Comparative effect of SnF2, NaF, and SnCl2 on the growth of Streptococcus mutans

The inhibitory effects of NaF, SnF2, and SnCl2 were compared in vitro on the growth of Streptococcus mutans NCTC No. 10449. Sodium fluoride arrested growth at 300 and 600 ppm F (while SnF2 suppressed the rate of growth at 75 ppm F), showed some bactericidal activity at 150 and 300 ppm F, and was totally bactericidal at 600 ppm F. The greater inhibition by SnF2 suggests an additive effect of SN2+. As a measure of a fluoride-free Sn2+ solution, SnCl2 was inappropriate since most of the tin present, at a neutral pH, was Sn4+. The influence of pH was particularly noteworthy with SnF2 at 600 ppm F, where a total bactericidal effect was observed within four h at pH 5.9, while viable cells were still recoverable from four to 40 h with SnF2 at pH 7.2.