Saturday, October 7, 2017

Dentists can harvest stem cells



  • Dr. Karl Kingsley and Dr. James Mah, research professors with the UNLV School of Dental Medicine.
  • Credit: Josh Hawkins/UNLV Creative Services

Stem cells. Few research discoveries hold as much promise of single-handedly expanding medical treatment options as they do. Miraculously able to act as transformers—either re-creating or morphing into a variety of cell types found within the organisms they originate from—stem cells offer humanity hope for new, more effective therapies against a number of chronic and terminal diseases. And finding them is surprisingly easy.
“Stem cells can be extracted from nearly any living tissue,” said Dr. James Mah, director of UNLV’s advanced education program in orthodontics, doctor of dental surgery, and dental researcher. “In fact, stem cells can even be found in tissues of the deceased.”
But in spite of all their potential, there’s a catch: “The biggest challenges with stem cells are gathering enough of them to work with and keeping them viable until they are needed,” Dr. Mah said.
He and UNLV biomedical sciences professor Karl Kingsley—along with a handful of undergraduate, graduate, and postdoctoral dental students—decided to take on this challenge, cutting their teeth in stem cell research by exploring those pearly whites in new ways. In the process, they developed a new method for extracting large numbers of stem cells they could then preserve from a surprisingly abundant source: wisdom teeth.
“More and more adults—approximately 5 million throughout the country—have their wisdom teeth, or third molars, removed,” Kingsley said. “Extracting teeth is relatively common among patients undergoing orthodontic treatments. And the majority of those teeth are healthy, containing viable tooth root pulp that offers opportunities for reproducing cells that have been damaged or destroyed by injuries or disease.”

A tough nut to crack

Tooth root pulp is home to two types of prized stem cells. The first, pluripotent stem cells, have the ability to become any cell in the organism from which they’re drawn. The second, multipotent stem cells, transform into specific types of cells within that organism.
Knowing where to find these cells was one thing. Recovering them, the researchers knew, would be another.
Common methods for extracting root pulp involve drilling into, removing the top of, or shattering the tooth. Each method has its detriments, Dr. Mah said, all of which lead to a low stem-cell recovery rate: damaging heat from drilling, corrosive elements in the water teeth are rinsed in, contaminating enamel particulates, and more. So the researchers sought to discover how to extract pulp in a manner that consistently produced a higher yield.
“Initially, the answer seemed simple: crack the tooth in half like a nut and remove the pulp,” Dr. Mah said.
Unfortunately, teeth have irregular surfaces and non-uniform shapes, so cracking teeth usually produces the same shattering effect as a hammer, thereby reducing the number of viable stem cells.
Happy Ghag, then a dental student working with Dr. Mah and Kingsley on the project, thought he might have solution to the dilemma. He approached Mohamed Trabia (UNLV Howard R. Hughes College of Engineering’s associate dean for research, graduate studies, and computing) and Brendan O’Toole (Mendenhall Innovation Program director and mechanical engineering researcher) to discuss fracture analysis.
“Happy had reviewed fracture mechanics literature and decided on a technique that scored the tooth to enable a clean break, similar to the process for custom-cut glass,” O’Toole said. After a few discussions, some of Engineering’s personnel helped Ghag fabricate the device.
The completed instrument, which the research team facetiously dubbed the “Tooth Cracker 5000,” uses a clamp to hold a tooth in position for a cutting tool to score the surface and a blade to crack it. The result: a perfectly halved tooth, with immediate access to undamaged and uncontaminated root pulp.
For O’Toole, this was just another successful collaboration between the two units, as Mechanical Engineering had been interacting with the School of Dental Medicine’s orthodontic program for a few years.
“Orthodontics, by definition, is a bioengineering topic,” O’Toole said. “They design and place mechanisms in people’s mouths that help move teeth into optimum position. The interaction between our departments makes a lot of sense.”
With the Tooth Cracker 5000 complete, Dr. Mah and Kingsley tested the fracture rate of 25 teeth, achieving a 100 percent rate of success. The fracture idea and design prototype had worked perfectly.

