Dental health and dementia prevention (new study)

A recent study of nearly 1,200 adults found that people with higher blood levels of a compound their mouth and gut bacteria produce, imidazole propionate, had lower cognitive scores and higher levels of Alzheimer’s blood markers. It is one of several recent findings that have pulled the mouth into the conversation about the aging brain, alongside gum bacteria turning up inside Alzheimer’s brains and large studies tying gum disease to dementia risk. Underneath that science sits a practical question, which is whether the ordinary things people do for their teeth, brushing, flossing, mouthwash, fluoride, and increasingly a visit to a biological dentist, do anything for the brain. This article covers what the evidence shows, starting with the oral-brain link and then moving through the everyday questions.

A brief history. Cleaning the teeth is ancient, but the daily habits most people follow are surprisingly recent. The earliest tools were chew sticks, frayed twigs used by the Babylonians and Egyptians around 3500 BC, often taken from aromatic plants that also freshened the breath. The bristle brush came from China, where boar hairs were set into bone or bamboo handles several centuries ago, and it reached Europe by the late 1400s. Mass production began with William Addis in England around 1780, boar bristles gave way to nylon in 1938, and the twice-daily routine spread widely in the United States only after World War II, when returning soldiers brought the habit home. The decline in cavities across the twentieth century tracks the arrival of fluoride, in water from the 1940s and in toothpaste from the 1950s and 1960s, more closely than the spread of brushing itself, since brushing without fluoride does little against decay. Mouthwash took a different path. It began as a surgical antiseptic, and the version called Listerine was formulated in 1879 and named after the surgeon who pioneered antiseptic operating rooms. Its use as a daily rinse came later, driven by an advertising campaign in the 1920s that presented bad breath as a social problem to be treated, which is much of the reason so many people still reach for a rinse to feel fresh.

The evidence linking the mouth to the aging brain runs from a single trial down to animal models

Prevention evidence. The strongest study designs bear on prevention, where the evidence is thin. The only randomized trial to test the oral-brain link directly gave people with Alzheimer’s a drug meant to block gingipains, the toxic enzymes made by a common gum bacterium, and that trial did not meet its primary cognitive goal, though a subgroup with high levels of the bacterium showed slower decline. Below that tier sits observational prevention data. An analysis from the Atherosclerosis Risk in Communities study found regular flossing associated with lower incident dementia after adjusting for many factors including brushing habits and genetic risk, although this comes from a conference presentation rather than a full peer-reviewed report. No randomized trial has yet shown that treating gum disease or flossing prevents dementia, which leaves the prevention case resting on lower tiers of evidence.

Human population studies. A 2025 systematic review and meta-analysis pooling case-control and cohort studies found periodontitis, meaning advanced gum disease, associated with dementia at an odds ratio of about 2.26 and a hazard ratio of 1.15, with the signal concentrated in severe disease rather than mild gum inflammation. A ten-year study using Taiwan’s national insurance database found chronic periodontitis associated with roughly a 1.7-fold higher risk of later Alzheimer’s, and a systematic review of longitudinal studies reached a similar conclusion. The imidazole propionate finding from the opening adds a genetic layer to this, since an analysis using inherited gene variants within that study supported a causal direction rather than simple correlation. One real complication runs through all of it, which is that cognitive decline itself worsens oral hygiene, so part of the association likely runs backward. I covered microbiome testing and its brain connections in a previous article, and infection as a dementia risk factor in this one.

Tissue and animal mechanism. Examination of donated human brains in a 2019 study in Science Advances found the main gum-disease bacterium, Porphyromonas gingivalis, along with its gingipain enzymes, inside the brains of people who had Alzheimer’s, with enzyme levels tracking the amount of tau, one of the two hallmark Alzheimer’s deposits. Since mice do not brush their teeth or develop human gum disease on their own, researchers had to create the condition deliberately, and in that 2019 work they applied the bacterium into the mouths of mice every other day for six weeks to establish a lasting oral infection before looking for what reached the brain. Those mice developed brain colonization and more amyloid-beta, the other hallmark deposit, while a drug that blocked the gingipain enzymes reduced both. The mouse arm of the imidazole propionate work took the same deliberate approach from the other direction, giving the compound to animals directly and then measuring the brain, where it crossed into tissue and worsened amyloid and tau by damaging the blood-brain barrier, the lining that controls what passes from blood into the brain, and the same metabolite has been tied to Parkinson’s-like damage in mice carrying an oral bacterium. The reason for building these models is to test cause rather than association, since a human study can show that people with gum disease have more dementia but cannot rule out that the cognitive decline came first and led to worse oral care, whereas introducing a single microbe or compound and watching for brain changes tests whether that agent alone can produce them. That same design is why the results carry weight as mechanism and little as proof for people, both because no one can ethically assign a person to a gum infection and because many effects seen in mice have never reached humans.

