Caries-Promoting Properties of Fermented Milk Beverages Containing Live or Killed Lactobacillus

Abstract

This paper describes the effects of fermented milk beverages, “Yakult”containing live Lactobacilli (Abbreviation: LL beverage), and“Calpis”containing killed Lactobacilli (KL beverage), on caries in hamsters and rats.Golden hamsters of NIH strain and Sprague-Dawley rats were used in the experiment. Microflora normally harboured in the mouth of the rodents were suppressed by providing penicillin in drinking solution for a few days before the experiment started. The animals, uninfected or infected with Streptococcus niutans K1-R, were reared on cariogenic diet #2000 and the beverages or deionized water as drinking fluid for 42 to 60 days. The raw or heat (100°C, 15min.) -treated LL beverage was used at original concentration, and the raw KL beverage at 5-fold diluted concentration. The diet and drinking solutions were continuously available. Molar dentitions of hamsters and rats were scored for dental caries by Keyes' method and the modified Takei's method, respectively.Uninfected hamsters and rats produced almost negligible carious lesions, whereas oral infection of K1-R induced moderate caries in the rodents of control groups receiving deionizd water. When the animals were provided with raw or heat-treated LL beverage continuously for 60 days, caries extents of both uninfected and infected animals became much more severe compared with those of respective controls. Administration of KL beverage also induced severe caries in hamsters reared on the cariogenic diet for 42 days. The ability of both beverages to promote caries with various severities were also demonstrated by analyzing individually the caries scores of 3 molars of hamsters and 14 pit-and-fissures of rat's molars, which were shown to have various caries susceptibilities. The caries development of infected hamsters, however, were reduced to the extent of infected control by providing the beverages intermittently, 3 days and/or 1 day per week. These results clearly indicate that the continuous administration of the beverages promotes various types of caries with various severities in the rodents.In addition, continuous administration of the beverages induced erosion-like lesions on the enamel of molar dentitions, particularly on the occulusal surface of 1st molar. The lesions might be caused by the highly acidic property of the beverages.Experimental animals receiving LL beverage were significantly lower, but not the groups receiving KL beverage, than control animals in body weight gain and diet consumption.