Excavating for success

Now that the researchers had cracked the challenge of accessing the root pulp, it was on to determining how many viable stem cells they could recover from the fractured teeth. Average pulp recovery rates employing common extraction methods (i.e., shattering, drilling, etc.) come in at around 20 percent, Dr. Mah noted.
It was time to test the mettle of their new fracture method. Dr. Mah and Kingsley dyed 31 fractured teeth pulp samples to highlight any viable stem cells the teeth contained. Dead cells would turn blue when exposed to the dye. Living cells would appear clear.
They looked under the microscope. Eighty percent of their extracted cells remained clear after the dye was introduced.
“Saying the test results were promising is a gross understatement,” Dr. Mah said. “We realized we’d invented an extraction process that produced four times the recovery success rate for viable stem cells. The potential application is enormous.”

Replicating for a rainy day

After mastering fracturing and extraction, it was time for the team to determine what kind of stem cells could be harvested and how best to store them.
Normal cells within the body typically die after 10 replications or passages, whereas stem cells can replicate indefinitely, Kingsley indicated. To isolate the stem cells from the rest of the root pulp, the researchers harvested cells from the pulp and cultured them on a petri dish. Once the cells covered the dish, they split the culture in half and repeated the process between 10 and 20 times.
By the end of the culturing, all nonstem cells had expired. Kingsley captured the remaining stem cells and collected their ribonucleic acid (RNA), which is converted into proteins that become biomarkers his team could use to characterize each stem cell type and its respective rate of replication.
“Scientists around the world are trying to figure out what type of stem cells can be coaxed into becoming new cells or different tissue types,” Kingsley said. “We already know some populations of dental pulp stem cells can be converted into neurons, which could become therapies for cognitive diseases such as Alzheimer’s or Parkinson’s.”
Kingsley noted that teams of scientists around the world are working with animal models to test using stem cells to treat neurological conditions. Early indications, he said, are positive. Although there is still a need for additional tests, Kingsley indicated that the next logical step in this research would be to test stem cells in humans to treat any number of chronic illnesses people face.
“There are potential applications of stem cells for multiple diseases, including cancer, arthritis, and lung disease,” Kingsley said. “The next challenge is reliably collecting the stem cells early enough and storing them successfully so they can be used when needed.”

Preserving the prize

According to multiple studies, the number of pluripotent stem cells found in teeth decrease dramatically after adults reach the age of 30, Kingsley said. However, people could donate stem cells found in their teeth much like they may donate their blood prior to a surgical procedure or preserve their umbilical cords. If people elected to have their wisdom teeth removed or were having a root canal performed, their stem cells could be harvested at that time and stored for future use.
Creating that possibility has led Dr. Mah and Kingsley to the next step in their research: the cryogenic process.
“There is no standard cryogenesis, or freezing process, for storing stem cells,” Kingsley said. “There are multiple organizations that collect and freeze teeth for future studies and use, but there is no evidence about the long-term effects of cryopreservation. We can’t answer yet just how long the cells will survive.”
In 2011 dental student Allison Tomlin studied different populations of stem cells and their viability after being thawed. Every year since, Kingsley and his team have thawed a portion of Tomlin’s sample and evaluated the viability of remaining stem cells. Initial findings—which Kingsley, Tomlin, and R. Michael Sanders (clinical sciences professor in the dental school) published in their Biomaterials and Biomechanics in Bioengineering article “The Effects of Cryopreservation on Human Dental Pulp-derived Mesenchymal Stem Cells”—indicate that rapidly dividing cells have higher rates of viability year after year compared to slower dividing cells. If these results remain constant, the stem cells could be sorted before the freezing process based on when they might be needed.
“The work Dr. Kingsley and I are doing is part of a paradigm shift,” Dr. Mah said. “Our fracturing process could hasten the collection and cryogenesis process, thereby preserving a high stem-cell count that furthers research into how using these cells can aid healing and potentially cure diseases.”

Friday, October 6, 2017

Antibiotics for dental procedures linked to superbug infection, study shows

                    

Antibiotics prescribed by dentists may contribute to the growing problem of Clostridium difficile (C. diff), a serious and potentially deadly infection that causes severe diarrhea, suggests research presented at IDWeek 2017. And many of those antibiotics are likely unnecessary, researchers note.

