ConclusionsIntroductionThe most important external modifying factors related to dental caries are frequent intake of fermentable carbohydrates and socioeconomic factors.  Dietary factorsThe fermentable carbohydrates may be ranked in order of complexity, as monosaccharides (glucose and fructose), disaccharides (sucrose, maltose, and lactose), polysaccharides (glucan, fructan, and mutan) and starch.  If there is undisturbed cariogenic plaque on an accessible tooth surface, intake of any of the fermentable carbohydrates will result in a drop in pH in the plaque and on the underlying tooth surface, where some demineralization may occur (see Fig 2).

Influence of social and behavioral variablesAs discussed earlier in this chapter, the development of dental caries is a complex interaction of etiologic factors and many modifying risk and protective factors. Social factors influence behavior directly related to dental caries, such as oral hygiene, dietary habits, and dental care habits. Besides the influence of social and sociobehavioral factors on, and interaction with, sugar intake, one behavior in particular influences the caries-promoting effect of sugar intake, namely oral hygiene.

Influence of socioeconomic statusSocial classThe relationship between parents' social status and children's dental health has been demonstrated in numerous studies. Many studies in Western industrialized countries have also shown a relationship between on the one hand, the parents' dental health status, dental knowledge, and dental care habits and on the other, the prevalence and incidence of dental caries in their children (Martinsson, 1973; Martinsson and Petersson, 1972).

Role of Socioeconomic and Behavioral FactorsIntroductionAt group and population level, socioeconomic factors, particularly educational levels, are emerging as the most important external factors related to dental caries today. History has clearly shown a relationship between social characteristics and dental disease patterns and, in particular, how social changes have influenced those patterns.  Wartime, urbanization, and industrialization, to mention a few, have affected caries prevalence.

Influence of other risk factors on diet-related cariesCertain conditions may predispose people to risk for diet-related dental caries. Systemic diseases and regular medication may affect caries risk. The disease or medication per se might increase caries risk, but sometimes the increased risk is related to treatment. The increased need for energy and nutrients during a disease episode is often not met, and the patient may be undernourished. Intake of medicines containing sucrose must be noted, eg, fiber supplements for constipation, cough mixtures, and antibiotics.

Dietary recommendations for general health promotionGeneral recommendationsGeneral guidelines for energy and nutrient intake are given in the Nordic recommendations from 1989, and in recommendations specific for each Scandinavian country. They give age- and sex-specific recommendations for daily energy and nutrient intake as well as minimal daily required amounts for healthy individuals older than 3 years. It is recommended that energy intake be at a level that does not cause obesity and that there be five or six daily intakes of food at even intervals throughout the day.

Evaluation of dietary factorsThe human longitudinal studies described earlier showed that, in individuals with little or no plaque control and no use of fluoride, frequent intake of sugar-containing products is a significant risk factor or prognostic risk factor for dental caries. In addition, in vivo plaque pH measurements have shown that the drop in pH and sugar clearance time in undisturbed plaque (more than 2 days old) is related to the sugar concentration and consistency of the food item being evaluated (see Figs 63, 64, 65, 66, 67, 68, and 69).

Influence of hydrogen ion concentration (pH) of plaque  It is generally accepted that enamel caries is the result of a disturbance in the equilibrium between enamel hydroxyapatite and the calcium and phosphate ion concentrations of the dental plaque covering the enamel surface. At neutral pH, plaque seems to be supersaturated with these ions. A fall in pH, however, caused by intraplaque bacterial fermentation of carbohydrates, leads to a shift in the equilibrium of concentrations and to dissolution of enamel.

Evidence from human longitudinal, interventional, and experimental studies There are many reasons why there are so few planned interventional human studies of diet and dental caries¾for example, the problem of persuading groups of people to maintain rigid dietary regimens for long periods of time. Although most of such studies involved providing daily sugar supplements to subjects¾a practice that would be considered unethical today¾these studies made an important contribution to dental knowledge.

Evidence from cross-sectional studiesNumerous cross-sectional observational studies in children have used dietary  interview and questionnaire methods to study the relationship between caries prevalence and consumption of sugar and sweets. The results are somewhat conflicting (Rugg-Gunn, 1989): A significant, but not very strong, correlation between caries and the total quantity of sugar consumed has been found in some studies but not in others. A closer relationship has been demonstrated between caries and the quantities of sweets and confectionery consumed, probably because these products are consumed in ways that enhance cariogenicity¾between meals and over long periods¾whereas consumption of even large quantities of sugar at meals seems to do little harm.

