D E B A T E

Biological and Biopsychosocial Models

© J Can Dent Assoc 1999; 65:496-7

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or more than 200 years, the practice of medicine has specific biological factor. Current scientific knowledge makes
been based on the assumption that a specific etiological it relatively easy to refute this conclusion. For example, the oral
cause (e.g., bacteria, virus) underlies all diseases and cavity in most humans is colonized by Streptococcus mutans,
that treatment should alleviate all symptoms of a disease. But one of the bacteria primarily responsible for caries formation.
recently, the health care establishment has started to re-evalu- However, not all individuals develop caries. The mere presence
ate its position due to changing concepts of health and disease. of a specific biological factor is not always sufficient to cause
Instead of maintaining a narrow focus on the purely biological disease, which suggests that the biological model is inadequate
causes of disease, health professionals in all fields — medicine, in its scope.
dentistry, physical therapy — are now urged to abandon this It is now well established that many diseases display multi-
simplistic view in favour of a more complex model of disease factorial etiologies and that the manifestation of symptoms
that also accounts for psychological and social factors. This requires the complex interplay of several factors. For example,
article explores the traditional (or biological) and contempo- an individual with a high dietary intake of cholesterol may not
rary (or biopsychosocial) models of health and disease and develop coronary heart disease, but if that same individual has
highlights, through specific clinical examples, the superiority a demanding job, does not exercise and has a family history of
of the latter model for modern dental practice. heart problems, there is a greater likelihood that symptoms will
develop. Generally, diseases are therefore caused by the con-
Models of Health and Disease vergence of several factors that can be classified as biological
Most people understand that “health is good” and “disease (e.g., genetics, age), psychological (e.g., attitude, stress) and
is bad,” and while the average person could probably define social (e.g., interpersonal relationships, socio-economic status).
both terms, critical analysis reveals that these concepts defy The scope of this biopsychosocial model is virtually limitless,
simple definition because of the highly subjective nature of an as it can be applied to any individual in any state without
individual’s experience of disease. In 1948, the World Health having to isolate a specific underlying biological cause, which
Organization (WHO) proposed that health is “a complete is sometimes impossible to do.
state of physical, mental, and social well-being and not merely Health and disease are not distinct entities but instead form
the absence of disease”.1 With this definition, the WHO a continuum, with optimum health at one end and death at
sought to replace the biological model of health and disease the other. While optimum health is a goal that can never be
with the biopsychosocial model. truly attained, individuals may alter their lifestyle in order to
A dichotomy between health and disease has been pro- improve their health. At any given point in time, an individ-
moted by the biological model, which has its origins in the ual’s health can be pinpointed somewhere along the continu-
Doctrine of Specific Etiology. In the late 19th century, exper- um; however, this position is in a constant state of flux,
iments by researchers such as Louis Pasteur and Robert Koch depending on the positive or negative effect of daily life expe-
demonstrated that biochemical or physiological lesions could riences, which are influenced by biological, psychological and
cause disease. Their work led to the conclusion that an un- social factors. It is for this reason that the biopsychosocial
affected individual (i.e., without a lesion) would have no model of health and disease is more widely applicable, and
adverse symptoms and be healthy, whereas an affected indi- therefore superior to, the biological model.
vidual (i.e., with a lesion) would necessarily develop symptoms
and be diseased. Health and disease were therefore considered The Concept of Illness
distinct entities, defined by the absence or presence of a An important facet of the biopsychosocial model lacking

496 October 1999, Vol. 65, No. 9 Journal of the Canadian Dental Association
 Biological and Biopsychosocial Models of Health and Disease in Dentistry

from the biological model is the concept of illness, which eliminating that cause. In the second case, the dentist may
refers to a person’s individual experience of disease.2 Illness is uncover more general psychological and social factors con-
a subjective measure of disease, in contrast to strictly objective tributing to, or stemming from, the periodontitis. The dentist
indices such as body temperature or cholesterol level. The can then tailor a treatment plan specifically geared to the
development of an illness is not limited to a biological dis- patient’s individual needs, thereby increasing the likelihood of
equilibrium; psychological and social factors can influence a compliance. A treatment plan is only effective if the patient fol-
patient’s reaction to his or her condition. The concept of ill- lows it; simply telling someone to floss more, without knowing
ness, therefore, reflects more accurately the complexities of the why that person doesn’t, is not likely to lead to positive change.
biopsychosocial model of health and disease.
The concept of illness blurs the rigid distinction between Conclusion
health (good) and disease (bad) established by the biological The biological model of health and disease is outdated and
model. For example, consider two individuals, each with a inadequate. Health and disease can no longer be considered
deep carious lesion. Patient A is relatively unaffected by the distinct entities where one exists only in the absence of the
cavity: he tolerates the pain well, such that his psychological other. A physiological condition that prompts one person to
state is unaltered, and continues to socialize. Patient B is both- seek medical or dental treatment may be perfectly acceptable
ered by the cavity: he is preoccupied with the pain, such that to another person. Therefore, despite the importance of
his general attitude has deteriorated, and does not socialize. biological phenomena with respect to the etiology of diseases,
While both individuals have the same underlying biological thorough evaluation of a disease cannot be based solely on bio-
problem, they experience it differently as a result of psycho- logical factors. Indeed, psychological and social factors must
logical and social factors. Patient A considers himself healthy, also be considered, such that the question of what is healthy
while patient B considers himself unhealthy (or diseased). and what is not becomes very subjective, and is more properly
Their individual subjective experiences determine the extent explained by the concept of illness. Whereas the biological
of their illness and the impact it has on their quality of life. model restricts itself to searching for a specific underlying
cause of disease, the biopsychosocial model explores all aspects
Comparing the Models of an illness, and is thus a more valuable diagnostic tool for the
The practical benefits of applying the biopsychosocial
modern dental practitioner.
model of health and disease to modern dental treatment can
best be illustrated with a clinical example. Consider a patient
with adult chronic periodontitis who does not floss. A dentist Acknowledgments: The author would like to thank Dr. Paul
following the biological model may suggest that the patient Allison, assistant professor in the faculty of dentistry at McGill
University, for his valuable insights.
floss every day to remove the bacteria implicated in the etiol-
Mr. Deep is a third-year student enrolled in the DMD program
ogy of periodontitis. A dentist following the biopsychosocial
at the faculty of dentistry, McGill University.
model may make the same suggestion, but will also delve fur-
The views expressed are those of the author and do not necessari-
ther into the patient’s history, asking why the patient doesn’t ly reflect the opinion and official policies of the Canadian Dental
floss (“I have arthritis in my hands”), why the patient chose to Association.
seek treatment now (“It hurts”), how the periodontitis makes
the patient feel (“I can’t take it anymore”), what the patient
eats, and what sort of home oral care, if any, the patient References
practises. 1. WHO. International classification of impairments, disabilities and handicaps.
In the first case, the dentist assumes a specific underlying Geneva: World Health Organization; 1980.
biological cause and recommends a treatment aimed at 2. Mechanic D. Medical sociology. New York: Free Press; 1968.

Journal of the Canadian Dental Association October 1999, Vol. 65, No. 9 497