Taking antibiotics can put patients at risk for developing C. diff and illustrates the importance of using the medications only when needed. The Minnesota Department of Health (MDH) tracked community-associated C. diff infections - meaning those in patients who did not have an overnight stay in a hospital or nursing home - in five counties in the state. During the six-year period, researchers determined 15 percent of those with the infection who had taken antibiotics had them prescribed for dental procedures.

But one-third of those patients' medical charts included no mention of receiving dental procedure-related antibiotics, researchers determined. An earlier survey conducted by the MDH found 36 percent of dentists prescribed antibiotics in situations that are generally not recommended by the American Dental Association (ADA) and reported challenges to making appropriate antibiotic prescribing decisions, including confusion about or perceived conflicts among prescribing guidelines.

"Dentists have been overlooked as a source of antibiotic prescribing, which can potentially delay treatment when doctors are trying to determine what is causing a patient's illness," said Stacy Holzbauer, DVM, MPH, lead author of the study and career epidemiology field officer for the CDC and MDH. "It's important to educate dentists about the potential complications of antibiotic prescribing, including C. diff. Dentists write more than 24.5 million prescriptions for antibiotics a year. It is essential that they be included in efforts to improve antibiotic prescribing."

Dentists appropriately prescribe antibiotics in certain situations, such as to treat infections stemming from a tooth abscess. However, some dentists prescribe antibiotics prophylactically before a dental procedure to prevent a heart infection in patients with heart conditions, or to prevent an infection of an artificial joint, such as a hip or knee replacement. The ADA no longer recommends preventive antibiotics in most of those cases, as it once did.

"It is possible some dentists aren't aware of the updated recommendations or are being asked by other healthcare providers to continue preventive antibiotics despite the change," said Dr. Holzbauer. Current recommendations note the risk of taking antibiotics - such as developing C. diff - is greater than the risk of an infection in those cases. Further, the inappropriate use of antibiotics helps fuel the creation of drug-resistant bacteria, which are very difficult to treat and are an increasing public health threat.

In the study, MDH researchers interviewed 1,626 people with community-associated C. diff between 2009 and 2015. Of those, 926 (57 percent) reported they had been prescribed antibiotics, 136 (15 percent) of those for dental procedures. The study found patients who were prescribed antibiotics for dental procedures tended to be older and more likely to receive clindamycin, an antibiotic that is associated with C. diff infection. Of those who had received antibiotics for a dental procedure, 34 percent had no mention of antibiotics in their medical charts, illustrating the disconnect between dental and medical care. During routine medical appointments, patients should bring up dental visits and medications, including antibiotics - they have taken. In addition, healthcare providers should ask patients about dental visits and medications taken for dental reasons.

Antibiotics kill bad and good bacteria in the gastrointestinal (GI) system. Wiping out the protective bacteria can allow the growth of C. diff bacteria, leading to severe and potentially deadly diarrhea. C. diff can occur after just one dose of antibiotics and is one of the top three most urgent antibiotic-resistant threats identified by the CDC. It caused almost half a million infections and led to 15,000 deaths in a single year, according to CDC estimates.

"Research has shown that reducing outpatient antibiotic prescribing by 10 percent could decrease C. diff rates outside of hospitals by 17 percent," said Dr. Holzbauer. "Limiting the use of inappropriate antibiotics in dentistry could also have a profound impact."

While the ADA has expressed a commitment to and is an active partner in antibiotic stewardship, a 2015 MDH survey of dentists found fewer than half were concerned about adverse drug effects, antibiotic resistance or C. diff as factors that influenced their prescribing decisions. That's likely because they are unaware when their patients develop C. diff, Dr. Holzbauer said. Better communication between dental and medical communities and improved history taking by all prescribers would help, she said.


