Rare mineral from rocks found in mollusk teeth

Northwestern University researchers have, for the first time, discovered a rare mineral hidden inside the teeth of a chiton, a large mollusk found along rocky coastlines. Before this strange surprise, the iron mineral, called santabarbaraite, only had been documented in rocks.

The new finding helps understand how the whole chiton tooth -- not just the ultrahard, durable cusp -- is designed to endure chewing on rocks to feed. Based on minerals found in chiton teeth, the researchers developed a bio-inspired ink for 3D printing ultrahard, stiff and durable materials.

"This mineral has only been observed in geological specimens in very tiny amounts and has never before been seen in a biological context," said Northwestern's Derk Joester, the study's senior author. "It has high water content, which makes it strong with low density. We think this might toughen the teeth without adding a lot of weight."

The study will be published the week of May 31 in the Proceedings of the National Academy of Sciences.

Joester is an associate professor of materials science and engineering in Northwestern's McCormick School of Engineering. Linus Stegbauer, a former postdoctoral fellow in Joester's laboratory, is the paper's first author. At Northwestern during the research, Stegbauer is now a principal investigator at the Institute of Interfacial Process Engineering and Plasma Technology of the University of Stuttgart in Germany.

One of the hardest known materials in nature, chiton teeth are attached to a soft, flexible, tongue-like radula, which scrapes over rocks to collect algae and other food. Having long studied chiton teeth, Joester and his team most recently turned to Cryptochiton stelleri, a giant, reddish-brown chiton that is sometimes affectionately referred to as the "wandering meatloaf."

To examine a tooth from Cryptochiton stelleri, Joester's team collaborated with Ercan Alp, a senior scientist at Argonne National Laboratory's Advanced Photon Source, to use the facility's synchrotron Mössbauer spectroscopy as well as with Paul Smeets to use transmission electron microscopy at the Northwestern University Atomic and Nanoscale Characterization and Experiment (NUANCE) Center. They found santabarbaraite dispersed throughout the chiton's upper stylus, a long, hollow structure that connects the head of the tooth to the flexible radula membrane.

"The stylus is like the root of a human tooth, which connects the cusp of our tooth to our jaw," Joester said. "It's a tough material composed of extremely small nanoparticles in a fibrous matrix made of biomacromolecules, similar to bones in our body."

Joester's group challenged itself to recreate this material in an ink designed for 3D printing. Stegbauer developed a reactive ink comprising iron and phosphate ions mixed into a biopolymer derived from the chitin. Along with Shay Wallace, a Northwestern graduate student in Mark Hersam's laboratory, Stegbauer found that the ink printed well when mixed immediately before printing.

"As the nanoparticles form in the biopolymer, it gets stronger and more viscous. This mixture can then be easily used for printing. Subsequent drying in air leads to the hard and stiff final material," Joester said. Joester believes we can continue to learn from and develop materials inspired by the chiton's stylus, which connects ultra-hard teeth to a soft radula.

"We've been fascinated by the chiton for a long time," he said. "Mechanical structures are only as good as their weakest link, so it's interesting to learn how the chiton solves the engineering problem of how to connect its ultrahard tooth to a soft underlying structure. This remains a significant challenge in modern manufacturing, so we look to organisms like the chiton to understand how this is done in nature, which has had a couple hundred million years of lead time to develop."

The study, "Persistent polyamorphism in the chiton tooth: From a new biomaterial to inks for additive manufacturing," was supported by the National Science Foundation (award numbers DMR-1508399 and DMR-1905982), National Institutes of Health (award number NIH-DE026952), Air Force Research Laboratory (award number FA8650-15-2-5518) and Deutsche Forschungsgemeinschaft (award number STE2689/1-1).

Predicting tooth loss

Tooth loss is often accepted as a natural part of aging, but what if there was a way to better identify those most susceptible without the need for a dental exam?

New research led by investigators at Harvard School of Dental Medicine suggests that machine learning tools can help identify those at greatest risk for tooth loss and refer them for further dental assessment in an effort to ensure early interventions to avert or delay the condition.

The study, published June 18 in PLOS ONE, compared five algorithms using a different combination of variables to screen for risk. The results showed those that factored medical characteristics and socioeconomic variables, such as race, education, arthritis, and diabetes, outperformed algorithms that relied on dental clinical indicators alone.

"Our analysis showed that while all machine-learning models can be useful predictors of risk, those that incorporate socioeconomic variables can be especially powerful screening tools to identify those at heightened risk for tooth loss," said study lead investigator Hawazin Elani, assistant professor of oral health policy and epidemiology at HSDM.