The everyday questions have firmer answers than the dementia link does

Does the timing of brushing matter, and can three times a day harm enamel?

Frequency and timing. Brushing twice a day with fluoride has solid support, and the exact clock time matters less than the routine around it. A systematic review and meta-analysis in the Journal of Dental Research found that infrequent brushers had higher rates of new cavities, with roughly 1.45-fold higher odds for those brushing fewer than twice a day, and the authors noted that the twice-daily norm itself rests on a thinner evidence base than most people assume. The fluoride matters as much as the mechanical scrubbing. A Cochrane review of fluoride toothpaste found it reduced cavities by about a quarter compared with non-fluoride toothpaste, with twice-daily use adding further benefit. The specific idea that brushing last thing at night matters most rests mostly on physiology rather than head-to-head trials, since unstimulated saliva, which buffers acid and clears debris, falls to its lowest during sleep, so anything left on the teeth overnight sits there with less natural protection. A practical consequence is that brushing after the last food or drink of the evening fits the evidence better than brushing earlier and then eating, and a pre-going-out brush for a fresh mouth and a before-bed brush are not mutually exclusive.

Three times a day and enamel. Brushing three times a day carries little risk of wearing down enamel on its own, because the wear that toothbrushing can cause depends far more on how a person brushes than on how often. Reviews of toothbrush abrasion find that the main drivers of tooth-surface wear are the abrasiveness of the toothpaste, the force applied, and the stiffness of the bristles, with brushing frequency acting as a smaller multiplier on top of those. Enamel is hard and resists this wear well, so the loss that does occur shows up mostly at the gumline and on exposed root surfaces, where it contributes to the wedge-shaped notches known as non-carious cervical lesions rather than thinning the enamel on the biting surface. Two habits raise the risk more than frequency does, namely a high-abrasion whitening toothpaste, which can carry roughly double the abrasiveness of a standard paste, and brushing immediately after something acidic, which briefly softens the enamel. Both of these increase wear, which is one reason a gentle technique with a soft brush and a standard fluoride paste keeps three daily brushings low-risk.

Does the toothbrush itself matter, from electric versus manual to microplastics and boar bristle?

Electric versus manual. Electric toothbrushes carry a modest evidence edge over manual ones that matters most for people whose technique needs help. A Cochrane review of 56 randomized trials with more than 5,000 participants found that powered brushes reduced plaque by about 11 percent at one to three months and 21 percent after three months, and reduced gum inflammation by roughly 6 to 11 percent, with the oscillating-rotating type carrying the most evidence. The review also noted that the clinical importance of those differences is unclear, meaning the gap is measurable but not large. The practical advantage of a powered brush comes less from the motor than from the built-in timer and pressure sensor, which make it easier to brush for long enough and to ease off when pressing too hard, so it tends to help most for people who brush too briefly or too aggressively. Manual brushing reaches the same result when the technique is already good. One caveat ties back to the earlier point on abrasion, since laboratory simulations show powered brushes can wear the tooth surface faster than manual ones when paired with a firm hand and an abrasive paste, which is the situation the pressure sensor exists to prevent.

Microplastics and boar bristle. Plastic toothbrushes do shed microplastics into the mouth, though the connection to the brain is not established and the main exposure routes lie elsewhere. Microplastics have now been measured in human brain tissue. A 2025 study in Nature Medicine found them in the brain at higher concentrations than in the liver or kidney, rising in more recent samples, and present in greater amounts in the brains of people who had dementia, although the authors do not claim the plastics caused the dementia and other researchers have questioned how reliably the absolute amounts can be measured. I covered that study and my own plastic-reduction changes in Microplastics and the Brain. Laboratory work separately confirms that ordinary toothbrushes release microplastic fragments during brushing, with a survey of oral-care products estimating on the order of tens of particles per brushing from nylon bristles. What connects those two findings is not yet clear, because the plastic that dominates in brain tissue is polyethylene, whereas toothbrush bristles are mostly nylon and related polymers, and the quantified sources of human exposure are food, air, and drinking water, where switching from bottled to filtered tap water alone has been estimated to cut intake by roughly 90 percent. A natural-bristle brush, such as a boar-bristle one, does remove the nylon-shedding source, so as a low-cost precaution against that one contribution it is reasonable, though no evidence yet shows it changes the amount of plastic reaching the brain, and natural bristles tend to be firmer, which returns to the abrasion question above.