Monday, September 25, 2017

Chronic migraine cases are amplified by jawbone disorder

                     


In a study, researchers at the University of São Paulo's Ribeirão Preto School of Medicine (FMRP-USP), in Brazil, finds that the more frequent the migraine attacks, the more severe will be the so-called temporomandibular disorder, or TMD. The temporomandibular joint acts like a sliding hinge connecting the jawbone to the skull, therefore the disorder's symptoms includes difficulty chewing and joint tension.
"Our study shows that patients with chronic migraine, meaning attacks occurring on more than 15 days per month, are three times as likely to report more severe symptoms of TMD than patients with episodic migraine," said Lidiane Florencio, the first author of the study, which is part of the Thematic Project "Association study of clinical, functional and neuroimaging in women with migraine", supported by the São Paulo Research Foundation - FAPESP.
Previous studies already indicated that migraine is somehow associated with pain in the chewing muscles. However, this research was the first to consider the frequency of migraine attacks when analyzing its connection with TMD: eighty-four women in their early to mid-thirties were assessed, being that 21 were chronic migraine patients, 32 had episodic migraine, while 32 with no history of migraine were included as controls - the results were published in the Journal of Manipulative and Physiological Therapeutics.
Signs and symptoms of TMD were observed in 54% of the control participants without migraine, 80% of participants with episodic migraine, and 100% of those with chronic migraine.
For Florencio, central sensitization may explain the association between the frequency of migraine attacks and the severity of TMD.
"The repetition of migraine attacks may increase sensitivity to pain," she said. "Our hypothesis is that migraine acts as a factor that predisposes patients to TMD. On the other hand, TMD can be considered a potential perpetuating factor for migraine because it acts as a constant nociceptive input that contributes to maintaining central sensitization and abnormal pain processes." Nociceptive pain is caused by a painful stimulus on special nerve endings called nociceptors.
Migraine and TMD have very similar pathological mechanisms. Migraine affects 15% of the general population, and progression to the chronic form is expected in about 2.5% of migraine sufferers. On the other hand TMD is stress-related as much as it has to do with muscle overload. Patients display joint symptoms - such as joint pain, reduced jaw movement, clicking or popping of the temporomandibular joint - but also develop a muscular condition, including muscle pain and fatigue, and/or radiating face and neck pain.
Which came first?
TMD and migraine are comorbidities. However, while people who suffer from migraine are predisposed to have TMD, people with TMD will not necessarily have migraine.
"Migraine patients are more likely to have signs and symptoms of TMD, but the reverse is not true. There are cases of patients with severe TMD who don't present with migraine," said Débora Grossi, the lead researcher for the study and principal investigator for the Thematic Project.
The researchers believe that TMD may increase the frequency and severity of migraine attacks, even though it does not directly cause migraine.
"We do know migraine isn't caused by TMD," Florencio said. "Migraine is a neurological disease with multifactorial causes, whereas TMD, like cervicalgia - neck pain - and other musculoskeletal disorders, is a series of factors that intensify the sensitivity of migraine sufferers. Having TMD may worsen one's migraine attacks in terms of both severity and frequency."
The journal article concludes that an examination of TMD signs and symptoms should be clinically conducted in patients with migraine.
"Our findings show the association with TMD exists but is less frequent in patients with rare or episodic migraine," Grossi said. "This information alone should change the way clinicians examine patients with migraine. If migraine sufferers tend to have more severe TMD, then health professionals should assess such patients specifically in terms of possible signs and symptoms of TMD."

Thursday, September 14, 2017

Don't blame your genes for your toothache, twin study shows

                     


For the first time, investigators have looked at the role that genes and the oral microbiome play in the formation of cavities and have found that your mother was right: The condition of your teeth depends on your dietary and oral hygiene habits. The study appears September 13 in Cell Host & Microbe.

"Limiting sugar consumption and acid buildup in the mouth have been part of the dogma of the dental community for some time," says senior author Karen Nelson, President of the J. Craig Venter Institute (JCVI). "This work introduces specific taxa of bacteria that can be acquired through the environment and that have the ability to induce cavities."

Since the early 20th century, dentists and other experts have known that Streptococcus bacteria in the mouth are linked to the formation of cavities. Now, with the ability to study studying the microbiome, the investigators were able to take a closer look at specific taxa that are important.

To separate the role of heritability versus the environment, Nelson and her team turned to a popular method for studying such interactions: identical and fraternal twins. Specifically, they profiled the oral microbiomes of 485 twin pairs between the ages of 5 and 11. There were 280 fraternal twins and 205 identical twins--and one set of triplets. The samples were obtained with mouth swabs.

