Basic study on experimental rat caries. Serial observations of caries incidence and bacterial variation on rat molars in short-term experimental caries.

Abstract

A short-term rat experiment was carried out in order to investigate the time course of the incidence of rat molar caries and the variation in the number of the oral cariogenic microorganisms or their biochemical properties. From the results obtained, an attempt was made to clarify the oral environment at the time of incidence of initial caries.In the time course of the caries incidence, carious lesions appeared as soon as rat were introduced to a sucrose diet and increased quickly. At day 15, carious lesions were found in about 80% of all the fissures. Moreover, the rate of caries incidence was unchanged for the first 6 days. According to the caries score, the mean number of carious lesions of the rat group which were fed a non-sucrose diet was lower than that of the experimental group, so that a difference in caries incidence was seen even in short-term experiments.As to the bacteria existing in the teeth, according to the incidence of the initial fissure caries, variation in the quantity of some microorganisms occured. Regarding S. mutans, the isolation rate and the number were not lower in the rats fed a non-sucrose diet than in the rats fed a sucrose diet.In biochemical tests, the strains of S. mutans derived from sucrose diet group strongly fermented sucrose, while a strain from the non-sucrose diet group had lower final acidities from glucose or starch than those of sucrose.From these aspects, regarding the incidence and progress of incipient caries, I suggest that biochemical factors of the various bacteria have stronger influence than their mere numbers, and it seems likely that the oral environmental factors, especially sucrose, have an important effect upon the biochemical behavior of oral microorganisms, and then the biochemical properties are changed to cariogenic. I believe that the early establishment and evaluation of oral environment factors such as diet and microorganisms are very important in caries prevention.