Monthly Archives: August 2019

How To Grow Tooth Enamel

Scientists say they have finally cracked the problem of repairing tooth enamel.

Though enamel is the hardest tissue in the body, it cannot self-repair. Now scientists have discovered a method by which its complex structure can be reproduced and the enamel essentially “grown” back.

The team behind the research say the materials are cheap and can be prepared on a large scale. “After intensive discussion with dentists, we believe that this new method can be widely used in future,” said Dr Zhaoming Liu, co-author of the research from Zhejiang University in China.

Tooth decay is extremely common: according to 2016 figures about 2.4 billion people worldwide live with caries in permanent teeth, while 486 million children have decay in their milk teeth. At present, materials such as resin, metal alloys, amalgam and ceramics are used to repair damaged tooth enamel but they are not ideal.

Electron microscope images of human tooth enamel that has been repaired for six, 12 and 48 hours. The blue area is the native enamel; the green is the repaired enamel

“The resin-based material still cannot adhere well on enamel, and they will get loose after around five years,” said Liu.

While scientists have been chipping away at the issue for years through a number of approaches, they have encountered problems – not least that it is difficult to reproduce the complex structure of natural tooth enamel.

The researchers behind the latest study, published in the journal Science Advances, say they got around this problem by developing a way to produce tiny clusters of calcium phosphate – the main component of enamel – with a diameter of just 1.5 nanometres – far smaller than those previously employed.


An army of microrobots can wipe out dental plaque

A sometimes unpleasant scraping with mechanical tools to remove plaque from teeth. What if, instead, a dentist could deploy a small army of tiny robots to precisely and non-invasively remove that buildup? A team of engineers, dentists, and biologists from the University of Pennsylvania developed a microscopic robotic cleaning crew. With two types of robotic systems—one designed to work on surfaces and the other to operate inside confined spaces—the scientists showed that robots with catalytic activity could ably destroy biofilms, sticky amalgamations of bacteria enmeshed in a protective scaffolding. Such robotic biofilm-removal systems could be valuable in a wide range of potential applications, from keeping water pipes and catheters clean to reducing the risk of tooth decay, endodontic infections, and implant contamination.

The work, published in Science Robotics, was led by Hyun (Michel) Kooof the School of Dental Medicine and Edward Steager of the School of Engineering and Applied Science.

With a precise, controlled movement, microrobots cleared a glass plate of a biofilm, as shown in this time-lapse image

This was a truly synergistic and multidisciplinary interaction,” says Koo. “We’re leveraging the expertise of microbiologists and clinician-scientists as well as engineers to design the best microbial eradication system possible. This is important to other biomedical fields facing drug-resistant biofilms as we approach a post-antibiotic era.

Treating biofilms that occur on teeth requires a great deal of manual labor, both on the part of the consumer and the professional,” adds Steager. “We hope to improve treatment options as well as reduce the difficulty of care.”

Biofilms can arise on biological surfaces, such as on a tooth or in a joint or on objects, like water pipes, implants, or catheters. Wherever biofilms form, they are notoriously difficult to remove, as the sticky matrix that holds the bacteria provides protection from antimicrobial agents.

In previous work, Koo and colleagues have made headway at breaking down the biofilm matrix with a variety of outside-the-box methods. One strategy has been to employ iron-oxide-containing nanoparticles that work catalytically, activating hydrogen peroxide to release free radicals that can kill bacteria and destroy biofilms in a targeted fashion.

Serendipitously, the Penn Dental Medicine team found that groups at Penn Engineering led by Steager, Vijay Kumar, and Kathleen Stebe were working with a robotic platform that used very similar iron-oxide nanoparticles as building blocks for microrobots. The engineers control the movement of these robots using a magnetic field, allowing a tether-free way to steer them.

Together, the cross-school team designed, optimized, and tested two types of robotic systems, which the group calls catalytic antimicrobial robots, or CARs, capable of degrading and removing biofilms. The first involves suspending  iron-oxide nanoparticles in a solution, which can then be directed by magnets to remove biofilms on a surface in a plow-like manner. The second platform entails embedding the nanoparticles into gel molds in three-dimensional shapes. These were used to target and destroy biofilms clogging enclosed tubes.


Regrowing dental tissue with stem cells from baby teeth

A successful Phase 1 clinical trial in China, co-led by School of Dental Medicine researcher Songtao Shi, paves the way for more widespread investigation into the utility of dental stem cells. metimes kids trip and fall, and their teeth take the hit. Nearly half of children suffer some injury to a tooth during childhood. When that trauma affects an immature permanent tooth, it can hinder blood supply and root development, resulting in what is essentially a “dead” tooth.

