Dental caries develops by the localized dissolution of the tooth hard tissues, caused by acids that are produced by bacteria in the biofilms (dental plaque) on the teeth and eventually lead to "cavities." The biofilm consists of microorganisms, including the highly cariogenic mutans streptococci, and a matrix made up mainly of extracellular polysaccharides. The destructive acids are produced when fermentable carbohydrates (sugars) reach these biofilms, each episode resulting in tooth damage (attack). If this process does not occur frequently, then the natural capacity of the body (through saliva) to remineralize will prevent formation of a cavity. Thus, the main risk factors include presence of cariogenic biofilms and frequent consumption of fermentable carbohydrates. Exposure to fluorides in optimum concentrations reduces the risk, and normal saliva flow and saliva protective systems are also important to counteract the cariogenic factors.

Untreated caries can give rise to infection of the tooth pulp, which can spread to the supporting tissues and the jaws, culminating in advanced disease conditions that are often painful. For example, in Thailand, recent surveys of a sample of 12-year-old children revealed that 53 percent had suffered from pain or discomfort from teeth over the past year (Petersen and others 2001). The corresponding figures in China were 34 percent for 12-year-olds (Peng, Petersen, Fan, and others 1997) and 74 percent for adults (Petersen, Peng, and Tai 1997).

Tooth decay is a public health problem worldwide. According to the U.S. Surgeon General's report (U.S. Public Health Service 2000), dental caries is the single most common chronic childhood disease in the United States. Epidemiological data for almost 200 countries are available in the World Health Organization (WHO) Country/Area Profile Programme (CAPP) oral health database (http://www.whocollab.od.mah.se/index.html) (see table 38.1 for examples). Caries prevalence of permanent teeth is expressed by the decayed, missing, and filled teeth (DMFT) index (calculated by counting the number of DMFT of individuals and taking the mean for the group examined). One indicator age group used for international comparisons is 12-year-old children. The WHO oral health goal was to achieve three DMFT or fewer among 12-year-olds by 2000. According to the CAPP database, 70 percent of the countries had achieved three DMFT or fewer by 2001, representing 85 percent of the world population. Several developing economies, however, have reported a trend toward higher levels of dental caries.

A detailed analysis of caries data for many countries, both industrial and developing, shows skewed distributions of the diseasethat is, a proportion of a population of children showing a high or very high number of caries and the rest showing a low number of caries or none. Expressing caries prevalence as mean DMFT may, therefore, not accurately describe the disease level in populations with skewed distribution. The Significant Caries (SiC) Index was proposed to bring attention to those hidden high caries groups (Bratthall 2000). The SiC Index is calculated by simply taking the mean DMFT of the one-third of the group having the highest DMFT in a population (figure 38.1). Table 38.1 shows several countries having fewer than three mean DMFT but high SiC Index values, thus illustrating the hidden caries burden for children (Nishi and others 2002).

Dental caries is found not only in children and young adults but also in all age groups. The elderly, in particular those with exposed tooth root surfaces, constitute a special risk population (Barmes 2000). A Swedish study reported DMFT values of 21.4 and 24.4 for 50- and 70-year-olds, respectively, indicating that nearly all teeth were affected in these age groups (Hugoson and others 1995). Thomson (2004), reviewing longitudinal studies of older adults (age 50+), found an incidence of root surface caries varying from 29 to 59 percent and concluded that older people are a caries-active group, experiencing new caries at a rate comparable to that of adolescents. With increasing numbers of people becoming 50 years of age or older in some developing countries, root surface caries may become a significant problem.

When we consider the global epidemiology of dental caries, the main patterns seem to be the following:

• Countries with low mean sugar consumption (less than 10 to 15 kilograms of sugar per person per year) generally have low mean caries prevalence.
• Countries with high mean sugar consumption (more than 20 to 25 kilograms of sugar per person per year) and without effective preventive programs generally have high mean caries prevalence.
• Countries with high mean sugar consumption (more than 20 to 25 kilograms of sugar per person per year) using effective preventive programs have been able to reduce the caries prevalence.