"We decided to focus on children because we hypothesized twow things--that the oral microbiome rapidly changes with age, and also that child twin pairs are likely to have a shared environment," Nelson says. "This allowed us to better control the influence of shared and unique environments."

Their results--driven with significant analysis input from co-authors Josh Espinoza (JCVI Engineer) and Chris Dupont (JCVI Associate Professor)--showed that identical twins had oral microbiomes that were more similar to each other than those of fraternal twins, indicating that there is genetic contribution to which kinds of bacteria are likely to be present in the mouth. However, the taxa that were linked most closely to heritability were not the ones that play a role in cavity formation. In addition, they found that the heritable strains of bacteria decrease in abundance as people get older, whereas the ones linked to the environment increase.

An important additional finding was the link between certain bacterial species and sugar consumption. Bacteria that were associated with fewer cavities were in lower abundance in twins who had a lot of added sugar in their food and drinks. In contrast, bacteria that are more common in children who consume a lot of sugar were associated with having more cavities.

The team plans to continue studying the twins over repeat visits to examine changing patterns in the oral microbiome. They are also looking at functional differences in the oral microbiomes of identical and fraternal twin pairs that have various states of oral health.
  

Friday, September 8, 2017

Many middle-aged adults report dental pain, embarrassment and poor prevention


The dental health of middle-aged Americans faces a lot of problems right now, and an uncertain future to come, according to new results from the University of Michigan National Poll on Healthy Aging.

One in three Americans between the ages of 50 and 64 say they're embarrassed by the condition of their teeth. A slightly larger percentage say dental problems have caused pain, difficulty with eating, missed work or other health problems in the past two years. Forty percent of those polled don't get regular cleanings or other preventive care that can help prevent dental problems.

Insurance coverage appears to have a lot to do with this lack of care. Overall, 28 percent of respondents said they don't have dental coverage. But that percentage was much higher -- 56 percent -- among those who say they only seek care for serious dental problems.

As for the future, 51 percent of those surveyed said they simply didn't know how they will get dental insurance coverage after they turn 65.

Another 13 percent of middle-aged adults expect to count on Medicare or Medicaid to cover their oral care needs after that age. Traditional Medicare does not cover routine dental care, and Medicaid dental coverage is often limited.

The poll, based on a nationally representative sample of older adults, was conducted by the U-M Institute for Healthcare Policy and Innovation with support from AARP and Michigan Medicine, U-M's academic medical center.

"Our findings highlight a stark divide among middle-aged Americans in terms of their oral health now, and a real uncertainty about how they will get and pay for care as they age," says associate poll director Erica Solway, Ph.D. "This is not out of disregard for the importance of preventive dental care - more than three-quarters of the people we polled agree that regular care is important to preventing problems later. But it does highlight opportunities to improve access to care and insurance options after age 65."

Solway and poll director Preeti Malani, M.D., a professor of internal medicine at the U-M Medical School, divided the poll respondents into three groups based on their responses about their use of dental care:
  • prevention-focused: about 60 percent of the sample, who got regular preventive care as well as getting attention for dental problems
  • inconsistent prevention: the 17 percent who sought preventive dental care occasionally
  • problem-only: the 23 percent who went to the dentist only for serious dental problems.
"We know that oral health is a critical factor in overall wellness, and this research helps us identify some key issues - such as affordability and coverage - that we can focus on to address those 40% who are not prevention-focused," stated Dr. Alison Bryant, Senior Vice President of Research for AARP.

A clear divide
Poll respondents who were female, white, had higher incomes or had insurance were much more likely than others to take a prevention-focused approach to dental care. Men, African Americans, Hispanics, those with lower income, or those without insurance were more likely to seek dental care for problems only.

The differences among the three groups was also apparent when the U-M team asked about how easy it was to get care, and why they might not have sought care.

Among those who were prevention-focused, only 13 percent said they had delayed or hadn't received dental care when they needed it in the last two years. But that jumped to 35 percent in the inconsistent-prevention group, and 56 percent in the problem-only group.

