After exposure of dental plaque to fermentable carbohydrates, the pH decreases rapidly. This is due primarily to the production of lactic acid in plaque, with acetic and propionic acids being simultaneously lost from the plaque.6,10 The rate at which the pH decreases is due in part to the microbial composition of dental plaque. In general, if more acidogenic, aciduric bacteria is present in plaque, the pH would lower more rapidly. The rate of pH decrease is also dependent on the speed with which plaque bacteria are able to metabolize the dietary carbohydrate. While sucrose would be metabolized quickly, prompting a more rapid decrease, larger molecules, like starch, would diffuse into plaque more slowly because it would need to be broken down before it can be assimilated by plaque microbes.6 Another factor that affects the rate of pH decrease is the buffering capacity of unstimulated saliva.6,11 The rate at which plaque pH decreases is also influenced by the density of plaque. Less dense plaque can be penetrated more easily by buffering saliva and oxygen causing slower pH decreases than very dense plaque, which cannot be accessed by saliva and oxygen.6,12
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