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products were only moderately cariogenic by comparison with sugar. More recently, Grenby and Mistry (16) reported that caries scores in rats were nearly 30% higher in animals fed plain (dark) chocolate rather than those on a milk chocolate regimen.
Food Retention, Acid Production and Enamel Dissolution
This method measures the amount of a food retained in the mouth after eating (clearance time), the amount of acid inherent in a food (or produced by incubation with saliva) or the amount of human enamel dissolved per unit time when enamel is incubated with a slurry of food and saliva. These measures have been used to assess cariogenicity, since a food that is retained in the mouth for a long time provides a substrate for bacteria to produce acid, which will be more likely to dissolve human tooth enamel.
The early studies by Bibby and Mundorff (17) showed that chocolate products, particularly those containing added ingredients such as nuts, etc., cleared from the mouth quickly. When the foods used in the Vipeholm Study (6) were compared for rates of clearance (Fig. 13.1), it can be seen that the chocolate group of subjects recorded lower clearance times than the toffee and caramel groups in which the higher caries occurred. Chocolate would therefore be classified as a low cariogenic food, as its lower rate of retention would give less opportunity for oral bacteria to ferment and produce less amounts of acid.
Studies by Bibby and Mundorff (17) have shown that tooth enamel lost to acid dissolution is not related to acid formed (Table 13.3). Some foods have low acid but dissolve enamel, such as white flour, while others, such as milk chocolate, have a high acid formation but dissolve little enamel.
Foods may have a varying degree of inherent acidity and therefore may also be more or less conducive to acid production by oral cariogenic bacteria. The amount of acid produced intra-orally can be measured and used as yet another
Table 13.3 Acid formation and enamel dissolution by some foods and candies.
Wholewheat bread White bread White flour Graham flour Cornflakes All Bran, cereal Chocolate coconut bar Milk chocolate
Source: after Bibby and Mundorff (17).
Acid formed (0.05 M NaOH ml)
Enamel dissolved (mg x 10)
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indicator of cariogenicity. However, just because a food is acidogenic does not mean that tooth enamel is attacked in a direct relationship to the quantity of acid produced. This is because there may be other components in the food that buffer any acid produced. Milk products, as noted above, calcium caseinate and other ingredients may have such a buffering effect. The lower CPI of milk chocolate, noted by Grenby and Mistry (16) may be explained by this.
Stralfors (18) showed that various fractions of cocoa had an inhibitory effect on dental caries in hamsters. In vitro observations made by Ferguson and Jenkins (19) also showed that extracts of commercial cocoa had a marked effect in reducing acid solubility of tricalcium phosphate, similar to enamel. Later, s'Gravenmade and Jenkins (20), also using in vitro tests, indicated that there is a cariostatic agent in cocoa. The moderate CPI of chocolate may also be explained, therefore, by an inherent cariostatic effect of cocoa used in the manufacture of chocolate.
Although chocolate has been associated in the lay public's mind, as well as within much of the dental profession, with the promotion of dental caries, the experimental evidence for such an association is thin. The limited human studies have shown chocolate to have only a moderate cariogenic potential which has been confirmed in a number of animal experiments. Studies on the effects of chocolate and chocolate products on intra-oral plaque pH measurements also indicate that chocolate is only moderately related to acidogenicity. The moderate cariogenicity of chocolate is probably related to the cocoa fraction of chocolate, which contains chemicals inhibitory to oral bacteria. In addition, added ingredients such as nuts may reduce the clearance time and will therefore render the products even less potentially cariogenic. As chocolate also usually includes dairy products, which are cariostatic, milk chocolate in particular has further protection.
Whilst not entirely free of a cariogenic potential, chocolate when used in moderation should not be considered as playing a major role in the aetiology of dental caries. Chocolate, however, is not always eaten as chocolate but more often as a chocolate bar with other ingredients. Some of these combinations may be more or less cariogenic, but the detailed research has yet to be carried out to determine which is which. Such research would be valuable in formulating chocolate bars with a low-to-moderate cariogenic potential that could be recommended as part of a dental caries preventive programme.
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