Xylitol: a review of its action on mutans
streptococci and dental plaque--its clinical significance.
Int Dent J 1995 Feb 45:1 Suppl 1 77-92
Abstract
Many mechanisms have been proposed to explain the caries
preventive effect of xylitol as a total or partial dietary sugar
substitute. This article reviews the current knowledge of the
effect of xylitol on the microbial population of dental plaque,
particularly on mutans streptococci, in the light of an
ecological concept of the oral environment and of the potential
clinical significance. A noncariogenic commensal plaque flora
constitutes the biotic component of a balanced ecosystem
compatible with dental health. Dietary sugars, particularly
sucrose, and sugar substitutes are abiotic environmental factors
that can shift the delicate balance of the ecosystem towards a
more or less cariogenic microbiota. Most dietary sugars are
fermented by plaque microorganisms, favour the establishment of a
cariogenic microflora and contribute to bacterial virulence. The
vast majority of plaque bacteria, however, are incapable of
fermenting xylitol into cariogenic acid end-products. There is no
evidence that the plaque microbiota can adapt to metabolise
xylitol or can be enriched with xylitol-metabolising cells even
after long exposure to xylitol. Accumulated intracellularly as a
non-metabolisable metabolite by mutans streptococci, xylitol
inhibits its growth in vitro and reduces the amount of plaque and
the number of mutans streptococci in both the plaque and saliva
of xylitol consumers. When present in the oral environment
xylitol not only prevents a shift of the bacterial community
towards a more cariogenic microflora but also selects for a
mutants population that was shown to have weakened virulence
factors in preliminary in vitro experiments and in rats. Further
research is needed to fully understand the clinical importance in
the prevention of caries of this xylitol-selected population.