"The oral cavity is an in integral part of the body"

Dental Tribune Online: How has our knowledge about the oral microbiome and its link with general health advanced in recent years?
Prof. Lakshman Samaranayake: The microbiome, for those unfamiliar with the term, is defined as the totality of organisms and the environment within which they reside. Recently, there has been a profound and a remarkable advance in the knowledge and understanding of the microbiome owing to the advent of sophisticated analytical techniques such as next-generation sequencing. “Microbiota” is the specific term used to describe the organisms living within the microbiome, and a predominant proportion of oral microbiota reside within plaque biofilm communities attached to oral surfaces such as teeth and gingivae.

In the oral cavity, we have three major sub-compartments of the microbiome, namely the bacteriome (bacteria), the mycobiome (fungi) and the virome (virus). In health, these organisms live together in harmony in polymicrobial communities exhibiting many symbiotic relationships. However, such symbiotic relationships can be perturbed for various reasons, such as antibiotic intake and poor oral hygiene. This, then, leads to a dysbiotic relationship when disease sets in. Classic examples are poor oral hygiene leading to gingivitis and periodontitis, and Candida (yeast) overgrowth due to broad-spectrum antibiotic use.

The probable association between oral and systemic health has been known from the time of ancient Greek physicians such Hippocrates and Galen. They considered that poor oral health could have an impact on overall systemic health. This notion once again became popular after the work of researchers such as Syrjälä and Matilla, who published seminal studies on the strong association between heart disease and poor oral health in large cohorts of Finnish populations in late 1980s. Currently, there are virtually hundreds of studies implying a possible association between poor oral health and atherosclerotic vascular disease, for example.

What other connections to general health conditions have been found so far, and how profound is the evidence for them?
As mentioned, of all the diseases studied to date, there is a very strong database linking atherosclerotic vascular disease (ASVD) and poor oral health, particularly periodontal disease, which is mainly a biofilm-related infection, though there are other contributory factors, such as host immunity. The scientific community has been hard at work attempting to decipher the possible link between oral health and various other diseases.

Most of the studies are indeed on ASVD, but adverse pregnancy outcomes and low birth weight babies, diabetes and hospital-acquired pneumonias have all been studied intensively. However, data on the last three conditions is not as solid as for ASVD. One reason for the plethora of studies on ASVD appears to be the wide availability of numerous funding provisions that sponsor cardiovascular disease research, including hyperlipidaemias, stroke and related illnesses.

Other diseases that are currently being investigated for a link on the oral–systemic axis include dementia and Alzheimer’s disease, oral carcinomas, pancreatic cancer, rheumatoid arthritis, obesity and renal disease, to name but a few. Indeed, there is recent work indicating that erectile dysfunction may be linked to poor oral health. If that were the case, then dental professionals could use this evidence as a real practice builder.

How does this knowledge change the way medical and dental professionals should be approaching disease?
The oral cavity is an in integral part of the body. Gone are the days when dental professionals treated only the tooth, not truly comprehending that a person is attached to the tooth. Personalised medicine is now at our doorstep and personalised dentistry should not be too far away. Hence, we, as a profession, have an obligation to learn and educate ourselves about the myriad possible links between oral health and systemic health/disease.

For instance, salivary diagnostic procedures for systemic disease have come of age and are relatively common, at least in the developed world. Diagnosis of HIV disease, viral hepatitis, and diabetes, for instance, could therefore be in the realm of future dental practice. Work of researchers at the University of California, Los Angeles, has shown that isolation of specific target organisms in tandem from saliva could be a harbinger of pancreatic cancer. Hence, it is highly likely that the future professionals will have a more demanding role not only as accomplished dentists in various new technologies, but also as practitioners that work in tandem with a team of physicians and paramedical professionals in managing diseases such as diabetes and cancer.

Yet, to make this a reality, we need to address one more issue. That is the liaison between medical and dental professionals. In the US, for instance, physicians are fully aware of the probable link between oral and cardiac health, and even the American Heart Association website specifically states that oral health is a key factor in cardiac health. Unfortunately, though, in this part of the world and Asia, we seem to be lacking such interprofessional rapport and understanding. Thus, we have a great challenge here to educate our medical brethren and, in professional terms, a broader societal task to accomplish.

Last but not least, patient education should not be forgotten. It is imperative that we educate our patients on the possible links between oral and systemic health. For instance, pregnant mothers should be educated on the probable association between oral health and adverse pregnancy outcomes, including premature birth. The latter eventuality will have a great emotional and financial toll on not only the parents, but also the baby, who may have lifetime disabilities due to the prematurity, hence the critical importance of good oral hygiene in maintaining the health of not only the mother but likely the unborn baby. A single scaling and debridement will benefit both the mother as well as the unborn baby.