Until now, the standard of care has entailed a procedure called apexification that encourages further root development, but it does not replace the lost tissue from the injury and, even in a best-case scenario, causes root development to proceed abnormally. New results of a clinical trial, jointly led by Songtao Shi of the University of Pennsylvania and Yan Jin, Kun Xuan, and Bei Li of the Fourth Military Medicine University in Xi’an, China, suggest that there is a more promising path for children with these types of injuries: using stem cells extracted from the patient’s baby teeth. The work was published in the journal Science Translational Medicine.

“This treatment gives patients sensation back in their teeth. If you give them a warm or cold stimulation, they can feel it; they have living teeth again,” says Shi, professor and chair in the Department of Anatomy and Cell Biology in Penn’s School of Dental Medicine. “So far we have follow-up data for two, two and a half, even three years, and have shown it’s a safe and effective therapy.”

Shi has been working for a decade to test the possibilities of dental stem cells after discovering them in his daughter’s baby tooth. He and colleagues have learned more about how these dental stem cells, officially called human deciduous pulp stem cells (hDPSC), work, and how they could be safely employed to regrow dental tissue, known as pulp. 

The Phase 1 trial was conducted in China, which has a research track for clinical trials. The 40 children enrolled had each injured one of their permanent incisors, and still had baby teeth. Thirty were assigned to hDPSC treatment and 10 to the control treatment, apexification. Those who received hDPSC treatment had tissue extracted from a healthy baby tooth. The stem cells from this pulp were allowed to reproduce in a laboratory culture, and the resulting cells were implanted into the injured tooth. Upon follow-up, the researchers found that patients who received hDPSCs had more signs than the control group of healthy root development and thicker dentin, the hard part of a tooth beneath the enamel, as well as increased blood flow.

At the time the patients were initially seen, all had little sensation in the tissue of their injured teeth. A year following the procedure, only those who received hDPSCs had regained some sensation. Examining a variety of immune-system components, the team found no evidence of safety concerns. As further support of the treatment’s efficacy, the researchers had the opportunity to directly examine the tissue of a treated tooth when the patient re-injured it, and had to have it extracted. They found that the implanted stem cells regenerated different components of dental pulp, including the cells that produce dentin, connective tissue, and blood vessels.


How Dentists of the Future May Fix Your Teeth

The next time you lose a tooth, could your dentist just grow you a new one? Not yet, but research at USC brings dentists a step closer. Here are a few ways Herman Ostrow School of Dentistry of USCscientists could revolutionize dental care.

Rats and mice use their incisors—their two pairs of front teeth—to gnaw. The teeth would probably wear out if it weren’t for a peculiar fact: They never stop growing. That gives USC researchers some insight into regenerating teeth in humans. One day, a dentist might reach for a living tooth regenerated in a lab to replace a broken one.

A research team led by Yang Chai, associate dean of research at the Ostrow School and director of the Center for Craniofacial Molecular Biology, compared two kinds of stem cells in mice: stem cells that eventually lead to the growth of incisors and those that develop into molars, which stop developing in mice just as they do in humans. Learning how the stem cells differ may help scientists determine how to manipulate cells’ development to reactivate tooth growth.

The work means that, one day, a dentist might reach for a living tooth regenerated in a lab to replace a broken tooth, Chai says.

Janet Moradian-Oldak of the Ostrow School and her USC team may have found a secret to regrowing tooth enamel, the hardest substance in the human body.

Her research showed that the enzyme MMP-20, found in teeth, plays a key part in helping enamel grow correctly. That fits perfectly with the work of Qichao Ruan, a postdoctoral research associate at USC’s Center for Craniofacial Molecular Biology. Ruan developed a water-based gel that creates an enamel-like layer and repairs early tooth decay when placed on teeth. Its recipe includes a special protein known to interact with MMP-20, as well as a substance that comes from shellfish like shrimp and crab. The gel could be more effective in restoring the tooth than traditional crowns, whose adhesion weakens over time, Ruan says.

Don’t look for clinical trials yet, but Moradian-Oldak hopes one day their work will result in a gel-filled mouthguard worn overnight that could strengthen teeth and reduce their sensitivity.

After a tooth extraction, the gum surrounding the tooth’s root can be vulnerable to collapse. To prevent that, Neema Bakhshalian MS ’14, a periodontist and researcher at USC’s Laboratory for Immunoregulation and Tissue Engineering, worked with a team at the Ostrow School to develop an innovative rigid cage shaped like a tooth’s root. Called Socket-KAGE, it’s made of a unique resorbable material and can be immediately placed in the space left after a tooth is removed, helping the bones in the jaw repair without further surgery.


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