Fifteen-day-old specific pathogen-free Sprague-Dawley (SD) rats are suitable for caries studies. The first and second molars are coming through at this age. Mutans streptococci are inoculated to animals during this period. If inoculation lags behind, the prevalence of dental caries is reduced (Ooshima et al, 1994). The number of mutans streptococci that must be inoculated to definitely cause dental caries is very important. The breeding period after inoculation with mutans streptococci is about 55 days. Diet #2000 is a popular diet in animal experiments on caries (Keyes and Jordan, 1964) and contains 56% sucrose. If the percentage of sucrose is reduced, the prevalence of dental caries is also reduced. Phytochemicals are commonly added to the diet to evaluate anticariogenic effects. After breeding, the molar is removed and the degree of dental caries is scored. The details of the experimental protocol have been described (Ooshima et al, 1981; Tsunehiro et al, 1997). The typical procedure of caries scoring is the Keyes Caries Score (Keyes, 1958).
According to the established method, we have carried out animal experiments using phytochemicals that revealed anticariogenic effects in vitro. Young rats were fed with diet #2000 containing phytochemicals with anticariogenic effects for 60 days. However, our results were inconclusive. Therefore, we would like to describe some key points for the planning of animal experiments based on our experience.
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