An introduction to periodontal medicine

Do the periodontal and systemic diseases have any link? Researchers have been trying to find out the answer to this question for a long time. As we know that periodontitis is the inflammation of periodontal tissues, the periodontal infection may act as a focus of infection for systemic diseases. This area of research in periodontology, which relates periodontal diseases to systemic diseases is known as “Periodontal medicine”. The term ‘Periodontal medicine’ was first suggested by Offenbacher (1996) 1. This field of periodontology encompasses the study of the contribution of periodontal infections on several systemic conditions such as atherosclerosis, myocardial infarction, stroke, diabetes, and premature delivery. World Workshop in Periodontics 1996 introduced the term “Periodontal medicine” to describe the study of the connection between other systemic pathologies and periodontitis. Let’s try to understand the basic concepts in periodontal medicine.

Focus of infection

A focus of infection is a confined area which contains pathogenic microorganisms, that can occur anywhere in the body and usually causes no clinical manifestations. A focal infection is a localized or generalized infection caused by the dissemination of microorganisms or toxic products from the focus of infection 2.

Historical aspect of focal infection theory

The hypothesis that oral infection can act as a source of systemic infections (focal infection theory) is more than a century old. In 1890, WD Miller published a paper titled “The micro-organisms of the human mouth: The local and general diseases which are caused by them” wherein, he considered oral infections as the prime cause of systemic diseases 3, 4. According to him, oral microorganisms and/or their products had an important role in the development of a variety of diseases, including brain abscesses, pulmonary diseases, and gastric problems, as well as a number of systemic infectious diseases 5.

This theory was widely accepted between 1900 to 1940 6 which resulted in radical dental treatments (like,  extraction for caries, gingivitis, and periodontitis), which were advised as a solution for systemic 7, 8 diseases. After 1940, the focal infection theory faced resistance, largely due to the lack of scientific evidence, the discovery of antibiotics and unacceptable treatment options 9.

This theory fell into controversy when in 1952, an editorial in the Journal of the American Medical Association stated that “many patients with diseases caused by foci of infection have not been relieved of their symptoms by removal of the foci. Many patients with these same diseases have no evident focus of infection; also, foci of infection are as common in apparently healthy persons as those with disease” 5. The focal infection theory was not revisited for the next 50 years.

Then, in 1986 Löe et al. 10 and others published a landmark paper which was the beginning of host immune response and bacterial interaction paradigm of periodontal disease progression. He examined a group of male tea workers in Sri Lanka over a period of 15 years. These men did not use any oral hygiene methods and had no access to dental care, allowing the study of the natural progression of the untreated periodontal disease. The results of the study showed that all individuals were not equally affected. The vast majority (81%) of the men showed moderate progression in attachment loss, 11% did not progress beyond gingivitis and the remaining group (8%) exhibited rapid loss of attachment, losing between 10 and 32 teeth over 15 years. The findings of the study had following conclusions:

  1. Gingivitis is present at an early stage in the progression of periodontal diseases, but it may or may not progress to periodontitis.
  2. Most importantly, it proposed that periodontal disease progression is multi-factorial i.e. factors other than the microbial etiologies are involved in the progression of periodontal diseases. These factors are known as the risk factors. Risk factors are defined as “an aspect of personal behavior or lifestyle, an environmental exposure, or an inborn or inherited characteristic, which on the basis of epidemiologic evidence is known to be associated with a health-related condition” 11. Examples of some risk factors for periodontal diseases are; genetic factors, systemic disease like diabetes, and environmental factors like smoking, stress etc.

Focal infection theory revisited

In 1910, a British physician, William Hunter, presented a lecture on the role of sepsis and antisepsis in medicine to the faculty of McGill University, where he condemned the practice of dentistry in the United States, which emphasized restorations instead of tooth extraction. The pulpless teeth (teeth with necrotic pulps) and endodontically treated teeth were also implicated as the focus of infection. This was followed by long-term studies, which disapproved this concept 12. In the 1930s, editorials and research refuted the theory of focal infection and called for a return to constructive rather than destructive dental treatment rationale 13, 14. A classical article by RA Hughes (1994) 8 discussed all the facts relating to the focal infection theory and also presented the focal infection theory revisited. The three mechanisms by which oral micro-organisms can contribute to systemic diseases are 15,

  1. Metastatic infection caused by translocation of bacteria.
  2. Metastatic injury related to microbial products which enter the blood circulation.
  3. Metastatic inflammation due to immune injury.

The junctional epithelium and the sulcular epithelium are the primary sites for host-bacterial interactions. The junctional epithelial cells initiate the host inflammatory response against the microbial challenge 16. However, due to increased microbial load and virulence, the epithelial barrier is breached, creating ulcerated areas from where microorganisms and their products get an access to the underlying connective tissue and blood capillaries. During brushing and eating, these ulcerated areas provide a gateway for the …………


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Certain bacterial antigenic proteins (such as bacterial heat shock proteins) may have homogenicity with host proteins (host heat shock proteins), which may result in cross-reactivity of antibodies. This results in autoimmune injury to the host. Table… describes various non-oral diseases which may have an origin in the oral cavity.

The pathways of systemic association of oral infection and probable diseases caused 19, 20 

Pathways of spread of oral infections
Probable diseases caused
Metastatic infections caused by transient bacteriemia caused due to dental procedures Subacute infective endocarditis, acute bacterial myocarditis, brain abscess, cavernous sinus thrombosis, sinusitis, lung abscess/infection, Ludwig's angina, orbital cellulitis, skin ulcer, osteomyelitis, prosthetic joint infection
Metastatic injury resulting from the circulation of oral microbial toxinsCerebral infarction, acute myocardial infarction, abnormal pregnancy outcome, persistent pyrexia, idiopathic trigeminal neuralgia, toxic shock syndrome, systemic granulocytic cell defects, chronic meningitis
Metastatic inflammation caused by immunological injury from oral organismsBehçet's syndrome, chronic urticaria, uveitis, inflammatory bowel disease, Crohn's disease

Evidence-based clinical practice

Evidence-based practice has been defined as the practice of dentistry that integrates the best available evidence with clinical experience and what a patient prefers in making clinical decisions. A good quality research work has provided us with the evidence of the relationship of periodontitis with cardiovascular conditions 21-23, diabetes mellitus 24-27, preterm low birth weight 28-30, respiratory conditions 31, 32 etc. A lot of research work has been done in the field of periodontal medicine. Presently, we have a large number of quality epidemiological and microbiological-immunological studies that have lent credence to the concept that periodontal disease may be a separate risk factor for cardiovascular disease, cerebrovascular disease, and respiratory disease, as well as preterm delivery of low birth weight infants 33, 34.


In this chapter, we discussed the basic mechanisms which relate periodontal diseases to systemic diseases. A lot of research has been done, relating periodontal diseases to various systemic diseases. However, it should be remembered that the proposed pathways relating periodontal to systemic diseases are based on the three basic mechanisms which have been explained earlier in this chapter. In the next chapters, we shall discuss individual systemic diseases and their link to periodontal diseases in detail.

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