Which toothpaste helps, and does baking soda make a difference?

Baking soda. Baking soda toothpaste has a small measurable edge, mostly on plaque and stain. A systematic review found that baking soda toothpaste gave a small but statistically significant improvement in plaque removal in single-brushing studies, along with a small reduction in gum bleeding, and it has low abrasiveness. As long as it also contains fluoride, a baking soda paste is a reasonable default that keeps the cavity protection while adding that modest plaque advantage. Whitening toothpastes sit at the other end of the abrasiveness range and offer no cavity benefit over standard fluoride paste, which is the more consequential distinction between products than the presence of baking soda.

Does fluoride prevent cavities, and is it safe for the brain?

Cavities and the brain. The cavity-prevention benefit of fluoride toothpaste is one of the better-established findings in dentistry, shown across Cochrane reviews of fluoride toothpaste. The newer controversy concerns neurodevelopment. A 2024 National Toxicology Program monograph concluded with moderate confidence that fluoride above 1.5 milligrams per liter in water, roughly double the level recommended in United States drinking water, is associated with lower IQ in children, and stated there were insufficient data to determine whether the recommended 0.7 milligram level has any effect. A 2025 meta-analysis in JAMA Pediatrics synthesizing more than seventy studies reported an inverse association between fluoride and children’s IQ, with some signal appearing below 1.5 milligrams per liter in the higher-quality studies. Major dental and pediatric health bodies maintain that at the levels used in United States water there is no measurable effect on IQ, and have criticized the methods of the toxicology report. A distinction that often gets lost is that this debate concerns fluoride swallowed in water over years, which is a different exposure from topical fluoride in toothpaste that is spat out rather than ingested.

Should you use mouthwash, does it harm the helpful bacteria, and what keeps breath fresh?

The nitric oxide question. Antiseptic mouthwash kills bacteria without discriminating, including ones the body uses to regulate blood pressure. Certain bacteria on the back of the tongue convert dietary nitrate, from vegetables like beets and leafy greens, into nitrite, a building block the body turns into nitric oxide, a molecule that relaxes blood vessels. A review of this pathway describes how antiseptic rinses reduce these bacteria and lower nitric oxide, and observational data from an overweight-adult cohort found frequent over-the-counter mouthwash use associated with higher rates of high blood pressure and prediabetes. The controlled evidence for this effect is strongest for chlorhexidine, and the associations with blood pressure and blood sugar come from observational studies that cannot prove cause, so this reads as a reason for caution about reflexive daily antiseptic rinsing rather than an alarm. The effect on the bacteria also appears to be largely reversible once the rinse stops.

Chlorhexidine. It is a therapeutic rinse meant for a defined problem over a short course rather than an everyday product. A Cochrane review found high-quality evidence that chlorhexidine added to normal brushing produces a large reduction in plaque and a moderate reduction in gum inflammation. It also stains teeth with prolonged use, which is one reason it is typically prescribed for a defined period of around four weeks for a specific problem, such as after oral surgery or during active gum treatment, rather than used indefinitely. For that short-term, targeted use it is one of the more effective options available. As an everyday habit it carries the same nitric-oxide tradeoff described above along with the staining, for gum benefits that mechanical cleaning largely provides on its own, so the balance shifts against it when it is used continuously.

Whitening rinses. These are a separate, cosmetic category. The whitening rinses sold by major brands use hydrogen peroxide to lift surface stains and are not the same as the antiplaque and antigum-disease rinses that carry the trial evidence. Hydrogen peroxide is still a broad antibacterial agent, and it has been grouped with the ingredients that can affect the nitrate-reducing bacteria, so it is not clearly neutral for that pathway, only less studied. Because it is cosmetic and the whitening from a brief rinse is modest, it is the easiest rinse to use sparingly for anyone concerned about the microbiome question.

