The starvation effect:
The bacteria that cause cavities can't metabolize xylitol.
(You may find that you want to read our brief outline describing
how cavities form before reading on.)
When xylitol (a five carbon sugar alcohol) is present in the oral environment cariogenic bacteria (the bacteria that cause tooth decay) transport it through their cellular walls via an uptake system intended for the purpose of importing fructose (a five carbon sugar). During this transport process the xylitol molecule gets transformed into xylitol phosphate, a compound, as it happens, that these bacteria cannot metabolize.
Over time, as the level of non-metabolized xylitol phosphate accumulates within the bacteria, it has the effect of becoming toxic to them. This is because xylitol phosphate interferes with metabolic pathways that these bacteria rely upon for their nourishment.
This means then that the effect of the presence of xylitol in the oral environment is to
create a situation where at minimum cavity forming bacteria become "starved," or at the extreme, die. Both of these scenarios create a situation where the growth and well being of the population of cariogenic bacteria is impaired.
Of course, a decrease in numbers of cariogenic bacteria that live in dental plaque will correlate with an overall decreased level of acidic byproduct formation from the metabolism of dietary sugars.
As a result, the overall acidity of the dental plaque will be less, thus helping to maintain
an environment where tooth demineralization (tooth decay formation) is less likely to occur.
The xylitol induced population shift:
The presence of xylitol favors the growth of less virulent strains of cariogenic bacteria.
(You may find that you want to read our brief outline describing
how cavities form before reading on.)
The long-term presence of xylitol in the oral environment creates an effect on the
cariogenic bacteria that live in dental plaque. Within this population of bacteria there will be some bacterium that have an altered fructose uptake system (one which xylitol cannot participate in). Because of this, these bacteria will not accumulate toxic levels of xylitol phosphate.
This means that, in the presence of a long-term exposure to xylitol, these "xylitol-resistant" bacteria will continue to thrive whereas their "xylitol-sensitive" counterparts will not.
The net effect is that there will be an on going naturally occurring selection process that favors the xylitol-resistant strains. Over time, the numbers of xylitol-sensitive bacteria will diminish and the numbers of xylitol-resistant strains will grow and ultimately predominate.
Research has suggested that xylitol-resistant strains of cariogenic bacteria are less virulent
(less capable of creating tooth decay) than their xylitol-sensitive counterparts. It is unknown precisely why this is the case. One theory suggests that xylitol-resistant bacteria have impaired adhesive properties.
The ability of cariogenic bacteria to cause tooth decay depends, in part, on their ability to adhere to its surface.
Since the xylitol-resistant forms of cariogenic bacteria cannot tightly grip to the surface of teeth,
their ability to create conditions right for tooth demineralization is significantly diminished.
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