When I graduated from dental school, nobody talked about the oral microbiome. It wasn’t in the curriculum. It wasn’t in the journals. The prevailing theory — the one we were all taught as settled science — was that cavities were caused by a single bacterium: Streptococcus mutans. One bug. One culprit.
Scientists were so confident in this that by the mid-1970s, they were developing a vaccine against it.
The vaccine never worked.
And we now know why: the premise was completely wrong.
Cavities aren’t caused by one rogue bacterium. They’re caused by an ecosystem falling out of balance. And treating that ecosystem like a battlefield — carpet-bombing it with antiseptic rinse, declaring war on every microbe in sight — wasn’t solving the problem. It was making it worse.
I’m not blaming my professors. They taught me what was known. The problem is what wasn’t known yet — and how long it’s taken dentistry as a profession to catch up with what the science is now showing us.
Here’s what I wish I’d learned on day one:
Your mouth isn’t dirty. It’s alive.
It’s an ecosystem of around 700 bacterial species, most of them working for you. They regulate the acidity of your mouth. They help manage your blood pressure — your body actually outsourced the job of converting dietary nitrate into nitric oxide to your oral bacteria, because we don’t have the enzymes to do it ourselves. They protect your gums. They are, in every meaningful sense, part of you.
And they are in constant conversation with the rest of your body. When your gums bleed — even just a little — that’s not simply a sign you need to floss more. It’s an open doorway where bacteria can enter your bloodstream and travel to every other system.
The implications of that single fact are staggering.
Fusobacterium nucleatum — an oral bacterium — has been found inside colorectal tumors. Porphyromonas gingivalis, the primary driver of gum disease, has been detected in the brains of people with Alzheimer’s. People with periodontal disease have significantly higher rates of cardiovascular disease and inflammatory bowel disease.
Both of my parents had Alzheimer’s. Every time a new study links oral pathogens to cognitive decline, I feel it in my chest. It’s part of why I can’t stop talking about this.
I’ve been saying this for decades, long before the research was there to back me up. And I’ll be honest: there were years when I wondered if I was the one who had it wrong. I wasn’t.
But dentistry is still catching up — and in the meantime, there are things you can start doing today that most dentists still aren’t telling you.
First things first: I’m begging you to stop carpet-bombing your mouth.
Remember those TV ads showing blue liquid swirling through the mouth, killing everything in its path? That was the promise of mouthwash. Clean. Disinfected. Bacteria-free.
That was exactly the wrong goal.
There’s a group of bacteria living on your tongue called nitrate-reducing bacteria. They convert nitrates from foods like beets, spinach, and arugula into nitric oxide — the molecule your body uses to keep blood vessels relaxed and blood pressure regulated. Mouthwash wipes them out indiscriminately.
There’s a study I genuinely haven’t stopped thinking about since I first read it. Researchers gave older adults beet juice to lower their blood pressure — and it worked. Unless they’d been rinsing with antiseptic mouthwash. Then the blood pressure benefit completely disappeared.
The largest longitudinal study on this — 945 adults tracked over three years at Harvard and the University of Puerto Rico — found that using over-the-counter mouthwash twice a day was associated with a 55% increased risk of prediabetes and a significant increase in hypertension risk, independent of diet, exercise, weight, and every other major variable the researchers measured (Joshipura et al., Nitric Oxide, 2017; Blood Pressure, 2020).
And in 2024, Listerine’s own manufacturer funded a study describing their product as “non-selectively resetting” the oral microbiome. They framed that as a positive. But “non-selective” means it can’t tell the difference between the bacteria causing your gum disease and the bacteria protecting your cardiovascular system.
Less destructive is not the same as safe.
If your dentist tells you the concern only applies to prescription chlorhexidine rinse, ask them about the SOALS study.
This goes so much deeper than mouthwash.
What I was never taught in dental school — and what I’ve spent decades learning through research and, frankly, through personal loss — is that your mouth is in constant conversation with your entire body. The oral microbiome is the headwaters of the gut microbiome. What happens in the mouth doesn’t stay in the mouth.
The brain changes associated with Alzheimer’s at 75 begin at 40. The cardiovascular disease diagnosed at 60 has roots that reach back decades. And the oral microbiome is woven into both of those timelines in ways we are only beginning to fully understand.
Nature, one of the most rigorous scientific journals in the world — ran a feature in 2021 with the headline: “Oral Microbiome Findings Challenge Dentistry Dogma.” The piece described researchers who spent their careers being told that oral biofilms were always bad, always to be eliminated, only to discover that in a healthy mouth, biofilm is protective. That the goal was never to eliminate bacteria but to cultivate the right ones.
The future of dentistry — and I mean this — is the dentist who sits across from you and says: let’s look at what’s actually living in your mouth, and let’s figure out what it’s telling us about the rest of your body. It’s why I’m a scientific advisor for this oral microbiome test (code DRB for 10% off). Targeted probiotic interventions are coming. The drill-fill-bill model is on its way out.
I just wish it would hurry up.
My daily non-negotiables
Ditch the mouthwash. All of it — even the “natural” ones, which typically contain essential oils that are just as disruptive to the oral microbiome as their conventional counterparts. Rinse with coconut oil instead—I love the taste and feel of this oil pulling blend.
Tongue scrape every morning. Your tongue harbors the biofilm where those critical nitrate-reducing bacteria live. Scraping removes harmful buildup without destroying the ecosystem. I use this stainless steel one, but any stainless steel scraper works.