Staying fresh without it. Many people reach for mouthwash mainly to stay fresh, so the caution above about daily antiseptic rinsing raises a fair question about what to use instead. Most bad breath is a tongue-and-gum problem that responds to mechanical care more than to rinses, since around 80 to 90 percent of it comes from the mouth, mainly from a coated tongue and from gum disease, where bacteria produce the sulfur gases responsible for the smell. A Cochrane review of tongue scraping found a short-term reduction in those gases compared with a toothbrush, though the evidence was limited. Keeping saliva flowing through hydration, and reducing the bacterial fuel through good cleaning, address the main sources, and sugar-free gum or a drink of water stimulates saliva enough to cover the short-term freshness that sends people to the mouthwash bottle. Oral probiotics are a newer option, and a systematic review of randomized trials found that certain strains can reduce the sulfur gases and the bacteria that make them, with the caution that the trials are small. For anyone who still wants a rinse before a social occasion, an occasional non-antiseptic or plain-water rinse covers the moment without the daily-antiseptic tradeoff. Bad breath that persists despite good oral care is a reason to look for non-oral causes such as sinus drainage or reflux.

Does flossing do much for the gums?

Interdental cleaning. Flossing has the weakest evidence of the common habits, though it is not nothing. A 2019 Cochrane review of cleaning between the teeth found that flossing or interdental brushes, small brushes that fit between teeth, added to toothbrushing may reduce gum inflammation more than brushing alone, with the caveat that the evidence was low to very-low certainty and the effects may be small. The same review found that interdental brushes may work better than string floss where the gaps between teeth allow them. So flossing has a modest, low-certainty benefit for the gums, and the flossing-and-dementia signal mentioned earlier rests on a single observational analysis rather than anything stronger.

Do six-monthly cleanings prevent gum disease and bad bacteria?

The fixed schedule. The routine six-month cleaning is a standard part of dental care, and the evidence supporting a fixed interval for everyone is limited. A Cochrane review of routine scale and polish in adults without severe gum disease found that scheduled scale-and-polish treatments made little or no difference to gum inflammation, gum-pocket depth, or quality of life over two to three years compared with no scheduled cleaning, with high-certainty evidence. A separate Cochrane review of recall intervals, drawing on a four-year randomized trial of more than 2,000 adults, found little to no difference in gum bleeding between six-month, two-year, and risk-based recall schedules. What the cleaning does reliably do is remove calculus, the hardened tartar that brushing cannot reach and that harbors bacteria, so it lowers the bacterial reservoir, though the biofilm rebuilds continuously and daily home care is what keeps it in check between visits. The practical reading is that a fixed six-month cleaning is not a strong independent lever for preventing gum disease in a healthy mouth, and matching the interval to a person’s actual risk works as well. The picture is different for someone who already has periodontitis, where professional periodontal treatment and ongoing maintenance do slow the disease and are well supported.

Deep cleaning is a different procedure. A routine cleaning and a deep cleaning are often confused, and they are not the same thing. A routine cleaning, sometimes called a prophylaxis, is a preventive scale-and-polish above the gumline for a mouth without gum disease. A deep cleaning, known as scaling and root planing, reaches below the gumline to remove the bacterial film and hardened tartar from the deeper pockets that form once gum disease has set in, and the name reflects the fact that those pockets are physically deeper. For someone who has periodontitis, the evidence for it is good. A systematic review of below-the-gumline instrumentation found that it reduced gum-pocket depth by around 1.4 millimeters over six to eight months and closed most of the treated pockets, and it is the standard non-surgical treatment before any surgical options are considered. The distinction that matters is diagnostic rather than a question about the procedure. A deep cleaning is a treatment for measured disease, meaning gum pockets, bleeding, and bone loss visible on an X-ray, rather than a preventive step for a healthy mouth or mild gum inflammation, where a routine cleaning and better home care are the appropriate response. When the diagnosis fits, the treatment is well supported, and the useful questions for anyone told they need one are what the pocket-depth readings were and whether they point to gum disease.

What is behind the biological dentistry craze, and what does it cost?

