PROTECTIVE EFFECT OF TOPICALLY APPLIED FLUORIDE IN RELATION TO FLUORIDE SENSITIVITY OF MUTANS STREPTOCOCCI

The aim of the present in vitro experiments was to determine whether t he protection of enamel by topically applied fluoride against deminera lization by bacterial acids would depend on the fluoride sensitivity o f the bacteria. Glucose-agarose gel suspensions of fluoride-sensitive and fluoride-resistant mutans streptococci were placed on bovine ename l specimens with different amounts of fluoride. One group of specimens was untreated, a second group had been pretreated with a F-lacquer, a nd a third group had been pretreated with the F-lacquer and rinsed sub sequently with a KOH-solution, to remove deposited CaF2. After 22-hour incubations at 37-degrees-C, the amounts of calcium and lactate and t he pH of the agarose gels were determined. This procedure was repeated on three consecutive days. Two parent S. mutans strains, one parent S . sobrinus strain, and five fluoride-resistant derivatives were tested . Both pretreatments gave a significant protection to the enamel speci mens. For the S. mutans strains, the degree of protection did not depe nd on the fluoride sensitivity of the strains. For the S. sobrinus str ains, the results suggested a reduced protection against demineralizat ion by the fluoride-resistant derivatives. Only from the second group of enamel specimens was enough fluoride released for inhibition of bac terial metabolism. Presumably, it was released by the dissolution of C aF2+. It is concluded that a possible adaptation of mutans streptococc i in dental plaque to frequent exposures to fluoride will not necessar ily decrease the caries-preventive effects caused by topically applied fluoride agents.