When diseases become more common, we need to be educated about their effects on the provision of dental care and be able to evaluate and assess their status and severity.
During the past four to five decades, a dramatic increase in the incidence of a number of chronic conditions has been noted among children in the United States and in other industrialized nations. These conditions include asthma, attention deficit disorder/attention deficit hyperactivity disorder (ADD/ADHD), diabetes mellitus and obesity, and they are having a disturbing effect on our health care delivery systems.
Changes in diet and physical activity/inactivity levels may explain some of the observed increase in diabetes and obesity. Efforts to link specific behaviors to biological processes may have spurred the rise in the diagnosis of ADD/ADHD. The proliferation of asthma in children is harder to explain, though theories abound.
One theory that has been around for almost 30 years is the "hygiene hypothesis."1 Basically, this theory posits that fewer exposures to microbial agents through unhygienic prenatal or early childhood interpersonal contacts could predispose a person to the development of atopic disorders.
With today’s smaller families and more sanitary conditions at home, children’s immune systems are dominated by a specific T-helper lymphocyte: type 2 helper (Th2) T-cells. The result is a predisposition to allergic rhinitis and asthma, which is seen increasingly in more affluent, Western, industrialized nations. Have we become, in effect, too clean?2
Epidemiologic data actually may support the observation of increased atopic disorders in small, well-off households. Asthma and related illnesses may be affected, and it also has been proposed that diseases such as multiple sclerosis may be associated with a lack of childhood exposure to specific pathogens.3 This development may be due to an immune response dominated by another T-helper lymphocyte: type 1 helper (Th1) T-cells, which may predispose a person to autoimmune disorders, including type 1 diabetes mellitus.
There appears to be an even more intriguing biological basis for the hygiene hypothesis. Apparently, apart from developing infectious diseases in early childhood, exposure to environmental bacterial products such as endotoxins may be enough to spawn an inverse relationship between bacterial burden and atopic disorders. This was shown in a study exploring the composition of dust collected from homes of children in a single community who were or were not exposed directly to farm animals.4,5 The dust from homes in close contact with animal farms contained markedly higher levels of endotoxins. Early and frequent exposure to these endotoxins could be reasons for the reduced susceptibility to allergic reactions. The association between endotoxins in household dust and the subsequent risk of developing asthma was shown to exist in urban settings as well.6
The microbial burden in the oral cavity is well-known. If the hygiene hypothesis is valid, we may have another piece of the puzzle to the association between oral and general health. An interesting study addressing this relationship evaluated the connection between Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis.7 Higher concentrations of immunoglobulin G antibodies to P. gingivalis were associated with a lower prevalence of asthma. This was a cross-sectional study and cannot invoke causality. However, it raises an intriguing question about prenatal exposure to maternal periodontal microbial burden and a propensity to develop asthma, allergies and other immune-mediated conditions later in life.
Changes in the incidence of diseases have an effect on education, as well as the practice of many health care fields. When diseases become more common, we need to be educated about their effects on the provision of dental care and be able to evaluate and assess their status and severity. When new information makes some conditions less important, we can afford to pay less attention to them. The most recent guidelines from the American Heart Association on infective endocarditis make this point.8 Our earlier preoccupation with heart murmurs no longer carries the same importance it once did.
As addressed in a previous editorial, epidemiologic changes and discoveries also affect the development of health questionnaires.9 Epidemiologic changes challenge and stimulate our inquisitiveness, and if we act on them, we can become important participants in the quest to elucidate the etiologic and pathologic pathways of diseases that affect our patients. But more importantly, understanding the reason for these epidemiologic trends may help us provide better overall care for our patients.
