Journal of Dental Research, Vol 66, 1658-1662, Copyright © 1987 by International & American Associations for Dental Research Online Journals
Comparison of the effects of fluoride and the ionophore nigericin on acid production by Streptococcus mutans and the resultant in vitro enamel demineralization
C. Van Loveren, A. M. Fielmich and B. Ten Brink
Department of Preventive Dentistry, University of Utrecht, Utrecht, The Netherlands.
In an in vitro demineralization experiment with a plaque of S. mutans
C180-2 over enamel, the effect of 0.5 mmol fluoride/L was compared with
that of 10 nmol nigericin/L. Since the effects of both substances on the
acid production in a dense cell suspension were of the same magnitude, and
since nigericin did not affect the enamel solubility, the present
demineralization experiment may differentiate between the effect of
fluoride on bacterial metabolism alone and the combined effect of fluoride
on both the bacterial metabolism and enamel solubility. In our experiments,
the effect on bacterial metabolism accounted for 75% of the
caries-inhibiting effect of fluoride. Microradiographic data showed
subsurface lesions in the control and nigericin group and a slight
surface-softening in the fluoride group. In addition, the effects of
fluoride and nigericin on the cellular internal pH during glycolysis were
studied. Analysis of these data suggested that glycolysis was inhibited
when the intracellular pH reached about pH 5.2, which supports the view
that acidification of the cell cytoplasm is a mechanism by which fluoride
inhibits glycolysis.
