Effects of fluoride, lithium, and strontium on growth and acid production of mutants streptococci and Actinomyces viscosus.

Eight strains of mutants streptococci and two strains of Actinomyces viscosus were studied to determine (1) their relative sensitivities to fluoride, lithium, and strontium and (2) whether lithium or strontium interact to enhance the known antimicrobial effects of fluoride. Analyses of variance of the data revealed a major inhibition of growth and acid production by fluoride, but not by lithium or strontium. Fluoride (5 mg/l) inhibited cell growth of all strains tested by a mean of 17% and total titratable acid production by a mean of 31%. However, there were marked differences between the strains. Mean total titratable acid was inhibited by fluoride least with the A. viscosus strains (15%) and most with the mutans streptococci (34%). Although interactions among the elements were statistically significant, they were generally slight in magnitude.

Acid reactivity of carbonated apatites with strontium and fluoride substitutions.

Carbonated apatites containing approximately 3.0 or 6.5% CO3 were precipitated in the presence of sodium, strontium, and/or fluoride at various concentrations. Almost all the available strontium and fluoride was incorporated into the crystals, whereas only a portion of the carbonate and sodium present was taken up. When incorporated together, Sr and F improved the crystallinity of carbonated apatites and markedly reduced their acid reactivity. This phenomenon may partially explain the observed reduction in caries for populations whose drinking water contains optimum levels of Sr at 5-10 mg/l and F at 1-2 mg/l.