The approach could be used to screen people globally and in a variety of health care settings even by non-dental professionals, she added.

Tooth loss can be physically and psychologically debilitating. It can affect quality of life, well-being, nutrition, and social interactions. The process can be delayed, even prevented, if the earliest signs of dental disease are identified, and the condition treated promptly. Yet, many people with dental disease may not see a dentist until the process has advanced far beyond the point of saving a tooth. This is precisely where screening tools could help identify those at highest risk and refer them for further assessment, the team said.

In the study, the researchers used data comprising nearly 12,000 adults from the National Health and Nutrition Examination Survey to design and test five machine-learning algorithms and assess how well they predicted both complete and incremental tooth loss among adults based on socioeconomic, health, and medical characteristics.

Notably, the algorithms were designed to assess risk without a dental exam. Anyone deemed at high risk for tooth loss, however, would still have to undergo an actual exam, the researchers added.

The results of the analysis point to the importance of socioeconomic factors that shape risk beyond traditional clinical indicators.

"Our findings suggest that the machine-learning algorithm models incorporating socioeconomic characteristics were better at predicting tooth loss than those relying on routine clinical dental indicators alone," Elani said. "This work highlights the importance of social determinants of health. Knowing the patient's education level, employment status, and income is just as relevant for predicting tooth loss as assessing their clinical dental status."

Indeed, it has long been known that low-income and marginalized populations experience a disproportionate share of the burden of tooth loss, likely due to lack of regular access to dental care, among other reasons, the team said.

"As oral health professionals, we know how critical early identification and prompt care are in preventing tooth loss, and these new findings point to an important new tool in achieving that," said Jane Barrow, associate dean for global and community health and executive director of the Initiative to Integrate Oral Health and Medicine at HSDM. "Dr. Elani and her research team shed new light on how we can most effectively target our prevention efforts and improve quality of life for our patients."

The research was done in collaboration with researchers at the Harvard T.H. Chan School of Public Health, the University of São Paolo in Brazil, and the University of Otago Faculty of Dentistry in New Zealand.

Co-investigators included André F. M. Batista, W. Murray Thomson, Ichiro Kawachi, and Alexandre D. P. Chiavegatto Filho.

This work was supported by the National Institute on Minority Health And Health Disparities (grant K99MD012253) and CNPq (grant 308731/2018-2).

A link between childhood stress and early molars

Early in her career neuroscientist Allyson Mackey began thinking about molars. As a researcher who studies brain development, she wanted to know whether when these teeth arrived might indicate early maturation in children.

"I've long been concerned that if kids grow up too fast, their brains will mature too fast and will lose plasticity at an earlier age. Then they'll go into school and have trouble learning at the same rate as their peers," says Mackey, an assistant professor in the Department of Psychology at Penn. "Of course, not every kid who experiences stress or [is] low income will show this pattern of accelerated development."

In the Proceedings of the National Academy of Sciences, Mackey, with doctoral student Cassidy McDermott and colleagues from Penn's School of Dental Medicine and the University of Missouri-Kansas City, shows that children from lower-income backgrounds and those who go through greater adverse childhood experiences get their first permanent molars earlier. The findings, generated initially from a small study and replicated using a nationally representative dataset, align with a broader pattern of accelerated development often seen under conditions of early-life stress.

"It's really important for us to understand how to detect early maturation sooner," Mackey says. "Right now, we're relying on seeing when kids hit puberty, which might be too late for some meaningful interventions. If we can inexpensively see that a child is experiencing this maturation earlier, we might be able to direct more intervention resources toward them."

A novel rating system

Broadly speaking, Mackey's lab studies how the brain changes and grows as people learn. It's well-established that stress during childhood speeds up maturation and that children who hit puberty earlier are at greater risk for both physical and mental health problems in adulthood.

Beyond that, in studies across primate species, molar eruption has been used to measure childhood length and correlates with a number of other developmental events. Similarly, for humans, the timing of dental events often plays a role in estimating biological age.

"That all made molar eruption a compelling developmental indicator," says McDermott, who is training to be a clinical psychologist.

It helped that more than 100 children, ages 4 to 7, had been participating in two Penn brain development studies, which included structural and functional MRI scans. "There's one type of MRI scan called a T2 weighted scan where you can visualize the morphology of the tooth pretty well," McDermott says. These scans -- typically used to look at the brain -- showed the researchers just how close these molars were to breaking through the gum line.

Once Mackey and McDermott realized this, they partnered with Katherine Hilton, then a student in Penn Dental Medicine, and Muralidhar Mupparapu, a professor in the Department of Oral Medicine, who developed a novel scale to precisely rate each tooth's position.

"The scale ranges from 1 to 4," McDermott says. "At the low end of the scale is 1, which is before the tooth has really developed at all. As the tooth emerges, there are intermediate stages, and the highest rating, a 4, is when the tooth is fully in the mouth and parallel with the other teeth." Four molars each received a score, which then got averaged, leaving a single score per individual.

Controlling for factors like age and gender, the researchers then looked for associations between early environment and molar eruption. "What we found is that income and adverse childhood experiences are both individually associated with molar eruptions status," McDermott says.

Replicating the findings

Those findings derived from just 117 participants, so although the correlation was clear, Mackey and McDermott hoped to replicate what they'd seen.

Collaborators at the University of Missouri-Kansas City told them about a large population-representative dataset called the National Health and Nutrition Examination Survey (NHANES), which is publicly available and includes dental data, demographic data, and family income, among other measures.

"Because our sample is only from one city and is much smaller than a population-representative study like that," McDermott says, "we saw it as an opportunity to verify that the findings exist outside of what we had collected in Philadelphia."

Though some facets differed -- NHANES measures dental development a little differently, for example -- the models showed similar results, indicating a connection between lower family income and earlier first molars.

Whether this overall trend is new or just now coming to light is something Mackey wants to study further. She's also curious about when the rate of maturation gets set. "Is it as early as in utero or is it dynamically adjusted based on stressors in the world?" she says. "If it's the latter, that tells you there are more opportunities to intervene."

Present implications, future work

There are still significant unknowns, as well as findings that need further examination, Mackey says. For example, the research team found racial disparities in this timing, with first molars emerging in Black children sooner than in white children.

"These race differences in molar eruption have been known for a long time, but no one thought critically about where they came from," she says. "It's consistent with higher levels of stress due to structural racism. This is a clear indication that it's not just speculation that experiences with racism can cause stress and early aging. They are having an effect on kids that we can't ignore."

For all children, a year-plus of pandemic-driven grief and social isolation most certainly amplified stress levels, making it even more important to understand who is at greatest risk for early maturation, Mackey says.

Yet she and McDermott emphasize that molar timing shouldn't become another parental fear. "What I really don't want is for parents to either worry or feel complacent just based on when their kids got their molars," says Mackey. "We don't have those data yet."

The Penn researchers are working on it. In the future, they hope to collaborate with dental offices to recruit children into studies based on their molar-eruption status. The goal would be to follow them into adulthood, to get more information on what precisely early first molars may indicate. "If this is the meaningful discovery that I think it is," Mackey says, "I would love for many scientists to jump on board and test these hypotheses."

Funding for this research came from the Jacobs Foundation, National Institute on Drug Abuse (Grant 1R34DA050297-01), and National Science Foundation.What would help, she thought, was a scalable, objective way -- a physical manifestation, of sorts -- to indicate how children embodied and responded to stresses in their world. Eruption timing of the first permanent molars proved to be just that.

Could Losing Your Wisdom Teeth Enhance Your Sense of Taste?

So claims a new study that challenges previous research on the issue.

"Prior studies have only pointed to adverse effects on taste after extraction, and it has been generally believed that those effects dissipate over time," said study senior author Richard Doty. He is director of the Smell and Taste Center at the University of Pennsylvania, in Philadelphia.

"This new study shows us that taste function can actually slightly improve between the time patients have surgery and up to 20 years later," Doty said in a Penn Medicine news release. "It's a surprising but fascinating finding that deserves further investigation to better understand why it's enhanced and what it may mean clinically."

For the study, the investigators analyzed data from 1,255 people who were evaluated at the smell and taste center over 20 years. Of those, 891 had undergone wisdom tooth extraction and 364 had not.

The participants were tested on their ability to detect sweet, salty, sour or bitter tastes. For all four tastes, the wisdom tooth extraction group outperformed the control group, according to the study published recently in the journal Chemical Senses.

People who've had wisdom teeth extracted typically have an average 3% to 10% long-term improvement in their ability to taste, the researchers concluded.

There are two possible explanations, the study authors suggested.

Wisdom tooth extraction may damage nerves that control taste buds in the front of the mouth, which releases restrictions on nerves that control taste buds in the back of the mouth, boosting whole-mouth sensitivity.

The second possibility is that nerve damage from wisdom tooth extraction may cause taste hypersensitivity, according to the report.

"Further studies are needed to determine the mechanism or mechanisms behind the extraction-related improvement in taste function," Doty said. "The effects are subtle, but may provide insight into how long-term improvement in neural function can result from altering the environment in which nerves propagate."

How teeth sense the cold

"It's a unique kind of pain," says David Clapham, vice president and chief scientific officer of the Howard Hughes Medical Institute (HHMI). "It's just excruciating."

Now, he and an international team of scientists have figured out how teeth sense the cold and pinpointed the molecular and cellular players involved. In both mice and humans, tooth cells called odontoblasts contain cold-sensitive proteins that detect temperature drops, the team reports March 26, 2021, in the journal Science Advances. Signals from these cells can ultimately trigger a jolt of pain to the brain.

The work offers an explanation for how one age-old home remedy eases toothaches. The main ingredient in clove oil, which has been used for centuries in dentistry, contains a chemical that blocks the "cold sensor"protein, says electrophysiologist Katharina Zimmermann, who led the work at Friedrich-Alexander University Erlangen-Nürnberg in Germany.

Developing drugs that target this sensor even more specifically could potentially eliminate tooth sensitivity to cold, Zimmermann says. "Once you have a molecule to target, there is a possibility of treatment."

Mystery channel

Teeth decay when films of bacteria and acid eat away at the enamel, the hard, whitish covering of teeth. As enamel erodes, pits called cavities form. Roughly 2.4 billion people -- about a third of the world's population -- have untreated cavities in permanent teeth, which can cause intense pain, including extreme cold sensitivity.

No one really knew how teeth sensed the cold, though scientists had proposed one main theory. Tiny canals inside the teeth contain fluid that moves when the temperature changes. Somehow, nerves can sense the direction of this movement, which signals whether a tooth is hot or cold, some researchers have suggested.

"We can't rule this theory out," but there wasn't any direct evidence for it, says Clapham a neurobiologist at HHMI's Janelia Research Campus. Fluid movement in teeth -- and tooth biology in general -- is difficult to study. Scientists have to cut through the enamel -- the hardest substance in the human body -- and another tough layer called dentin, all without pulverizing the tooth's soft pulp and the blood vessels and nerves within it. Sometimes, the whole tooth "will just fall to pieces," Zimmermann says.

Zimmerman, Clapham, and their colleagues didn't set out to study teeth. Their work focused primarily on ion channels, pores in cells' membranes that act like molecular gates. After detecting a signal -- a chemical message or temperature change, for example -- the channels either clamp shut or open wide and let ions flood into the cell. This creates an electrical pulse that zips from cell to cell. It's a rapid way to send information, and crucial in the brain, heart, and other tissues.

About fifteen years ago, when Zimmermann was a postdoc in Clapham's lab, the team discovered that an ion channel called TRPC5 was highly sensitive to the cold. But the team didn't know where in the body TRPC5's cold-sensing ability came into play. It wasn't the skin, they found. Mice that lacked the ion channel could still sense the cold, the team reported in 2011 in the journal Proceedings of the National Academy of Sciences.

After that, "we hit a dead end," Zimmermann says. The team was sitting at lunch one day discussing the problem when the idea finally hit. "David said, 'Well, what other tissues in the body sense the cold?' Zimmermann recalls. The answer was teeth.

The whole tooth

TRPC5 does reside in teeth -- and more so in teeth with cavities, study coauthor Jochen Lennerz, a pathologist from Massachusetts General Hospital, discovered after examining specimens from human adults.

A novel experimental set up in mice convinced the researchers that TRPC5 indeed functions as a cold sensor. Instead of cracking a tooth open and solely examining its cells in a dish, Zimmermann's team looked at the whole system: jawbone, teeth, and tooth nerves. The team recorded neural activity as an ice-cold solution touched the tooth. In normal mice, this frigid dip sparked nerve activity, indicating the tooth was sensing the cold. Not so in mice lacking TRPC5 or in teeth treated with a chemical that blocked the ion channel. That was a key clue that the ion channel could detect cold, Zimmermann says. One other ion channel the team studied, TRPA1, also seemed to play a role.

The team traced TRPC5's location to a specific cell type, the odontoblast, that resides between the pulp and the dentin. When someone with a a dentin-exposed tooth bites down on a popsicle, for example, those TRPC5-packed cells pick up on the cold sensation and an "ow!" signal speeds to the brain.

That sharp sensation hasn't been as extensively studied as other areas of science, Clapham says. Tooth pain may not be considered a trendy subject, he says, "but it is important and it affects a lot of people."

Zimmermann points out that the team's journey towards this discovery spanned more than a decade. Figuring out the function of particular molecules and cells is difficult, she says. "And good research can take a long time."

People with severe gum disease may be twice as likely to have increased blood pressure

Adults with periodontitis, a severe gum infection, may be significantly more likely to have higher blood pressure compared to individuals who had healthy gums, according to new research published today in Hypertension, an American Heart Association journal.

Previous studies have found an association between hypertension and periodontitis, however, research confirming the details of this association is scarce. Periodontitis is an infection of the gum tissues that hold teeth in place that can lead to progressive inflammation, bone or tooth loss. Prevention and treatment of periodontitis is cost effective and can lead to reduction of systemic markers of inflammation as well as improvement in function of the endothelium (thin membrane lining the inside of the heart and blood vessels).

"Patients with gum disease often present with elevated blood pressure, especially when there is active gingival inflammation, or bleeding of the gums," said lead study author Eva Muñoz Aguilera, D.D.S., M.Clin.Dent., senior researcher at UCL Eastman Dental Institute in London, United Kingdom. "Elevated blood pressure is usually asymptomatic, and many individuals may be unaware that they are at increased risk of cardiovascular complications. We aimed to investigate the association between severe periodontitis and high blood pressure in healthy adults without a confirmed diagnosis of hypertension."

The study included 250 adults with generalized, severe periodontitis (≥50% of teeth measured with gum infection) and a control group of 250 adults who did not have severe gum disease, all of whom were otherwise healthy and had no other chronic health conditions. The median age of the participants was 35 years, and 52.6% were female. The research was completed in collaboration with the department of dentistry at the Universitat Internacional de Catalunya in Barcelona, Spain.

All participants underwent comprehensive periodontal examinations including detailed measures of gum disease severity, such as full-mouth dental plaque, bleeding of the gums and the depth of the infected gum pockets. Blood pressure assessments were measured three times for each participant to ensure accuracy. Fasting blood samples were also collected and analyzed for high levels of white blood cells and high sensitivity C-reactive protein (hsCRP), as both are markers of increased inflammation in the body. Additional information analyzed as confounders included family history of cardiovascular disease, age, body mass index, gender, ethnicity, smoking and physical activity levels.

The researchers found that a diagnosis of gum disease was associated with higher odds of hypertension, independent of common cardiovascular risk factors. Individuals with gum disease were twice as likely to have high systolic blood pressure values ?140 mm Hg, compared to people with healthy gums (14% and 7%, respectively). Researchers also found:

The presence of active gum inflammation (identified by bleeding gums) was associated with higher systolic blood pressure.

Participants with periodontitis exhibited increased glucose, LDL ("bad" cholesterol), hsCRP and white blood cell levels, and lower HDL ("good" cholesterol) levels compared to those in the control group.

Nearly 50% of participants with gum disease and 42% of the control group had blood pressure values for a diagnosis of hypertension, defined as ?130/80 mmHg.

"This evidence indicates that periodontal bacteria cause damage to the gums and also triggers inflammatory responses that can impact the development of systemic diseases including hypertension," said corresponding author Francesco D'Aiuto, D.M.D., M.Clin.Dent., Ph.D., professor of periodontology and head of the periodontology unit at the UCL Eastman Dental Institute. "This would mean that the link between gum disease and elevated blood pressure occurs well before a patient develops high blood pressure. Our study also confirms that a worryingly high number of individuals are unaware of a possible diagnosis of hypertension."

D'Aiuto added, "Integration of hypertension screening by dental professionals with referrals to primary care professionals and periodontal disease screening by medical professionals with referrals to periodontists could improve detection and treatment of both conditions to improve oral health and reduce the burden of hypertension and its complications. Oral health strategies such as brushing teeth twice daily are proven to be very effective in managing and preventing the most common oral conditions, and our study's results indicate they can also be a powerful and affordable tool to help prevent hypertension."

This study did not account for other factors that may also impact blood pressure, such as abdominal obesity, salt intake, use of anti-inflammatory medications, hormone treatments or stress, or any other oral health conditions.

Dental procedures during pandemic are no riskier than a drink of water, study finds

A new study's findings dispel the misconception that patients and providers are at high risk of catching COVID-19 at the dentist's office.

SARS-CoV-2 spreads mainly through respiratory droplets, and dental procedures are known to produce an abundance of aerosols -- leading to fears that flying saliva during a cleaning or a restorative procedure could make the dentist's chair a high-transmission location.

Ohio State University researchers set out to determine whether saliva is the main source of the spray, collecting samples from personnel, equipment and other surfaces reached by aerosols during a range of dental procedures.

By analyzing the genetic makeup of the organisms detected in those samples, the researchers determined that watery solution from irrigation tools, not saliva, was the main source of any bacteria or viruses present in the spatter and spurts from patients' mouths.

Even when low levels of the SARS-CoV-2 virus were detected in the saliva of asymptomatic patients, the aerosols generated during their procedures showed no signs of the coronavirus. In essence, from a microbial standpoint, the contents of the spray mirrored what was in the office environment.

"Getting your teeth cleaned does not increase your risk for COVID-19 infection any more than drinking a glass of water from the dentist's office does," said lead author Purnima Kumar, professor of periodontology at Ohio State.

"These findings should help us open up our practices, make ourselves feel safe about our environment and, for patients, get their oral and dental problems treated -- there is so much evidence emerging that if you have poor oral health, you are more susceptible to COVID," Kumar said.

The study was published Wednesday, May 12, in the Journal of Dental Research.

Previous research has shown that dental-procedure aerosols tend to land on providers' faces and the patient's chest, and can travel as far as 11 feet. But the studies, catching the spray in petri dishes placed on people, equipment and around the room, found only that bacteria existed -- they rarely identified the organisms and never determined where they came from. Saliva has been the presumptive source for a long time.

When saliva was considered potentially deadly at the start of the pandemic, Kumar decided a long-term answer was needed to settle the question of whether saliva is the source of dental aerosols.

For the study, the team enrolled 28 patients receiving dental implants and restorations using high-speed drills or ultrasonic scaling procedures in Ohio State's College of Dentistry between May 4 and July 10, 2020. Researchers collected samples of saliva and irrigant (the water-based cleaning solutions used to flush out the mouth) before each procedure and, 30 minutes after the procedure, aerosol remnants -- condensate -- from providers' face shields, the patient's bib and an area 6 feet away from the chair.

Kumar and colleagues then put genome sequencing technology to use that wasn't available in the petri-dish days. This allowed them to first characterize the microbial mix in pre-procedure saliva and irrigants, which they could then compare to organisms in the aerosol samples collected later.

With the analytical method they used, the researchers did not need to characterize the microbes -- they instead looked for variations in sequences that provided enough information to identify the family of bacteria or viruses to which they belonged.

"Some species that live in your mouth can closely resemble those in water and the environment. Using this method, we don't even have to know the names of these organisms -- you can tell whether they are exactly genetically identical or genetically different," Kumar said. "If you use this granular approach to see these very nuanced differences in the genetic code, you can very accurately identify where they're coming from."

No matter the procedure or where the condensate had landed, microbes from irrigants contributed to about 78% of the organisms in aerosols while saliva, if present, accounted for 0.1% to 1.2% of the microbes distributed around the room.

Salivary bacteria were detected in condensate from only eight cases and of those, five patients had not used a pre-procedural mouth rinse. The SARS-CoV-2 virus was identified in the saliva of 19 patients, but was undetectable in aerosols in any of the cases.

The findings are reassuring, but also make sense, Kumar said: Irrigant dilutes saliva -- a "thick, viscous" substance -- by an estimated 20- to 200-fold, and the research is validated by a 2020 study that reported a less than 1% COVID-19 positivity rate among dentists.

Kumar noted that dentistry has long been at the forefront of infection-control practices in health care. During the pandemic, new protocols have included strengthened ventilation systems, extra aerosol suction equipment, N95 masks and face shields on top of goggles, and extended downtime between patients. She is hopeful this study's findings will make practitioners and patients feel at ease about being in the dentist's office -- with continued stringent protection in place.

"Dental surgeons and hygienists are always at the forefront of the war against bacteria in the mouth, and they of course did not feel safe because they are front-line workers surrounded by aerosol," said Kumar, who has a periodontology practice of her own and was one of the procedure operators in the study.

"Hopefully this will set their mind at rest because when you do procedures, it is the water from the ultrasonic equipment that's causing bacteria to be there. It's not saliva. So the risk of spreading infection is not high," she said. "However, we should not lose sight of the fact that this virus spreads through aerosol, and speaking, coughing or sneezing in the dental office can still carry a high risk of disease transmission."

Co-authors of the study include Archana Meethil, Shwetha Saraswat and Shareef Dabdoub of Ohio State and Prem Prashant Chaudhary of the National Institute of Allergy and Infectious Diseases.

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Good dental health may help prevent heart infection from mouth bacteria

Maintenance of good oral health is more important than use of antibiotics in dental procedures for some heart patients to prevent a heart infection caused by bacteria around the teeth, according to a new American Heart Association (AHA) scientific statement published today in the association's flagship journal, Circulation.

Infective endocarditis (IE), also called bacterial endocarditis, is a heart infection caused by bacteria that enter the bloodstream and settle in the heart lining, a heart valve or a blood vessel. It is uncommon, but people with heart valve disease or previous valve surgery, congenital heart disease or recurrent infective endocarditis have a greater risk of complications if they develop IE. Intravenous drug use also increases risk for IE. Viridans group streptococcal infective endocarditis (VGS IE) is caused by bacteria that collect in plaque on the tooth surface and cause inflammation and swelling of the gums. There's been concern that certain dental procedures may increase the risk of developing VGS IE in vulnerable patients.

The new guidance affirms previous recommendations that only four categories of heart patients should be prescribed antibiotics prior to certain dental procedures to prevent VGS IE due to their higher risk for complications from the infection:

those with prosthetic heart valves or prosthetic material used for valve repair;

those who have had a previous case of infective endocarditis;

adults and children with congenital heart disease; or

people who have undergone a heart transplant.

"Scientific data since the 2007 AHA guidelines support the view that limited use of preventive antibiotics for dental procedures hasn't increased cases of endocarditis and is an important step at combating antibiotic overuse in the population," said Walter R. Wilson, M.D., chair of the statement writing group and a consultant for the Division of Infectious Diseases, Department of Internal Medicine at Mayo Clinic in Rochester, Minn.

It has been over a decade since recommendations for preventing infective endocarditis were updated amid concerns of antibiotic resistance due to overprescribing. The American Heart Association's 2007 guidelines, which presented the biggest shift in recommendations from the Association on the prevention of infective endocarditis in more than 50 years, more tightly defined which patients should receive preventive antibiotics before certain dental procedures to the four high-risk categories. This change resulted in about 90% fewer patients requiring antibiotics.

The scientific statement writing group reviewed data on VGS IE since the 2007 guidelines to determine if the guidelines had been accepted and followed, whether cases of and mortality due to VGS IE have increased or decreased, and if the guidance might need to be adjusted.

The writing committee reports their extensive review of related research found:

There was good general awareness of the changes in the 2007 guidelines, however, adherence to the guidelines was variable. There was about a 20% overall reduction in prescribing preventive antibiotics among high-risk patients, a 64% decrease among moderate-risk patients, and a 52% decrease in those patients at low- or unknown-risk.

In a survey of 5,500 dentists in the U.S., 70% reported prescribing preventive antibiotics to patients even though the guidelines no longer recommend it, and this was most often for patients with mitral valve prolapse and five other cardiac conditions. The dentists reported that about 60% of the time the antibiotic regimen was recommended by the patient's physician, and 1/3 of the time was according to patient preference.

Since the stricter 2007 antibiotic guidelines, there is no convincing evidence of an increase in cases of VGS IE or increased mortality due to VGS IE.

The writing group supports the 2007 recommendation that only the highest risk groups of patients receive antibiotics prior to certain dental procedures to help prevent VGS IE.

In the presence of poor oral hygiene and gingival disease, VGS IE is far more likely to develop from bacteria attributable to routine daily activities such as toothbrushing than from a dental procedure.

Maintenance of good oral hygiene and regular access to dental care are considered as important in preventing VGS IE as taking antibiotics before certain dental procedures.

It is important to connect patients with services to facilitate access to dental care and assistance with insurance for dental coverage, especially in those patients at high risk for VGS IE.

It is still appropriate to follow the recommendation to use preventive antibiotics with high-risk patients undergoing dental procedures that involve manipulation of the gum tissue or infected areas of the teeth, or perforation of the membrane lining the mouth.

The scientific statement was prepared by the volunteer writing committee on behalf of the American Heart Association's Young Hearts Rheumatic Fever, Endocarditis and Kawasaki Disease Committee; the Council on Lifelong Congenital Heart Disease and Heart Health in the Young; the Council on Cardiovascular and Stroke Nursing; and the Council on Quality of Care and Outcomes Research.

How Teeth Sense the Cold

For people with tooth decay, drinking a cold beverage can be agony.

