Acidogenic bacteria metabolize (ferment) simple sugars (glucose, fructose, sucrose, lactose, and maltose) to acids. Sugars may be present as a result of their direct consumption or as a result of the enzymatic breakdown of starches within the mouth by salivary amylase. Thus, a substantial proportion of a typical diet will contain a source of fermentable carbohydrate, and many, if not all, eating and drinking occasions will give these bacteria one of these metabolic precursors. The more frequently an individual consumes carbohydrate, the more the acido-genic bacteria thrive and other, less acid tolerant, bacteria are disadvantaged.
A wide variety of foods contain carbohydrate that is capable of giving rise to acids as a result of bacterial metabolism (fermentation) within dental plaque. Of the common dietary sugars, sucrose, fructose, and glucose are found in fruit and fruit juices, soft drinks, jams, honey, chocolate and other confectionary, and an immense variety of composite foods and drinks. Lactose arises naturally in milk and milk products but is also widely used as an ingredient in its own right by the food industry.
Starches are also classed as fermentable carbohydrates because they are partially broken down by amylase in saliva during chewing to maltose and glucose. Residues of starchy foods are frequently caught between the teeth and in the fissures of the molar teeth, where they may be broken down to sugars over long periods. Measurements of the pH of plaque following the ingestion of starches have suggested that the depression of pH may be as great as and last even longer than that produced by some sources of sugars, such as drinks, because of slow clearance. Highly processed starchy products, such as heat- and pressure-processed extruded snacks, are likely to be more readily converted to sugars than less processed starchy foods, such as bread.
Clearly, the wide range of individual dietary choices and eating habits may influence the risk of developing caries. The physical characteristics of fermentable carbohydrates will affect the rate at which they are cleared from specific sites in the dentition. Foods that are inclined to remain for long periods in stagnation sites (for example, between the teeth), such as toffees or raisins, are likely to give rise to a greater local fall in pH than are those that are rapidly cleared, such as chocolate. Clearance rates are also influenced by the increase in salivary flow that is stimulated by eating or drinking. When salivary flow is greater, for example after consuming a strongly flavored food, clearance will be faster and demineralization is likely to be less than that after consuming a bland food.
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