The effects of fluoride concentration and the level of cariogenic challenge on caries development in desalivated rats

Dental caries is an infectious and transmissible disease that continues to affect the majority of people. The presence of carbohydrate, mainly sucrose in the diet, is an important factor in its occurrence. The amount of fluor ide required for optimal protective effect where there is a high caries cha llenge is unclear. Differences in the intensity of cariogenic challenge, fo r whatever reason, may play a part in determining fluctuations in the effec tiveness of fluoride. The purpose of this study was to evaluate the effect of different concentrations of fluoride on the development of caries and ex plore the cariostatic effect of fluoride under various levels of cariogenic challenge. The study comprises two experiments. In experiment I, 60 desali vated Sprague-Dawley rats infected with Streptococcus sobrinus were offered the following to drink for 21 days: group (1), sterile distilled water (SD W); (2) 10 parts/10(6) F SDW; (3) 20 parts/10(6) F SDW; (4) 30 parts/10(6) F SDW; (5) 40 parts/10(6) F SDW. In experiment II, eight groups of 9 rats w ere placed in a Konig-Hofer programmed feeder and were exposed to different levels of cariogenic challenge through varying frequency of eating and off ered water containing 10 parts/10(6) F. In experiment I, exposure to 20, 30 and 40 parts/10(6) F reduced caries development significantly: fluoride, a t 10 parts/10(6), reduced the severity of the carious lesions. In this mode l of severe cariogenic challenge, the results suggest that elevated concent rations of fluoride might be effective in patients at high caries risk. In experiment II, fluoride reduced the incidence and severity of smooth-surfac e caries in all groups. The protective effect of fluoride decreased as the number of exposures to sugar increased. It is concluded that the effectiven ess of fluoride is influenced by the level of cariogenic challenge and that consideration should be given to adjusting the level of fluoride exposure based on perceived caries risk, and that there is a maximum therapeutic eff ect of fluoride beyond which no additional protection can be expected. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.