Why didn't poll respondents get needed dental care? Cost was the most commonly reported answer, given by 69 percent who said they did not get or delayed needed care. Respondents also reported they were afraid of the dentist, couldn't find time to go, or couldn't find a dentist. Of the people who didn't receive care they needed, one in five cited fear of the dentist as a major factor.

Uncertain future
Looking ahead to the years beyond their 65th birthday - an age when most Americans become eligible for Medicare- the poll respondents were uncertain about how they'd get dental insurance.
Some - 16 percent - said they counted on employer-based coverage or a retirement-based plan. Another 12 percent said they planned to buy supplemental dental insurance.

And in addition to the half of respondents who indicated that they didn't know whether they will have dental insurance at all after age 65, another eight percent said they'd just go without it.

But it's the remaining respondents - the 13 percent who expect Medicare or Medicaid to cover their dental care in their older years - that concern the poll leaders the most.

"Traditional Medicare does not cover dental care, and many states offer very limited or no dental coverage for adults with Medicaid," says Malani. "Even those who were diligent about seeing the dentist and had dental insurance throughout adulthood may find it harder to afford dental care as they get older and coverage options may be more limited."

The nationally representative sample included 1,066 people ages 50 to 64, who answered a wide range of questions online; laptops and Internet access were provided to those who did not already have it.
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A full report of the findings and methodology is available at http://www.healthyagingpoll.org.

New dental imaging method uses squid ink to fish for gum disease



Squid ink might be a great ingredient to make black pasta, but it could also one day make getting checked for gum disease at the dentist less tedious and even painless. By combining squid ink with light and ultrasound, a team led by engineers at the University of California San Diego has developed a new dental imaging method to examine a patient's gums that is non-invasive, more comprehensive and more accurate than the state of the art.

"The last time I was at the dentist, I realized that the tools that are currently being used to image teeth and gums could use significant updating," said Jesse Jokerst, a nanoengineering professor at UC San Diego and senior author of the study.

The conventional method for dentists to assess gum health is to use an instrument called a periodontal probe -- a thin, hook-like metal tool that's marked like a tiny measuring stick and inserted in between the teeth and gums to see whether and how much the gums have shrunk back from the teeth, creating pockets. This method of measuring pocket depth is the gold standard used in dentistry. A pocket depth measuring one to two millimeters indicates healthy gums while three millimeters and deeper is a sign of gum disease. The deeper the pockets, the more severe the gum disease.

However, procedures using the periodontal probe are invasive, uncomfortable and sometimes painful for the patient. Measurements can also vary greatly between dentists, and the probe is only capable of measuring the pocket depth of one spot at a time.

In a paper published on Sept. 7 in the Journal of Dental Research, Jokerst and his team at UC San Diego introduced an innovative method that can image the entire pocket depth around the teeth consistently and accurately, without requiring any painful poking and prodding.

"Using the periodontal probe is like examining a dark room with just a flashlight and you can only see one area at a time. With our method, it's like flipping on all the light switches so you can see the entire room all at once," Jokerst said.

The method begins by rinsing the mouth with a paste made of commercially available food-grade squid ink mixed with water and cornstarch. The squid-ink-based rinse serves as a contrast agent for an imaging technique called photoacoustic ultrasound. This involves shining a light signal -- usually a short laser pulse -- onto a sample, which heats up and expands, generating an acoustic signal that researchers can analyze. "Light in, sound out," Jokerst said.

Squid ink naturally contains melanin nanoparticles, which absorb light. During the oral rinse, the melanin nanoparticles get trapped in the pockets between the teeth and gums. When researchers shine a laser light onto the area, the squid ink heats up and quickly swells, creating pressure differences in the gum pockets that can be detected using ultrasound. This method enables researchers to create a full map of the pocket depth around each tooth -- a significant improvement over the conventional method.

Researchers tested their photoacoustic imaging method in a pig model containing a mix of shallow and deep pockets in the gums. While their results closely matched measurements taken using a periodontal probe, they were also consistent across multiple tests. On the other hand, measurements with the periodontal probe varied significantly from one test to another.

