Evaluation of the Colorimetric (Snyder) Test

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Abstract
An evaluation of the colorimetric (Snyder) test for the estimation of numbers of lactobacilli in the saliva was made with specimens of saliva routinely submitted for culture. In a series of 2016 specimens the incidence of positive color change increased in respect to time and numbers of lactobacilli but there was no absolute correlation; that is, there were a few exceptions at the extremes of negative counts and positive color change in 24 hrs. and high counts with negative color change in 72 hrs. In respect to an arbitrary limit of 10,000 lactobacilli/ ml. saliva, 2.4% of specimens containing less than this number gave positive color reactions in 24 hrs. compared with 33.4% with counts higher than this level. The percentages of positive color change in 48 hrs. were 28.5 and 90%, respectively. On the basis of precious studies which show a high degree of correlation between the incidence and rate of color change and caries activity and that the positive color reactions in 48 hrs. for the most part are caused by lactobacilli, it was postulated that the practicing dentist should be able to determine caries activity by this test as follows: consistently positive color reactions in 24 hrs., should be indicative of marked caries susceptibility; consistently negative tests in 48 hrs. should indicate slight or negative activity. The change in clinical status should also be reflected by the difference in rate of change and should be helpful in the measurement of therapy of any kind.