Conclusions
Introduction
The most important external modifying factors related to dental caries are frequent intake of fermentable carbohydrates and socioeconomic factors.
Dietary factors
The 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). The most precipitous fall in pH is induced by sucrose, closely followed by glucose, and fructose, while the effect of raw starch is negligible. Sucrose, glucose, and fructose are therefore considered to be highly cariogenic.
"Sugar" (sucrose) is used universally as a sweetener and an inexpensive source of energy. Excluding China and some other developing countries, the average annual consumption is about 50 kg per individual. In Sweden, for example, daily consumption has remained persistently high (about 120 g per individual) for 40 years, although the proportion of indirect consumption, in the form of drinks and sticky sweets, has doubled, increasing from about 30% to more than 60%. Nevertheless, during the same period, a dramatic decrease in caries has been achieved in Sweden.
Experimental studies have shown that, in germ-free animals, frequent intake of sugar does not result in caries (Orland et al, 1954). However, if cariogenic human bacteria (mutans streptococci) are inoculated into the mouth of one animal in a group being fed on fermentable carbohydrates, rampant caries develops in the whole group (Fitzgerald and Keyes, 1960). In other words, dental caries is an infectious, transmissible, but multifactorial disease. Frequent sugar intake is not an etiologic factor, but an external (environmental) modifying risk factor for development of
caries on tooth surfaces covered with cariogenic plaque.
Conflicting results are reported from the numerous cross-sectional human clinical studies investigating the correlation between sugar consumption and caries prevalence. Most of the early studies, conducted in populations with high caries prevalence, showed that high intake of sugar-containing products was a significant risk indicator for dental caries. In more recent studies, in populations where caries prevalence is low, because of high standards of oral hygiene and regular use of fluoride toothpaste (for example, in Scandinavia), little or no such correlation has
been found, because "clean teeth never decay," and caries prevalence (experience) expresses the cumulative caries incidence (increment), since eruption of the tooth.
A few human longitudinal interventional or observational studies have been designed to evaluate possible correlations between intake of sugar-containing products and caries incidence. Experimental interventional human studies have been carried out in the absence of plaque control and fluoride (Gustavsson et al, 1954; Scheinin and Makinen, 1975; von der Vehr et al, 1970). These early Scandinavian interventional studies in adults demonstrated the following:
1. In the absence of plaque control and fluoride, frequent intake of sugar-containing
products is a significant risk factor and prognostic risk factor for dental caries.
2. If sugar is substituted with nonfermentable sweeteners, a significant reduction in
caries may be achieved.
Recent longitudinal observations in children, however, have shown little or no
correlation between the intake of sugar-containing products and caries incidence.
Because there is a strong correlation between the in vivo fall in the pH of the plaque
and demineralization of the underlying tooth surface, the effect on plaque pH of
dietary products containing different fermentable carbohydrates has been investigated
extensively. The cariogenic outcome of falls in plaque pH is influenced, however, by
the concentrations of fluoride, calcium, and phosphate ions in the plaque fluids and by
the microbial composition of the plaque.
In vivo plaque pH measurements have shown the following:
1. Plaque pH after rinsing with a sucrose solution is related to plaque age and site. The
lowest values are recorded in the maxillary teeth and on the most central part of the
approximal surfaces of molars. The pH drops below 5 in interdental plaque more than
3 days old but not in less mature plaque. In a toothbrushing population, interdental
plaque more than 3 days old, if present at all, should be located only between molars
and premolars.
2. Of the fermentable carbohydrates, the lowest plaque pH is induced by sucrose,
closely followed by glucose, fructose, and maltose. The fall in pH associated with
lactose and cooked starch (to pH 5.5 to 6.0) is not as severe but is critical for initiation
of root caries.
3. Plaque pH is related to the sugar concentration. Rinsing with even a weak sucrose
solution (2.5% to 5.0%) results in a suboptimal pH drop (below 5) in interdental
plaque that is more than 3 days old. The optimal pH drop occurs with 10% sucrose
solution; concentrations greater than 10% do not further depress plaque pH. Many
dietary products, such as mustard, ketchup, salad dressing, soft drinks, and ice cream,
contain 8% to 13% sucrose. While it is therefore unrealistic to exclude all products
containing more than 2% sucrose, the daily number of intakes should be restricted.