What it is. I first learned the phrase “Biological Dentistry” last year at the Longevity Clinical Roundtable at the Buck and have been wondering about it ever since. Biological dentistry, also called holistic dentistry, is an approach that treats the mouth as connected to whole-body health and favors biocompatible materials, mercury-free and often fluoride-free care, and methods such as ozone therapy over conventional protocols. It has grown noticeably more popular in longevity and wellness circles over the past few years, promoted by many of the same voices that advocate for continuous glucose monitors, oral microbiome testing, and environmental-toxin avoidance, and often presented as the brain-conscious way to care for teeth. That framing is one reason to examine it on its own terms rather than dismiss it out of hand.

The contested positions. The field blends some evidence-aligned ideas with a few positions that run ahead of the evidence. The core framing, that oral health connects to whole-body health, is reasonable and matches much of the research above, and several of its practices, including minimally invasive fillings, biocompatible materials, and attention to the oral microbiome, sit comfortably with mainstream science. Two of its signature positions are more contested. The avoidance of fluoride draws on the high-exposure neurodevelopment research described earlier, but extends it into blanket avoidance of topical fluoride toothpaste, which is a different and much lower exposure than fluoridated water. The preference for removing or avoiding root canals traces to the focal infection theory from the early twentieth century, associated with work in which root-canal-treated teeth implanted under the skin of rabbits were taken as evidence that such teeth cause disease elsewhere in the body. That theory was largely set aside by the mid-twentieth century as immunology and research methods advanced, and current evidence does not support the idea that a properly treated root canal causes systemic illness.

Cost and insurance. The cost question usually comes down to network status and which services are covered. Biological and holistic practices are often fee-for-service and out-of-network, meaning patients frequently pay upfront and seek partial reimbursement rather than having the office bill insurance directly. Routine covered procedures such as exams and cleanings can still be reimbursed through out-of-network benefits, so it is not necessarily all out of pocket, but the signature services tend not to be covered. Safe amalgam removal protocols, ozone treatment, oral microbiome testing, and metal-free zirconia implants generally fall outside insurance, and implants are expensive regardless of the practice, commonly several thousand dollars each, with the metal-free ceramic versions running somewhat higher than titanium. Because annual dental insurance maximums are low, often between one and two thousand dollars, any large procedure leaves a substantial out-of-pocket balance in a conventional or a biological office alike.

The practical takeaways. What the evidence supports comes down to a set of unglamorous habits, none of which depends on the dementia claim being proven.

• Brushing twice a day, and ideally after the last food or drink of the evening, covers the timing that matters, and a third brushing is low-risk when done gently with a soft brush and a non-whitening paste rather than right after acidic food.

• An oscillating-rotating electric brush has a modest edge and helps most for people who brush too briefly or too hard, while a manual brush reaches the same result with good technique.

• A baking soda fluoride toothpaste is a good default, since it holds a small edge on plaque over standard fluoride paste while keeping the fluoride that prevents cavities, whereas whitening pastes add abrasion without a cavity benefit.

• Fluoride toothpaste prevents cavities, and the neurodevelopment debate concerns fluoride swallowed in water over years rather than the topical paste that is spat out.

• A non-plastic, natural-bristle toothbrush removes one microplastic source, with the caveat that its effect on the body’s overall plastic load is unproven and that firmer natural bristles reward a gentle technique.

• Cleaning between the teeth, whether with floss or interdental brushes, adds a modest benefit for the gums.

• Mouthwash is best kept occasional rather than reflexive, with antiseptic rinses like chlorhexidine reserved for a specific reason and short course.

• Fresher breath comes from treating the source, through tongue cleaning and good oral hygiene, more than from a daily rinse.

• Biological dentistry’s whole-body framing is reasonable, but blanket fluoride avoidance and routine root-canal removal run ahead of the evidence, and its signature services are largely out of pocket.

• Professional cleaning removes tartar that brushing cannot and matters most for people who already have gum disease, while for a healthy mouth the evidence supports matching the visit interval to individual risk rather than a fixed six months.

Summary. The oral-brain connection is a real and active area of research, strongest as association and biological mechanism and weakest exactly where it would matter most, on whether cleaning up the mouth prevents dementia. The coming years of intervention trials, including the microbiome work I have written about elsewhere, will settle how much of the mechanism translates into prevention that a person can act on. Excellent oral hygiene carries almost no downside and protects the teeth and gums, along with the cardiovascular health they connect to, regardless of how the dementia question resolves, so there is little to lose in keeping it up while the evidence is still coming in.