If we consider the prevalence of caries within a population, the main patterns seem to be as follows:

• Disadvantaged or poor population groups have higher dental caries experience than advantaged groups.
• Individuals with poor oral hygiene and frequent sugar intake are at increased risk.
• Individuals not exposed to fluoridesfor example, from fluoridated water or toothpastesare at increased risk of caries.
• Persons with individual risk factors, such as reduced saliva flow or exposed tooth root surfaces, or with certain general diseases are also at increased risk of caries.

Since the discovery of the caries-preventive effect of fluorides in the 1930s, different forms of fluoride administration programs have been implemented, often with remarkable caries-reducing effects. Fluoride has been added to different vehicles, such as water, salt, toothpaste, and milk. Fluoride tablets and fluoride mouth rinsing have been used among young children and in schools, and more recently even among adults at high caries risk (Petersen 1989, 1990). For individual use, fluoride in high concentrations has been added to various forms of gels and varnishes to be applied on the teeth. Furthermore, fluoride in chewing gum is available in some countries. When a group of international experts on cariology were asked in a study to identify the main causes of the caries decline seen in several Western countries during recent decades, practically all the experts pointed to fluoride dentifrice as the most significant factor (Bratthall, Hänsel-Petersson, and Sundberg 1996).

According to WHO (1994), community water fluoridation is safe and cost-effective in preventing dental caries in every age group, benefiting all residents served by the community water regardless of their social or economic status (Burt 2002; Petersen and Lennon 2004; White, Antczak-Bouckoms, and Weinstein 1989). Examples of countries with fluoridated water supplies for significant parts of the populations are Argentina, Brazil, Brunei Darussalam, Canada, Chile, Ireland, New Zealand, the United Kingdom, and the United States. In many developing countries, lack of community water supplies makes water fluoridation impossible.

Effective fluoride toothpastes have been available for about 40 years (WHO 1994). They have been tested in numerous studies, in particular in school-based programs. The most commonly used concentrations are 1,000 or 1,500 parts per million (ppm). Because most studies have been conducted in developed countries, WHO launched a program testing a so-called "affordable fluoridated toothpaste" in developing countries. In the West Kalimantan Province of Indonesia, a supervised school-based toothbrushing program was implemented over a period of three years, resulting in a reduction of 12 to 40 percent of caries incidence in the study groups when compared to control groups (Adyatmaka and others 1998).

Domestic salt fluoridation is another method of automatic fluoridation. In the early 1950s, Switzerland and Austria introduced this approach by offering their populations fluoridated salt for the table and for cooking. The fluoride concentration in the salt originally was 90 ppm and was later increased to 250 ppm. Fluoridated salt is now available in several countries in Europe and in South and Central America. A comparison of caries data for Jamaica in 1984 (before salt fluoridation) and 1995 (after salt fluoridation) showed a reduction of caries experience of 69 percent, 84 percent, and 87 percent among 15-, 12-, and 6-year-olds, respectively (Estupinan-Day and others 2001).

Milk fluoridation projects are being conducted in several countries, including Bulgaria, China, the Russian Federation, Thailand, and the United Kingdom. In Bulgaria, a milk fluoridation project resulted in a 79 percent lower DMFT in those children who had participated in the full five years of the program than in the control children (Pakhomov and others 1995).

Fluoride tablets and fluoride mouth-rinsing programs under supervision in schools have been implemented in several countries, including the Scandinavian countries, the United Kingdom, and the United States. The requirement that teachers and students be motivated has limited such approaches. In recent years, many national fluoride programs have been adjusted as the additional caries-reducing effects of topical applications with daily use of fluoridated toothpaste have been questioned (Petersen and Torres 1999).

The WHO Global Oral Health Programme has developed a manual for integration of oral health with school health programs (WHO 2003). In many industrial countries, school health education programs have included oral health, and researchers have shown that children's self-care capacity improved in regard to regular toothbrushing with the use of fluoridated toothpaste (Flanders 1987; Honkala, Kannas, and Rise 1990; Petersen and Torres 1999; Sogaard and Holst 1988; Wang and others 1998). Examples also exist from school oral health education in developing countries. Some programs have been organized within the context of the WHO Health Promoting Schools Initiative. In Madagascar, the evaluation of program outcomes has shown remarkably good results in reducing dental caries risk, improving self-care capacity of children and mothers, and introducing higher levels of dental knowledge and attitudes (Razanamihaja and Petersen 1999). Other successful examples are available from Tanzania (Petersen and others 2002; van Palenstein Helderman and others 1997), Zimbabwe (Frencken and others 2001), and Namibia (Priwe 1998).