What factors can change the balance of the natural oral microbiome, and are there certain groups at higher risk?
As we are all aware, routine oral hygiene, such as daily, regular toothbrushing and flossing regimens, as well as periodic scaling and debridement, are critical for the maintenance of a healthy oral microbiome. The oral microbiome and the resident microbiota help maintain our oral health by inhibiting the invasion of extraneous organisms such as coliform bacteria, but above all, by preventing the overgrowth of periodontopathic organisms such as Porphyromonas gingivalis, Tannerella forsythensis and Treponema denticola.

The healthy oral microbiome is analogous to a community of humans of various shapes and sizes living in harmony and peace. As we all know, however, this harmony can be shattered and disrupted by criminal elements of the community. Similarly, the aforementioned periodontopathic bacteria, for which I have coined the term “terrorist bacteria”, can wreak havoc and proliferate within plaque biofilms, destroying the ecosystem and the community, leading to gingivitis and periodontitis. Hence, the main purpose of a healthy microbiome is to keep these unwanted criminal bacterial elements at bay. Thus, good oral hygiene is paramount and is the most critical factor that overarches a good eco-balance of the oral microbiome.

Besides this, there are other local and systemic factors that may impact on the harmonious livelihood of the oral microbiome. These include having a good salivary flow and a healthy dentition devoid of carious teeth. Saliva has intrinsic immune mechanisms that appear to foster a healthy oral microbiome while keeping invading organisms at bay. For instance, salivary leucocyte protease inhibitor is known to block the cell surface receptors of the oral epithelium essential for the entry of HIV, the agent of Aids. As mentioned, for reasons that are inexplicable, uncontrolled diabetes mellitus leads to gingivitis and periodontitis, and hence it is critical that diabetics meticulously maintain their oral hygiene.

What are the best strategies to maintain and re-establish the natural balance of our oral microbiome, and does clinical practice has to be transformed?'
Given our current knowledge of the oral ecosystem in health and disease, dental professionals have to emphasise the crucial importance of conservation of a good oral microbiome and a heathy community of oral bacteria to preserve oral health. Their main strategy should be to eliminate the “criminal elements” of the oral microbiome that are currently thought to be responsible for caries, gingivitis and periodontitis.

There is currently a debate, especially in the US, on whether to floss or not to floss regularly. Flossing should be an adjunct to eliminate plaque microbiota from inaccessible niches of the oral cavity due to situations such as imbricated teeth, or due to recession of gingivae, and shallow periodontal pockets. Flossing is also useful to eliminate plaque biofilm when appliances are worn.

Finally, the chemomechanical removal of plaque biofilm by regular rinsing has been a vexed question in the dental community. My belief is that regular oral rinses with various antiseptics have a useful place under certain circumstances, such as in managing individuals unable to conduct good plaque biofilm control through regular and regimented toothbrushing, such as debilitated hospitalised patients, those living in special care institutions owing to mental disabilities or those who are physically handicapped.

As far as I am concerned, a chemomechanical strategy of biofilm removal should be directed towards converting a dysbiotic microbiome into a symbiotic microbiome, that is eliminating “terrorist bacteria” and restoring a healthy oral microbiome. Unfortunately, we do not have, as yet, a chemical antiseptic that targets only the “nasty/terrorist” bacterial elements, and antiseptic use will generally lead to blanket suppression of the good as well as the bad bacteria. Hence, it appears that the purpose of a chemomechanical approach to oral health is to restore the healthy eco-balance of the oral microbiome from a dysbiotic to a symbiotic state compatible with health.

What lessons will participants take home from your lecture at AEEDC Dubai?
As far as the oral–systemic axis is considered, there are many studies indicating the probable association between poor oral health and ASVD, diabetes mellitus, adverse pregnancy outcomes and low birth weight babies, as well as hospital-acquired pneumonias. Yet, it must be remembered that these are all still considered mere associations. An association does not necessarily prove causality. Of those discussed, the association between poor oral health and ASVD seems to be the strongest.

There is a dire societal need for us as dental professionals to educate not only our patients but also the general public, as well as the medical community, of the paramount importance of oral health in maintaining good systemic health. A good oral microbiome is essential to maintain homeostasis of a healthy oral cavity. Indeed, we cannot live without a good microbiome, as many studies have shown that animals without a microbiome do not survive, and they shrivel and die. Good bacteria are our friends and we cannot live without them.

Oral biofilms, in the form of plaque, are the predominant constituent of the oral microbiome, although the suspended bacteria in the planktonic form make up a significant proportion of the microbiome.

Last but not least, some biofilm constituent bacteria (i.e. the bad or the “terrorist” bacteria) can destroy the oral microbiome community and cause disease by subverting a symbiotic relationship to a dysbiotic one.

Thank you very much for the interview.

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