Prediction of Caries Risk and Risk Profiles
Introduction
For successful prevention and control of dental caries in both children and adults, some basic principles must be adopted: For example, the higher the risk of developing caries (new carious surfaces) in most of the population, the greater the effect of one single preventive measure. This may be illustrated by the Swedish experience, where 30 to 35 years ago, caries prevalence was extremely high. Almost every child developed several new lesions every year, mainly because of very poor oral hygiene.
Regular toothbrushing was not an established habit, and no effective fluoride toothpaste was available. Under the prevailing conditions, well-organized, schoolbased fluoride mouthrinse programs in which 0.2% sodium fluoride solution was provided once every 1 or 2 weeks resulted in caries reductions of 30% to 50% (Forsman, 1965; Torell and Ericsson, 1965).
Twenty years later, a 3-year double-blind study revealed no benefit from weekly rinsing with sodium fluoride solutions compared to rinsing with distilled water (Axelsson et al, 1987). There had been a dramatic fall in both caries prevalence and caries incidence from 1964 to 1984, and particularly after 1974, following the introduction of needs-related preventive programs. As an analogy, a raincoat is very cost effective for a week in London in November but not for a visit to the Sahara Desert.
Similarly, at the population level, it is easy to find a positive correlation between one single risk factor and caries incidence in populations with high caries prevalence and incidence, where almost 100% of individuals develop new carious lesions every year.
In such populations, the so-called whole population strategy will be cost effective.
However, in populations with low or moderate caries incidence, well-established selfcare habits, and well-organized oral health care, administration of one single preventive measure to all subjects in the population, irrespective of predicted risk, will not be cost effective; individual risk prediction and needs-related combinations of preventive measures are necessary. To ensure high sensitivity of risk prediction, several etiologic and modifying risk factors must be combined. For cost effectiveness, the so-called high-risk strategy would be the method of choice.
These two conditions may be exemplified by the following: The Vipeholm study (Gustavsson et al, 1954) confirmed 40 years ago that, in the absence of oral hygiene and fluoride, prolonged sugar clearance time was an external modifying risk factor for caries development in mentally handicapped people with heavy plaque accumulation.
The daily intake of sugar-containing products in Sweden has remained unaltered over the last 40 years (about 120 g per individual per day), and the percentage of sticky sugary products consumer, such as sweets and cakes, has actually increased.
However, over the past two decades studies have repeatedly failed to find any correlation between the intake of sugar-containing products and caries prevalence in the population (Sundin et al, 1983; Kristoffersson et al, 1986) Caries prevalence and caries incidence have declined dramatically as a result of integration of caries-preventive measures by self-care, supported by needs-related professional treatment. Particularly successful has been the integration of a self-care program of excellent plaque control and the use of fluoride toothpaste, with professional mechanical toothcleaning and fluoride varnish at needs-related intervals.
In a totally integrated caries-preventive program, however, external modifying risk
factors such as a high frequency of sugar intake should also be addressed.
The risk for caries development varies significantly for different age groups,
individuals, teeth, and tooth surfaces. Therefore, caries-preventive measures must be
integrated and must be based on predicted risk. As an analogy, a medium-sized suit
would not fit all the men in the world; it would be a reasonable fit for at most 40%,
but too small for 30% and too large for the remaining 30%.
In this chapter, prediction of caries risk at the group, individual, tooth, and surface
levels will be discussed in the context of the high-risk strategy. Methods for
prediction of caries risk based on etiologic factors by the combination of salivary
mutans streptococci (MS) levels and Plaque Formation Rate Index (PFRI) as well as
principles for evaluation of sensitivity (percentage of true risk individuals), specificity
(percentage of true nonrisk individuals), and predictive values (positive and negative)
are discussed in chapter 1.
