Acidogenic bacteria in dental plaque rapidly metabolize fermentable carbohydrates producing acidic end products. In the mouth, these changes over time in response to a challenge (usually a cariogenic food) are known as Stephan responses or Stephan curves.8 The pH of dental plaque under resting conditions (i.e., when no food or drink has been consumed), is fairly constant. Differences do exist, however, between individuals and in different sites within an individual.
The response after exposure of dental plaque to a fermentable carbohydrate is that pH decreases rapidly, reaching a minimum in approximately 5 to 20 minutes. This is followed by a gradual recovery to its starting value, usually over 30 to 60 minutes, although this can be longer in some individuals.
The significance of a Stephan curve shows that the plaque pH curve will drop a lot and quickly after the consumption of fermentable carbohydrates. And then it will drop below what we call a critical pH, in which case the demineralization of the tooth enamel minerals will occur. And that actually takes quite a long time for the plaque pH to slowly climb up and return back to the resting, habitual level. That means that over a period of time, demineralization will occur. And the more frequent the consumption of the carbohydrate intake, it means that the longer the time period for the demineralization to occur. In terms of prevention, the most important part is that we need to make sure that our patients do not consume fermentable carbohydrates at a high frequency. And then we try to promote remineralization, in that case make sure that it does not fall below the critical pH for a long time.
The following sections discuss some of the mechanisms underlying each stage of the Stephan curve: