The Science of Oral-Systemic Connections

“The oral-systemic connections are accepted at this point by both the medical and dental professions. The strength of the links is still under investigation. It is important to understand that there is not a single connection, but rather links for a variety of organ systems and disease entities…

Some connections are well-established, such as respiratory infections derived from inhaled oral pathogens. The association between periodontal disease and diabetes is also well-established, with a large body of evidence demonstrating the two-way relationship between them.”

– Richard H. Nagelberg, DDS, Dental Economics (1)

Oral-Systemic Links is a growing body of scientific studies on mouth-body connections. There is not one, but many connections, says Dr. Nagelberg, who specializes in periodontal disease and its effect on the body. Another connection is the Oral-Airway connection, which is the focus of this book.

Let’s start with two studies linking mouth health to pneumonia in hospital intensive care units as examples:

  • A simple oral rinse (Peridex, 0.12% chlorhexidine gluconate) can cut hospital-acquired pneumonia in open-heart surgery patients on ventilators by 52%. (1)
  • A later study confirms that (a) tooth brushing has no effect, and (b) Peridex significantly reduced pneumonia in intensive care units. (2)

Just keeping patients’ mouth clean can cut hospital-acquired pneumonia by half, and save lots of money and trouble with a simple oral rinse. We can appreciate its usefulness, can’t we?

These studies indirect confirms the mouth’s strategic location in the reparatory tract, which is how dentists can have a major role in snoring and sleep apnea. More on that later.

Bit by bit, science is confirming common sense that a healthy mouth is foundational to whole body health. Since this book is primarily for patients and parents, available studies will be cited without being exhaustive. Still, the map is far from complete. So here are a few pointers on how to navigate the emerging field of Mouth-Airway connections ahead.

Science vs. Common Sense

Oral-Systemics is a new frontier, but only in health science. Common sense tells us that the mouth that feeds the heart and the brain, which in turn support the mouth. A German proverb says, “In the intestines lies Life, or Death.” The Chinese say “Disease enters by mouth, and disaster exits by mouth.” But credible doctors must speak from evidence in the form of published studies. So you will see many of them ahead.

But what’s the patient to do when the search engine puts all the studies and knowledge on your computer screen? How can you tell which ones to trust, or which ones do not apply to your own case? That’s where a doctor’s training and clinical judgment comes in.

As the patient, you can use your common sense, ask WHY like a grade school kid. Can a cleaner mouth reduce infection? How else can the mouth be made cleaner? Why do those patients need to have open-heart surgery in the first place? Does the mouth have anything to do with having to go to the hospital in the first place? Common sense can give you most of the answers.

The point here is to use your symptoms as the start, your goals as the end, and work with your doctor(s) to find studies that can validate your health habits and treatment plan.

Evidence-Based Science: Limitations and Questions

Studies are useful, but researchers will be the first to say studies have limitations. Scientific studies isolate parts of the whole for statistical analysis. The conclusion depends on many variables, including sample size, methods, variations within samples, and in the case of humans, gender, age, lifestyle, genes, environment, diet, stress, taste preferences… you get the idea.

You are unique in the history of the universe, while studies are mathematical representations of a group of numbers meant to represent reality. Where do you fit in the bell curve that represents “normal”? Is it good or bad to be “normal” if heart disease and cancer are the leading killers of Americans? It’s OK if you find all these limitations are too much. That’s what your doctors are for.

Should you like research, here’s how to view a study:

  • Always check the conclusion with common sense. If the analysis says gravity points downward, question it.
  • Consider the source: who is paying for this conclusion? If the study is funded by a special interest, double question it. Whom do the study authors work for? Can the funding source influence the study outcome?
  • Is there a potential for bias? Is there a hidden agenda? (Peridex did not appear to fund the two studies above.)
  • Weigh the study’s conclusion against your “True North”: that collection of personal belief and value systems that govern your behavior and health decisions. The best drug or nutritional solution, which one speaks to you? Surgery vs. Non-surgery solutions? Eat and live now and pay later, or be sensible now so you don’t have to pay later?

Studies necessarily need to break the complex topic of human health down to more
manageable pieces. Even more difficult is how to figure out where to put each dot before the outline of the elephant is known. Chapter 2 discuss Whole Health as a possible holistic model to re-assemble all the dissected parts and breathe life back into the Whole.

Studies don’t always come to the same conclusion. More studies and time are often needed for consensus conclusion that says the Earth is no longer flat. Meanwhile, you may be turning blue if doctors can act only with consensus and all the proof in hand.

Navigating A New Frontier

Finding answers to your health issues is like finding America before Christopher Columbus’ discovery. Some of what we know is true, and some not. There is no certainty ahead. “You can sail off the edge of the Earth if you keep going west.”

If the answer to your health problem lies in the New World, what should you do if the directions are still sketchy? There will be times when studies are not yet available, and doctors seeing patients will have to sail like Christopher Columbus before the New World is discovered, by a combination of what’s known, what’s now, and what does all this mean.

Oral-Systemic science is in the process of mapping out the new frontier of mouth-body connections. Where studies are not yet available, I will cite my own experience and share my view in My Points.

My Points are based on my clinical experience from listening to patient feedback after carrying out Whole Health recommendations. My Points do not constitute proof that I am right, nor am I offering medical advice with them. They are offered for consideration by you, your dentists and doctors, and for future studies to prove them right or wrong.

Dr. Liao’s Points:

1. A point or a view is not automatically wrong or invalid just because there is no research study on the subject yet. For example, I believe Impaired Mouth is the major source of most medical and dental problems.

2. Successful patient outcome is valid and should be respected rather than dismissed as “anecdotal” and without merit. WHY a case is successful? Learning from other people’s success can save much effort and waste.

3. Keep an open mind. Remember that what we know in our own heads may or may not be true or valid, or maybe outdated already.

4.. Keep asking WHY you have certain symptoms, and keep peeling back the onion layers with this question: “Is treatment addressing the cause behind my symptoms, or managing them?”

5. Compare studies’ conclusions to your common sense and value system to avoid unpleasant consequences or nasty surprises later.


1. Nagelberg RH, The Oral-Systemic Connection, www.Dental
2. Houston S. et. al, Effectiveness of 0.12% chlorhexidine gluconate oral rinse in reducing prevalence of nosocomial pneumonia in patients undergoing heart surgery, Am J Crit Care. 2002 Nov;11(6):567-70.

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