Correspondence Address:
Prof. Solomon Olusegun Nwhator
Department of Preventive and Community Dentistry, Faculty of Dentistry, Obafemi Awolowo University, Ile-Ife, Osun State; Obafemi Awolowo University Teaching Hospital, Ile-Ife, Osun State; Editor-i-Chief, Nigerian Dental Journal

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The notion that the mouth is the mirror of the body no longer holds. More than a mirror, the mouth exerts pan-systemic effects on systemic health and disease.

Hippocrates of ancient Greece and Galen of ancient Rome were credited to the first mentions of the oral-systemic associations in 400 BC and 166 BC, respectively. JD Miller's 1891 classic − 'The Human Mouth as a Focus of Infection chronicled over 100 cases of non-oral diseases ascribable to dental/oral origins and William Hunter's work titled 'Oral Sepsis as a Cause of Disease' implicating poor oral health in the aetiology of several systemic diseases was published by the BMJ 1900. A decade later, Billing's 'focal infection' theory, Berger's focal allergy theory and Slauk's focal toxicosis theory of the peri-1940s were propounded. Unfortunately, these ideas resulted on wide-scale extractions and tonsillectomies until Cecil and Angevine published their work in 1938 to put a check on the practice.[3] By the 1940s, scientists had trashed the notion of oral-systemic health links along with prescriptions such as the urine of a faithful wife as a cure for conjunctivitis!.[5]

A 1982 report of a 'sperm immobilising factor' isolated from necrotic dental pulp and Bieniek and Riedel's 1986 report of antibiotic-resistant bacteriospermia in potential sperm donors which resolved spontaneously after sessions of oral/dental treatments fanned the moulders of the plausibility of oral-systemic health links.[2],[4] The striking similarity between donors' intraoral bacterial spectrum spermiograms rekindled questions of oral-systemic health associations. With an improved understanding of periodontal inflammation, scientists later showed that proteolytic enzymes from periodontal inflammation destroy surrounding gum tissues and induce persistent systemic inflammation. The 'second wave' of the mid-1980s to the early 1990s added impetus to the thought that oral health might be total health. However, the scientific community, now more cautious, needed more evidence.

The latest wave of potential oral-systemic health links is now easier to explain. The important oral-systemic interface is termed the junctional epithelium – a semi-permeable lining around teeth, between the hostile oral microbe-laden environment and the systemic circulation. A clear pointer to this is bleeding gums while brushing teeth. Gums bleed because of inflammation-induced damage to the gingival microvasculature. With moderate to advanced gum disease, the junctional epithelium suffers extensive ulceration with a surface area equivalent to that of an adult palm! This 'open wound' sustained by inflammatory mediators serves as a direct link between the oral environment and the systemic circulation, with attendant consequences. The consequences arise from the 'cytokine storm' akin to that alluded to in recent scientific literature. The systemic circulation transports these cytokines far and wide, exerting influences far away from the mouth, hence the 'endocrine hypothesis.'

A review of systems forecloses the possibility that the observations of the early Greeks and Romans were wrong. The observations were probably correct, but science at the time lacked the tools to fully investigate the phenomena. While cytokines and other inflammatory mediators make it through the semi-permeable junctional epithelium, microbes also find their way through. Probably the strongest explanation for this is the discovery of Porphyromonas gingivalis – a well-known periodontal pathogen as a potent risk factor for Alzheimer's disease discovered in the brain of Alzheimer's disease patients.[7] Before this, gum disease-associated pathogens have been detected in the brain through genetic ribotyping. These observations naturally gave birth to the other phenomenon referred to as 'haematogenic metastatic theory' in the aetiology of gum disease-associated systemic diseases. Thus, the central nervous system suffers heavily from gum disease-associated diseases previously missed by scientists and researchers.

Oral health also affects the endocrine system. Gum disease-associated cytokines – interleukin-1 and tumour necrosis factor-α are potent insulin antagonists, thus explaining the causal link between gum disease and poor glycaemic control validated by meta-analysis.[1] The circulatory system is not left out with the result of cultures of arterial plaques yielding positive growths of P. gingivalis - a notorious periodontopathic organism. The isolation of platelet aggregation-associated protein produced by this organism from such plaques adds strength to the observation, while the associated thrombus formation easily explains the association between gum disease and stroke. With the reproductive system comes the link between gum disease and oligospermia, reduced sperm motility, erectile dysfunction, increased time to conception, preterm labour and low birth weight, all being part of the growing list of oral-systemic associations.[6]

With the mouth being part of the digestive system, a link between gum disease and peptic ulcer disease is not surprising with a hypothesised direct dislocation of Helicobacter pylori from infected periodontal pockets, which also explains the link between gum disease and aspiration pneumonia. From the microbiological standpoint, some periodontal pathogens are worthy of special mention, namely Escherichia coli and Fusobacterium nucleatum, implicated in the association between gum diseases and serious systemic diseases such as reduced sperm count and duodenal cancer attributed to the gate opening effect of F. nucleatum. The presence of F. nucleatum is associated with poor prognosis oesophageal, pancreatic, colon and rectal cancers as well as treatment failure in oesophageal and colorectal and cancers.[8]

From the foregoing, there is an urgent need for a paradigm shift from the notion of the mouth being the gateway to the body, which informed oral checks for pallor, jaundice, dehydration and the like. The mouth exerts system-wide influences with pan-systemic effects. We must also abandon the one-jacket-fits-all advice of twice-yearly visits to the dentist. The current emphasis is individualised, biomarker/big data-driven next generation, predictive diagnosis. This empowers general and oral health physicians to institute interceptive oral/systemic care ahead of overt clinical changes. That oral health is total health is, therefore, no longer debatable, but most of our teeming population is oblivious to these links and associations. Doctors, dentists, nurses and all health workers will do well to sound the trumpet loud and clear that oral health exerts a pan-systemic influence on the body. Aside its effects on the nervous, reproductive, circulatory, digestive and other systems, poor oral health also affects social interactions and leads to depression. Since total health is a state of complete physical, mental and social well-being. Oral health is indeed total health!

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