrian Hamster

Two experiments with the Syrian hamster were conducted to estimate the degree of residual anticaries effect remaining after a series of daily, 2-minute, topical sodium fluoride applications had been discontinued. The residual protective effect of topical fluoride was assayed in the maxillary second and third molars, which are ordinarily highly vulnerable to dental caries under proper laboratory conditions. The hamster maxillary second molar erupts when the animal is about 14 days old, whereas the maxillary third molar first appears in the mouth at about 35 days of age. Because of this long interval between the eruption of the second and third molars (approximately 21 days), it is possible to apply fluoride selectively to the second molar but not to the third molar. Daily applications may be repeated until the third molar erupts and then discontinued. Afterward, hamsters can be observed for a period of time to determine whether plaque will form, whether enamel demineralization will eventually develop in the second molar, and whether the expected amount of severe cavitation will occur in the third molar. Dental caries may also be allowed to begin in the second molars of weanlings for 2 or 3 weeks, and the repeated daily topical fluoride applications may be started immediately after the third molar erupts. Such applications may be stopped after a given time and the hamsters observed to determine any residual protective effect against caries activity in the third molar. Materials and Methods