In China, principles from the WHO Health Promoting Schools Initiative have been applied in certain provinces; positive effects of programs were obtained regarding health-related knowledge and behavior, but the clinical outcome measures were less evident (Petersen and others 2004; Tai and others 2001). The Chinese health authorities have emphasized preventive oral care and oral health education since the late 1980s. The nationwide mass campaign "Love Teeth Day" has been conducted annually since 1989, and the effective transmission of oral health messages to the public has shown improved oral health knowledge and behavior in children as well as in adults (Peng, Petersen, Tai, and others 1997).

In addition, various dental organizations (Cohen 1990) and private companies have developed and carried out successful oral health programs worldwide. For example, toothpaste manufacturers have donated toothpastes, toothbrushes, and educational material promoting oral health in several countries.

In countries with systematic national oral disease prevention programs, the total cumulative effect of these programs is reflected in the epidemiological figures demonstrating caries decline (table 38.2) and in the growing proportions of caries-free individuals. However, singling out the effects of specific activities or methods of programs is difficult because several program components often operate simultaneously. For example, in industrial countries, practically all individuals use fluoridated toothpaste, and removing this preventive measure from a group of individuals just to evaluate the effect of another fluoride program would be unethical. In addition, other factors affect caries reduction, such as changing lifestyles, changing patterns of sugar consumption, and improving living conditions.

The current trend in clinical health care and public health is to base recommendations on evidence derived from systematic reviews of the literature and critical assessment of the quality of results (U.S. Public Health Service 2000). The office of the U.S. Surgeon General (U.S. Public Health Service 2000) and the Swedish Council on Technology Assessment in Health Care (SBU 2002) are examples of entities that have attempted to determine the effectiveness in public health of evidence-based approaches and technologies.

Oral Health in America, the U.S. Surgeon General's report (U.S. Public Health Service 2000), reviewed experiences from the administration of fluorides. Primarily based on U.S. studies, the report had these conclusions:

• Strong evidence exists supporting the effectiveness of water fluoridation in preventing crown and root caries in children and adults.
• Strong evidence exists of the effectiveness of the school-based fluoride supplement (tablets) program. The program, with motivated supervising personnel, such as teachers, is recommended for children at high risk for caries.
• Evidence supports the effectiveness of school-based fluoride (0.2 percent sodium fluoride) mouth-rinsing programs conducted before 1985 (before the introduction of fluoride toothpastes) in preventing caries in children. The cost-effectiveness of this intervention is reduced with the current decline in prevalence of caries. It is recommended for use in high-risk children consistently over a period of time.

• Strong evidence supports the effectiveness of sealants in preventing pits and fissure caries. The report recommends that the programs be limited to high-risk children and high-risk teeth.
• Fluoride varnishes were not approved for use in the United States until 1994; hence, investigations are ongoing of the effectiveness of this intervention.

The Swedish Council on Technology Assessment in Health Care (SBU 2002) applied strict criteria of evidence of effectiveness; that is, the study had to be randomized and have a sample representing the total population. For permanent teeth, a three-year follow-up was necessary. The number of studies meeting all the criteria was not very high. Here are some conclusions of this review:

• Daily use of fluoridated toothpaste is an effective method to reduce caries in permanent teeth among children and adolescents. Daily, weekly, or biweekly fluoride mouth rinsing can reduce caries, but together with daily fluoride toothpaste use, the additional effects are not strong.
• Daily fluoride mouth rinsing can reduce root surface caries in the elderly, and professional application of fluoride varnish twice a year has a caries-reducing effect in permanent teeth among youth, as does the use of fluoridated toothpaste.
• Fissure sealants have a caries-reducing effect.

According to the SBU report, it was difficult to interpret the effect of programs aimed at reducing the intake of sugars or the effect of so-called sugar substitutes. Systematic evaluation of community preventive programs should be carried out in the future, particularly to help identify appropriate alternatives for developing countries.