Evidence from epidemiologic studiesNumerous worldwide epidemiologic studies during the 20th century have shown thatcaries prevalence is low in developing countries or populations living on a local,carbohydrate-rich diet, based on starch instead of sucrose. Figure 51 shows sugarconsumption in 1977 in a number of countries worldwide. Consumption is extremelylow in China, and caries prevalence among 12 year olds is very low. On the otherhand, sugar consumption in Japan is only about half that of other industrializedcountries, but caries prevalence is moderate to high.

Role of fermentable carbohydrates (sugar and starch)A diet rich in fermentable carbohydrates (frequent sugar intake) is indisputably a verypowerful external RF and PRF for dental caries in populations with poor oral hygienehabits and an associated lack of regular topical fluoride exposure from toothpaste.However, in populations with good oral hygiene and daily use of fluoride toothpaste,sugar is a very weak RF and PRF, because clean teeth never decay, and fluoride is aunique preventive factor. The biochemical role of fermentable carbohydrates such assucrose in the development of an enamel caries lesion on a plaque-covered toothsurface is illustrated in Fig 2 (see chapter 1).

External Modifying Factors Involved in Dental CariesIntroductionAwareness of the multifactorial nature of dental caries is of fundamental importance.Figure 48 illustrates the interdependence of most of the determinate variablesassociated with dental caries. Besides etiologic, preventive, and control factors, manyother factors may modify the prevalence, onset, and progression of dental caries. Suchfactors may be divided into external (environmental) and internal (endogenous)factors (to be discussed in chapter 3).

Prediction and prevention of cariesThe younger the population and the lower the caries prevalence in the population, thehigher the percentage of caries-free subjects. In these populations, it is necessary tofocus on "high-risk strategy" and primary prevention, rather than secondaryprevention.For practicing primary prevention according to the high-risk strategy, the etiologicfactors used for caries prediction must be as sensitive as possible, that is, optimizingthe percentage of true high-risk individuals for cost effectiveness.

Rationale for combining salivary MS tests and PFRI for prediction of caries risk Like the inflammation induced in gingival soft tissues adjacent to dental plaque, carious lesions that develop on the individual enamel surface beneath bacterial plaque should be regarded as the net result of an extraordinarily complex interplay between harmless and harmful bacteria, antagonistic and synergistic bacterial species, their metabolic products, and their interaction with the many other external (fermentable carbohydrates etc) and internal (saliva and other host factors) modifying factors,which are discussed in more detail in chapters 2 and 3.

Selection of caries-risk patientsInability of a sole salivary MS test to predict caries riskAs already mentioned in this chapter, numerous cross-sectional as well as longitudinalstudies have shown significant correlations between salivary MS levels and cariesprevalence and caries incidence (for review, see Bratthall, 1991; Bratthall andEricsson, 1994; Beighton et al, 1989). At the surface level, even more significantcorrelations between MS colonization and caries incidence have been found(Axelsson et al, 1987b; Kristoffersson et al, 1985).

Accuracy ofrisk assessments in practiceA perfectrisk marker would have a sensitivity of 100% and a specificity of 100%, implying noerrors in risk assessment. Consequently, the false-positive and falsenegative rates wouldbe 0%, and positive and negative predictive values would be 100%.Having perfect accuracy means that the predicted high-risk group would consist ofonly true high-risk individuals and that only true low-risk individuals would be includedin the predicted low-risk group.

Prediction of Caries RiskPrinciples of risk predictionSome basic principles have to be followed for successful and cost-effective cariesprediction, caries prevention, and caries control:1. The higher the risk of developing caries for most of the population, the moresignificant the effects of one single preventive measure and the stronger thecorrelations between one single etiologic or modifying risk factor and the risk forcaries development.2. In populations in which only a minority of the people will develop new cariouslesions, it is necessary to use accurate risk predictive measures to select at-riskindividuals and introduce needs-related combinations of caries-preventive measures,in other words, a "high-risk strategy.

Cariogenicity of other bacteriaThere are overwhelming data from experimental and clinical studies in humans showing that S mutans and S sobrinus and lactobacilli are strongly correlated to caries etiology. However, the use of selective substrates in most of these studies may have introduced some bias. For example, Sansone et al (1993) found that plaque samples with and without MS and lactobacilli were equally acidogenic when cultured at low pH and in the presence of excess glucose.

EvidenceLactobacillus counts have been used to predict the incidence of new carious lesions. Crossner (1981) studied a group of children, who had been given dental treatment at baseline so that no open lesions were present at the bacterial sampling. Two subgroups in this material are of special interest: those with very low or very high lactobacillus counts. Very few individuals in the low lactobacillus group developed new carious lesions over a 64-week period. In the high lactobacillus group, many, but not all, developed new lesions.