4. Plaque pH is correlated not only to the sugar concentration of the product but also
to the consistency (texture) and the pattern of consumption. For example, eating
cheese directly after sugar-containing products will rapidly raise the plaque pH, in
contrast to pasty bananas or sugary desserts. A habit that could be recommended for
caries prevention is a combination of the Southern European custom of finishing a
meal with a cheese platter followed by the new Scandinavian recommendation of
using sugarless fluoride chewing gum after meals.
5. Neither caloric sugar substitutes (sorbitol, xylitol, lycasine, and sorbose) nor
noncaloric sugar substitutes (saccharin, cyclamate, aspartame, etc) induce critical falls
in plaque pH, even to levels critical for root caries development. While these are now
widely used as sweeteners in products frequently consumed between meals, it is
unrealistic, nutritionally and economically, to recommend sugar substitutes in food
consumed mainly at mealtimes.
Clinical cross-sectional studies, longitudinal interventional and observational studies
in humans, and animal experiments, as well as in vivo plaque pH measurements
indicate a synergistic cariogenic effect of dental plaque and fermentable
carbohydrates (particularly sucrose) on plaque-covered tooth surfaces.
Evaluation of dietary habits is important, particularly in caries-susceptible individuals.
Because caries is a multifactorial disease, dietary data complement clinical and case
history data used to compile the patient's riskprofile (see chapter 4). The most
common methods for evaluation of dietary habits in relation to dental caries are the
dietary history and the 24-hour recall. Emphasis is on the frequency of intake of
sticky, sugar-containing products, which prolong sugar clearance time.
Dietary recommendations for caries control, while emphasizing noncariogenic or lowcariogenic
food habits, should also meet nutritional requirements and
recommendations for general health: fortunately, a healthy diet is not cariogenic. The
diet recommended for diabetics is in general agreement with such recommendations:
a high intake of fresh vegetables and fruits, carbohydrate intake from starch instead of
sucrose, and a low intake of fat.
For caries prevention and control, there are five major dietary recommendations:
1. Breakfast should be a balanced composition of dairy products, grains, and fruits.
2. The total daily number of intakes, including snacks, should be limited to about four.
3. Sticky sugar-containing products, which prolong sugar clearance time, should be
eliminated. Sugarless sweets and soft drinks are available as substitutes.
4. Each meal should include fiber-rich products, which stimulate chewing and
salivary flow. Cheese is recommended at the end of the meal.
5. Certain caries-susceptible individuals, particularly subjects with reduced salivary
flow, should use sugarless fluoride chewing gum for 20 minutes after every meal.
In future, refinement of the intraoral wire telemetric and the microtouch methods for
in vivo plaque pH measurements is expected. This will allow a more systematic
classification of the cariogenicity of food, for example, a scoring system from 1 to 5.
Several years ago, a similar system for sweets, assessed by the intraoral wire
telemetric method, was introduced in Switzerland. For ethical reasons, human
interventional longitudinal clinical studies are no longer allowed. Therefore, in vivo
plaque pH measurement is the only available method for evaluation of cariogenicity
of dietary products in humans.
Further improvements may also be expected in sugar substitutes, noncaloric as well as
caloric, with respect to taste and side effects. Use of such sweeteners will become
more widespread in snack foods such as sweets, confectionery, and soft drinks.
A concerted effort should be made to prevent infants from acquiring a taste for sweet
foods. Animal experiments have shown that, by frequent intake of sucrose during
pregnancy, a sweet taste can be acquired prenatally. The studies by Wendt and
Birkhed (1996) clearly showed that bottle-feeding of sweet drinks, particularly at
night, resulted in significantly increased caries development from the age of 1 to 3
years.
Finally, how do international experts perceive the past and present relationship
between dietary sugar and dental caries? Bratthall et al (1996), in a recent
questionnaire, sought the opinions of 55 international experts on dental caries and
preventive dentistry as to the main reasons for the caries decline in many Western
countries during the last three decades, specifically in 20 to 25 year olds. The
respondents were asked to rank reduced sugar consumption, reduced sugar frequency,
fluoride toothpaste, school fluoride programs, reduced amount of plaque, and fissure
sealants. The respondents ranked these in the following order:
1. Fluoride toothpaste
2. Reduced amount of plaque
3. School fluoride programs
4. Reduced sugar frequency
5. Fissure sealants
6. Reduced sugar consumption
However, it should be noted that fewer than 10% of people worldwide use fluoride
toothpaste, and the Western industrialized countries represent 30% to 40% of the
world's population. In addition, fewer than 1% of school-aged children worldwide
have access to school-based fluoride programs.
