This chapter introduces important epidemiologic concepts and reviews what is known about the epidemiology of specific orofacial pain conditions. The aim is to provide an understanding of how epidemiologic data can contribute to clinical practice as well as to provide information on the rates of and risk factors for specific orofacial pain problems.
What Is Epidemiology?
Epidemiology is the study of the distribution, determinants, and natural history of disease in populations.1 Although epidemiology has traditionally focused on well-defined diseases, epidemiologic methods are increasingly employed to study symptoms such as pain and other conditions for which patients are defined based on self-report or a combination of self-report and clinical findings. Morris2 has identified seven uses of epidemiology. For the clinician, the most important of these are the following: The use of epidemiologic data (1) in predicting an individual’s risk of having or developing a particular disease or disorder; (2) in completing the clinical picture, that is, in understanding where in the spectrum of disease an individual patient’s condition falls; and (3) in the clues it may provide about causes of a disease and, therefore, possible approaches to its treatment. Knowing the rates with which specific pain conditions occur in the population as a whole, as well as their rates in specific age and sex groups, can aid the clinician in thinking about the most probable diagnosis in a particular patient. Of course, a thorough history, examination, and appropriate diagnostic tests are warranted in any patient before making a definitive diagnosis.
Inherent in the definition of epidemiology are three important perspectives3: (1) the population perspective, which implies that, to understand the full spectrum of pain problems, pain conditions must be studied in entire populations, not only in persons seeking treatment; (2) the developmental perspective, which suggests that understanding pain across the life cycle is essential because factors influencing a specific pain condition may vary with age; and (3) the ecologic perspective, in which disease agents, characteristics of the host, and characteristics of the environment are all important in determining whether or how a condition manifests itself in a given person. This is similar to the biopsychosocial perspective on pain, which views pain as the result of the dynamic interaction of biologic, psychologic, and social factors.
Most of the epidemiologic data on chronic orofacial pain are prevalence data. Prevalence is simply the proportion of the population with a condition at a given time. Prevalence differs from incidence, which is the rate of onset of new cases of a condition over a specific period, usually a year. Incidence and prevalence are related such that:
Prevalence = Incidence × Mean Duration
It makes sense that the number of cases in the population at any given time is a function not only of the rate at which new cases occur but also of how long the condition typically lasts. (If the rate of onset of two conditions is the same, but one lasts 1 year and the other lasts 2 years, twice as many cases of the second condition will be found at any given time.) Although pain arising from caries and periodontal disease is generally acute if treatment is provided, most other orofacial pain conditions in the population follow a chronic-recurrent course.
In the epidemiologic sense, risk is the likelihood that people without a disease who are exposed to certain factors (called risk factors) will acquire the disease. It is useful to think about two kinds of risk factors: those that we can change, like smoking, are known as modifiable risk factors; and those that we cannot control, like age and sex, are sometimes called risk indicators.
Orofacial Pain Conditions
Toothache, periodontal pain, and oral soft tissue pain
Because caries is the most common cause of pain in the teeth, the prevalence of toothache in a population depends on the rate of caries and the factors that influence that rate, such as diet, social class, and levels of fluoride in the water supply. One US national study4 found an overall prevalence of 12.2% among adults for toothache in the preceding 6 months, with little difference in prevalence rates for men and women. Rates decreased with age from 16.9% in 18- to 34-year-olds to 3.4% among those aged 75 years or older. A slightly higher prevalence was found in a survey of Toronto residents,5 where 14.1% of adults reported experiencing toothache in the previous 4 weeks. Toothache is likely the most common cause of orofacial pain among children; for example, a study of Australian schoolchildren found that about 12% had experienced at least one toothache before their fifth birthday, and almost one-third (31.8%) had experienced toothache by the age of 12 years.6
Few epidemiologic investigations of pain in the periodontal and oral soft tissues have been conducted. Population-based studies of herpes simplex and aphthous stomatitis, common oral lesions that typically cause acute, self-limiting pain, have found point prevalences of 1.6% and 0.9%, respectively.7 Pericoronitis, an acute infection around erupting third molars, commonly causes acute pain and trismus among persons in their late teens or early twenties, although no population-based prevalence data have been reported.
Temporomandibular disorder pain
Temporomandibular disorders (TMDs) are musculoskeletal conditions characterized by pain in the temporomandibular joint (TMJ) and/or the associated muscles of mastication (see chapters 17,18, and 22). TMD pain is by far the most common chronic orofacial pain condition, and it is similar to back pain in its intensity, persistence, and psychologic impact.8 TMD pain is rare in children prior to puberty.9 Table 2-1 lists several studies that inquired into the presence of ongoing pain in the temporomandibular region in adult populations (for review, see Drangsholt and LeResche.9). Rates range from 9% to 15% for women and from 3% to 10% for men. Considering the differences in definitions and in populations examined in the different studies, these rates are remarkably consistent. Interestingly, TMD pain appears to be 1.5 to 2 times as common in women than in men in nearly every study. Also, in all studies where there was a clear pattern for age-specific prevalence, the peak age was around 35 to 45 years.