The potassium/calcium ratio of saliva bears no apparent relationship to susceptibility or immunity to caries. When this K/Ca ratio is correlated with that of blood, no relationship for caries susceptibility or immunity is indicated. A method for determining susceptibility or immunity to caries may be conducted as follows : Add to 3 cc. of saliva, 0.3 cc. of 1 percent aqueous solution of glucose. After incubation for four hours, the acidity will equal pH 5, if the saliva is from a person having active caries. Six hours of incubation are required to produce this degree of acidity by saliva from a person only slightly susceptible to caries. This degree of acidity is not produced, in any period of incubation, by saliva from a person immune to caries. The rate and degree of acid production depend upon the number and fermentative activity of acidogenic bacteria in the saliva, the number and activity being greatest in saliva from persons having active caries.
References: J. Den. Res., 1936; Studies of the relationships between various salivary constituents and dental caries, M.S. thesis, University of Illinois, 1938.