"It's a unique kind of pain," says David Clapham, vice president and chief scientific officer of the Howard Hughes Medical Institute (HHMI). "It's just excruciating."

Now, he and an international team of scientists have figured out how teeth sense the cold and pinpointed the molecular and cellular players involved. In both mice and humans, tooth cells called odontoblasts contain cold-sensitive proteins that detect temperature drops, the team reports March 26, 2021, in the journal Science Advances. Signals from these cells can ultimately trigger a jolt of pain to the brain.

The work offers an explanation for how one age-old home remedy eases toothaches. The main ingredient in clove oil, which has been used for centuries in dentistry, contains a chemical that blocks the "cold sensor"protein, says electrophysiologist Katharina Zimmermann, who led the work at Friedrich-Alexander University Erlangen-Nürnberg in Germany.

Developing drugs that target this sensor even more specifically could potentially eliminate tooth sensitivity to cold, Zimmermann says. "Once you have a molecule to target, there is a possibility of treatment."

Mystery channel

Teeth decay when films of bacteria and acid eat away at the enamel, the hard, whitish covering of teeth. As enamel erodes, pits called cavities form. Roughly 2.4 billion people -- about a third of the world's population -- have untreated cavities in permanent teeth, which can cause intense pain, including extreme cold sensitivity.

No one really knew how teeth sensed the cold, though scientists had proposed one main theory. Tiny canals inside the teeth contain fluid that moves when the temperature changes. Somehow, nerves can sense the direction of this movement, which signals whether a tooth is hot or cold, some researchers have suggested.

"We can't rule this theory out," but there wasn't any direct evidence for it, says Clapham a neurobiologist at HHMI's Janelia Research Campus. Fluid movement in teeth -- and tooth biology in general -- is difficult to study. Scientists have to cut through the enamel -- the hardest substance in the human body -- and another tough layer called dentin, all without pulverizing the tooth's soft pulp and the blood vessels and nerves within it. Sometimes, the whole tooth "will just fall to pieces," Zimmermann says.

Zimmerman, Clapham, and their colleagues didn't set out to study teeth. Their work focused primarily on ion channels, pores in cells' membranes that act like molecular gates. After detecting a signal -- a chemical message or temperature change, for example -- the channels either clamp shut or open wide and let ions flood into the cell. This creates an electrical pulse that zips from cell to cell. It's a rapid way to send information, and crucial in the brain, heart, and other tissues.

About fifteen years ago, when Zimmermann was a postdoc in Clapham's lab, the team discovered that an ion channel called TRPC5 was highly sensitive to the cold. But the team didn't know where in the body TRPC5's cold-sensing ability came into play. It wasn't the skin, they found. Mice that lacked the ion channel could still sense the cold, the team reported in 2011 in the journal Proceedings of the National Academy of Sciences.

After that, "we hit a dead end," Zimmermann says. The team was sitting at lunch one day discussing the problem when the idea finally hit. "David said, 'Well, what other tissues in the body sense the cold?' Zimmermann recalls. The answer was teeth.

The whole tooth

TRPC5 does reside in teeth -- and more so in teeth with cavities, study coauthor Jochen Lennerz, a pathologist from Massachusetts General Hospital, discovered after examining specimens from human adults.

A novel experimental set up in mice convinced the researchers that TRPC5 indeed functions as a cold sensor. Instead of cracking a tooth open and solely examining its cells in a dish, Zimmermann's team looked at the whole system: jawbone, teeth, and tooth nerves. The team recorded neural activity as an ice-cold solution touched the tooth. In normal mice, this frigid dip sparked nerve activity, indicating the tooth was sensing the cold. Not so in mice lacking TRPC5 or in teeth treated with a chemical that blocked the ion channel. That was a key clue that the ion channel could detect cold, Zimmermann says. One other ion channel the team studied, TRPA1, also seemed to play a role.

The team traced TRPC5's location to a specific cell type, the odontoblast, that resides between the pulp and the dentin. When someone with a a dentin-exposed tooth bites down on a popsicle, for example, those TRPC5-packed cells pick up on the cold sensation and an "ow!" signal speeds to the brain.

That sharp sensation hasn't been as extensively studied as other areas of science, Clapham says. Tooth pain may not be considered a trendy subject, he says, "but it is important and it affects a lot of people."

Zimmermann points out that the team's journey towards this discovery spanned more than a decade. Figuring out the function of particular molecules and cells is difficult, she says. "And good research can take a long time."