"It's remarkable how reproducible this technique is compared to the gold standard," Jokerst said.
Moving forward, the team will be collaborating with dentists and testing their method in humans. Future work also includes minimizing the taste of the squid ink oral rinse -- it's salty and somewhat bitter -- and replacing laser lights with inexpensive, more portable light systems like LEDs. The team's ultimate goal is to create a mouthpiece that uses this technology to measure periodontal health.

Tuesday, August 22, 2017

A new dental restoration composite more durable than the conventional material



Fewer trips to the dentist may be in your future, and you have mussels to thank.

Inspired by the mechanisms mussels use to adhere to inhospitable surfaces, UC Santa Barbara researchers have developed a new type of dental composite that provides an extra layer of durability to treated teeth. The potential payoff? Longer lasting fillings, crowns, implants and other work.
"It's as hard as a typical dental restoration but less likely to crack," Kollbe Ahn, a materials scientist at UCSB's Marine Science Institute, said of the composite. The research is highlighted in the journal Advanced Materials. The paper, of which Ahn is the corresponding author, is the result of collaboration between research and industry.

On average, a dental restoration lasts five to 10 or so years before needing replacement. The time frame depends on the type of restoration and how well the patient cares for the treated tooth. However, the continual onslaught of chewing, acidic and hard foods, poor hygiene, nighttime tooth grinding, generally weak teeth and even inadequate dental work can contribute to a filling's early demise -- and another expensive and possibly less-than-pleasant experience in the dental chair.

According to Ahn, one of the primary reasons restorations fall out or crack is brittle failure of the bond with the surrounding tooth. "All dental composites have micro-particles to increase their rigidity and prevent their shrinkage during their curing process," he explained. "But there's a trade-off: When the composite gets harder, it gets more brittle."

With enough pressure or wear and tear, a crack forms, which then propagates throughout the entire restoration. Or, the gap between the tooth and the restoration results in restoration failures, including marginal tooth decay.

So Ahn and his colleagues looked to nature -- mussels, to be exact -- to find a way not only to maintain strength and hardness but also to add durability. Having perfected the art of adhering to irregular surfaces under the variable conditions of the intertidal zone -- evolving to resist pounding waves, the blazing heat of the sun and cycles of salt water immersion and windy dryness -- mussels presented the ideal model for more durable dental restoration materials. The byssal threads they use to affix to surfaces allow them to resist the forces that would tear them from their moorings.

"In nature, the soft collagenous core of the mussel's byssal threads is protected by a 5-to-10 micrometer thick, hard coating, which is also extensible and thus, tough," Ahn said. This durability and flexibility allow the mollusks to stick to wet mineral surfaces in harsh environments that involve repeated push-and-pull stress.

Key to this mechanism is what the scientists call dynamic or sacrificial bonding -- multiple reversible and weak bonds on the sub-nanoscopic molecular level that can dissipate energy without compromising the overall adhesion and mechanical properties of the load-bearing material.

"Say you have one strong bond," Ahn explained. "It may be strong but once it breaks, it breaks. If you have several weaker bonds, you would have to break them one by one." Breaking each weak bond, he continued, would dissipate energy, so the overall energy required to break the material would be greater than with a single strong bond.

This type of bonding occurs in many biological systems, including animal bone and tooth. The mussel's byssus contain a high number of unique chemical functional groups called catechols, which are used to prime and promote adhesion to wet mineral surfaces. The new study shows that using a catecholic coupling agent instead of the conventional silane coupling agent provides 10 times higher adhesion and a 50 percent increase in toughness compared to current dental restorative resin composites.

While research has proven this toughening mechanism in soft materials, this study is one of the first -- if not the first -- to prove it with rigid and load-bearing materials.

This proof-of-concept, which also demonstrates no cytotoxicity, could mean tougher, more durable dental fillings. And that, in the long run, could mean fewer dental visits. Because each replacement filling also requires the dentist to file the surrounding tooth to prime its surface, given enough replacements a tooth might need to be crowned or extracted; and if not replaced, the tooth loss could have adverse consequences for the individual's diet and health.

The next step, Ahn said, is to increase the material's durability even further.

"By changing the molecular design you could have even denser coupling agents that exist on the surface, and then we can have a stronger and more durable dental composite," he said, estimating a commercial product within a couple of years.