Bacteriological Studies of the Effects of Cow's Milk on Dental Plaque and Dental Caries in Rats

The effects of liquid milk and skim milk powder on the bacterial composition of rat dental plaque and dental caries were examined in two separate experiments. First, groups of rats fed a cariogenic diet plus one or other of three types of liquid milk had. after 28 d. similar plaque flora. Those rats receiving reconstituted spray-dried skim milk had a significantly higher incidence of dental caries than those receiving either pasteurized and homogenized milk or ultra-heat treated milk. The differences in caries scores may be related to differences in inorganic phosphate and calcium levels of the milks. Secondly, rats fed a diet containing 65% phosphate-free sucrose plus 32% spray-dried skim milk in powder form had a significantly lower dental caries score than did rats receiving a diet containing 65% sucrose plus 32% autoclaved roller-dried skim milk powder. At the end of this experiment, the plaque flora had changed significantly and the difference in caries incidence was related to the reduction in the percentage of potentially cariogenic bacteria.
These results indicate that the mechanism by which milk reduces dental caries incidence may be (a) by remineralizing incipient carious lesions or (b) by mediating changes in the bacterial composition of dental plaque.