Final pH from Sugar Fermentation by Plaque Bacteria Isolated from Caries-free and Caries-active Individuals after Frequent Sugar and Urea Rinses

The purpose of this pilot study was to assess the hypothesis that adaptation of the dental plaque to acid and alkaline respectively, could differently affect the in vitro acid formation from sugars by acid tolerant plaque bacteria isolated from Caries-free (CF) and Caries-active (CA) individuals. 128 bacterial isolates growing at pH 5.2 were obtained from 10 CF and 10 CA individuals before and after one-week daily rinses 5 times/day with 10% sucrose and 0.25% urea solutions, respectively. The isolates were phenotypically identified and used in a microtiter plate assay to assess pH to the intervals <5, 5-6 and >6 after bacterial fermentation of sucrose, glucose, fructose and lactose. Both before and after the rinsing periods, nonmutans streptococci Streptococcus mitis and Streptococcus oralis characterized the CF group while S. mitis together with lactobacilli were the most frequently found in the CA group. The proportion of isolates forming acid from the sugars to pH <5 was to the highest extent increased in the CF group after the sugar rinses and decreased in the CA group after urea rinses (although not statistically significant). These findings conform to the general contention that plaque bacteria in caries active individuals are adapted to aciduric environments and therefore had a higher ability to form acid and protective ammonia as of commencement than those in the caries free individuals. This pattern was consistent for the four sugars but it needs a higher statistical power to prove the statistical significance for each of the sugars.