Drink green tea between meals. The polyphenols thin biofilm without disrupting the beneficial bacteria and actively support your nitrate-reducing community. This is the one I drink daily.
Eat for your oral microbiome. Nitrate-rich greens — arugula, beets, spinach. Fermented foods — yogurt, kefir, sauerkraut (I’m a big sauerkraut fan personally). Polyphenol-rich foods — berries, cacao, pomegranate. These feed the bacteria that protect your gums, your cardiovascular system, and your brain.
Breathe through your nose. Day and night. Nasal breathing keeps saliva flowing, and saliva is your mouth’s natural defense system. If you snore, wake up with dry mouth, or suspect your airway is compromised, please find a sleep dentist through AADSM.org or a myofunctional therapist through our Functional Dentist Directory. This is one of the most overlooked — and most consequential — things I can point you toward.
And if you’re ready to go deeper: add an oral probiotic with Streptococcus salivarius strains to help repopulate your mouth with beneficial bacteria.
Why does any of this matter?
Because the science is telling us what I’ve believed for decades but couldn’t always prove: your mouth is the front door to your entire body’s health. This isn’t about avoiding cavities. It’s about blood pressure. Brain health. Independence at 80. The quality of the decades ahead of you. And, yet, we have somehow been led to believe that dentistry is just about a “pretty smile.” 😩
If you want a dentist who actually understands the oral-systemic connection — someone who will look at your mouth and think about your whole body — that’s exactly what my Functional Dentist Directory is for.
-Mark
Further Reading & Citations
Campbell, K. (2021). “Oral microbiome findings challenge dentistry dogma.” Nature Outlook: Oral Health. The piece that vindicates everything functional dentists have been saying for decades — published in one of the world’s most rigorous scientific journals. The S. mutans vaccine story alone is worth the read. Read it here.
Joshipura, K.J. et al. (2017). “Over-the-counter mouthwash use and risk of pre-diabetes/diabetes.” Nitric Oxide, 71, 14–20. Joshipura, K.J. et al. (2020). “Over-the-counter mouthwash use, nitric oxide and hypertension risk.” Blood Pressure, 29(2), 103–112. The SOALS study — 945 adults, three-year follow-up, Harvard and the University of Puerto Rico. The foundational research behind the mouthwash section of this newsletter. Two papers from the same cohort, both worth bookmarking. Critically, this research studied over-the-counter mouthwash — not prescription chlorhexidine — and measured real health outcomes over years, not a single biomarker over hours. Read the 2017 paper here. Read the 2020 paper here.
Bescos, R. et al. (2020). “Effects of chlorhexidine mouthwash on the oral microbiome.” Scientific Reports, 10, 5254. A controlled crossover study showing that 7 days of chlorhexidine mouthwash caused a major shift in the salivary microbiome, reduced the mouth’s ability to convert dietary nitrate to nitrite, lowered plasma nitrite levels, and was followed by a trend toward increased systolic blood pressure in healthy individuals. This is the mechanistic link between mouthwash, microbiome disruption, and cardiovascular risk made visible in real human subjects. Read it here.
Tribble, G.D. et al. (2019). “Frequency of Tongue Cleaning Impacts the Human Tongue Microbiome Composition and Enterosalivary Circulation of Nitrate.” Frontiers in Cellular and Infection Microbiology, 9:39. The study that connects your tongue scraper to your blood pressure. Researchers found that people with higher levels of nitrate-reducing bacteria on their tongues had measurably lower resting systolic blood pressure — and that regular tongue cleaning was a significant predictor of tongue microbiome composition. Managing the tongue microbiome isn’t just about fresh breath. Read it here.
Loughman, A., Adler, C.J., & Macpherson, H. (2023). “Unlocking Modifiable Risk Factors for Alzheimer’s Disease: Does the Oral Microbiome Hold Some of the Keys?” Journal of Alzheimer’s Disease, 92(1), 1–26. A rigorous review proposing a framework for how the oral microbiome interacts with every major modifiable risk factor for Alzheimer’s — including blood pressure, sleep, glucose regulation, and physical activity. The connection between oral nitrate-reducing bacteria and cardiovascular fitness alone makes this essential reading. Read it here.
Giordano-Kelhoffer, B. et al. (2022). “Oral Microbiota, Its Equilibrium and Implications in the Pathophysiology of Human Diseases: A Systematic Review.” Biomedicines, 10(8), 1803. A systematic review of 79 peer-reviewed studies examining the oral microbiome’s role in cardiovascular disease, neurodegeneration, and Alzheimer’s. Particularly useful for understanding the mechanisms behind the associations — not just the associations themselves. Read it here.
Frontiers in Cellular and Infection Microbiology (2025). “Oral microbiota in cardiovascular health and disease.” One of the most current overviews of how specific periodontal pathogens — including P. gingivalis and F. nucleatum — contribute to hypertension, atherosclerosis, and myocardial infarction risk. The research has moved well beyond association; it is now describing precise inflammatory mechanisms. Read it here.
Nelson-Dooley, C. (2019). Heal Your Oral Microbiome: Balance and Repair Your Mouth Microbes to Improve Gut Health, Reduce Inflammation and Fight Disease. Ulysses Press. The only book written specifically about the oral microbiome for a general audience — accessible, rigorously sourced, and practical. I believe it should be required reading in dental schools. If this newsletter sparked something for you and you want to go deeper, start here. Find it here.
Your mouth is killing you (literally)