Blocking yeast-bacteria interaction may prevent severe biofilms that cause childhood tooth decay

Though most tooth decay can be blamed on bacteria, such as Streptococcus mutans, the fungus Candida albicans may be a joint culprit in an alarmingly common form of severe tooth decay affecting toddlers known as early childhood caries.

In earlier research, a team from the University of Pennsylvania School of Dental Medicine had found that C. albicans, a type of yeast, took advantage of an enzyme produced by S. mutans to form a particularly intractable biofilm. In a new study, the researchers have pinpointed the surface molecules on the fungus that interact with the bacterially-derived protein. Blocking that interaction impaired the ability of yeast to form a biofilm with S. mutans on the tooth surface, pointing to a novel therapeutic strategy.

"Instead of just targeting bacteria to treat early childhood caries, we may also want to target the fungi," said Hyun (Michel) Koo, senior author on the study and a professor in the Department of Orthodontics and Divisions of Pediatric Dentistry and Community Oral Health. "Our data provide hints that you might not need to use a broad spectrum antimicrobial and might be able to target the enzyme or cell wall of the fungi to disrupt the plaque biofilm formation."

Koo collaborated on the work with Penn Dental's Geelsu Hwang, the first author and a research assistant professor, as well as Yuan Liu, Dongyeop Kim and Yong Li. Damian J. Krysan of the University of Rochester was also a coauthor.

The research appears in the journal PLOS Pathogens.

Candida can't effectively form plaque biofilms on teeth on its own nor can it bind S. mutans, unless in the presence of sugar. Young children who consume sugary beverages and foods in excess are at risk of developing early childhood caries. Koo's team had previously discovered that an enzyme, GftB, secreted by S. mutans, uses sugar from the diet to manufacture glue-like polymers called glucans. Candida promotes this process, resulting in a sticky biofilm that allows the yeast to adhere to teeth and to bind to S. mutans.

The researchers suspected that the outer portion of the Candida cell wall, composed of molecules called mannans, might be involved in binding GftB. To gain a more detailed understanding of the interaction between the yeast and the enzyme, the researchers measured the binding strength between various mutant Candida strains and GtfB using biophysical methods. Such measurements were developed by Hwang, who has a background in engineering and is applying his unique expertise to advance dental science.

Koo, Hwang and colleagues found that the enzyme bound much more weakly to mutants that lacked components of the mannan layer than the wild-type Candida. The team next looked at the abilities of the mutant Candida to form biofilms with S. mutans in a laboratory assay. The mutants that had impaired binding with GftB were mostly unable to form biofilms with S. mutans, resulting in significantly fewer Candida cells and reduced production of the sticky glucans molecules.

Using another biophysical technique, the researchers tested how stable the biofilms were when attached to a tooth-like surface. While low-shear stress, roughly equivalent to the force generated by taking a drink of water, removed only a quarter of the wild-type biofilm, the same force removed 70 percent of the biofilms with mutant Candida. When the forces were increased to the equivalent of a vigorous mouth rinse, the mutant biofilms were almost completely dislodged.

To ensure their findings translated to in vivo conditions, they examined biofilm formation in a rodent model that can mimic the development of early childhood caries. When animals were infected with both S. mutans and either the wild type or defective mutant yeast strains, the researchers observed clear differences. While biofilm formation was abundant if the wild-type yeast was used, it was substantially reduced in animals infected with the mutant strain. A more precise analysis revealed that the these defective biofilms completely lacked viable Candida cells and S. mutans were reduced by more than five-fold.

The findings point to a new direction for treatment of early childhood caries. The current standard of care, beyond the use of fluoride as a preventive approach, is to target only the bacteria with antimicrobials, or to use surgical interventions if the tooth decay has become too severe.

"This disease affects 23 percent of children in the United States and even more worldwide," said Koo. "In addition to fluoride, we desperately need an agent that can target the disease-causing biofilms and in this case not only the bacterial component but also the Candida."

Koo and colleagues are now working on novel therapeutic approaches for targeted interventions, which can be potentially developed for clinical use.

Visiting virtual beach improves patient experiences during dental procedures

Imagine walking along a South Devon beach on a lovely day. The waves are lapping on the shore, rabbits are scurrying in the undergrowth, and the bells of the local church are mingling with the calls of the seagulls. Then, as you turn to continue along the coast path feeling calm and relaxed you suddenly hear your dentist say "Fine, all done, you can take the headset off now". For patients at one dental practice in Devon, England, such Virtual Reality encounters are resulting in demonstrably better experiences in the dentist's chair. 

A link to what the patient sees is here - https://youtu.be/n5kjETt8cZI.

In a study published today (Wednesday 14th June 2017) in the journal Environment & Behaviour, a team of researchers at the Universities of Plymouth, Exeter and Birmingham worked with Torrington Dental Practice in Devon to find out whether experiences like these could improve the patient's experience during routine dental procedures, such as fillings and tooth extractions. 

Patients, who had agreed to take part in the study were randomly allocated to one of three conditions: a) standard care (i.e. normal practice), b) a virtual walk around Wembury beach in Devon (using a headset and handheld controller), or c) a walk around an anonymous virtual reality city. Results found that those who 'walked' around Wembury were less anxious, experienced less pain, and had more positive recollections of their treatment a week later, than those in the standard care condition. These benefits were not found for those who walked around the virtual city. 

Dr. Karin Tanja-Dijkstra was the lead author of the study. She said: "The use of virtual reality in health care settings is on the rise but we need more rigorous evidence of whether it actually improves patient experiences. Our research demonstrates that under the right conditions, this technology can be used to help both patients and practitioners."

The authors of the research stress that the type of virtual reality environment the patient visits is important. Virtual Wembury was created by Professor Bob Stone and colleagues at the University of Birmingham, and the fact that only patients who visited Wembury, and not the virtual city, had better experiences than standard care is consistent with a growing body of work that shows that natural environments, and marine environments in particular, can help reduce stress and anxiety. 

Co-author Dr. Mathew White from the University of Exeter explained: "We have done a lot of work recently which suggests that people are happiest and most relaxed when they are at the seaside. So it seemed only natural to investigate whether we could "bottle" this experience and use it to help people in potentially stressful healthcare contexts." 

Dr Sabine Pahl, the project's coordinator at the University of Plymouth, added: "That walking around the virtual city did not improve outcomes shows that merely distracting the patients isn't enough, the environment for a patient's visit needs to be welcoming and relaxing. It would be interesting to apply this approach to other contexts in which people cannot easily access real nature such as the workplace or other healthcare situations."

The Torrington Practice dentist involved in the research, Melissa Auvray, agreed: "The level of positive feedback we got from patients visiting Virtual Wembury was fantastic. Of course, as dentists we do our very best to make the patient feel as comfortable as possible but we are always on the look out for new ways to improve their experiences." 

Professor David Moles from the University of Plymouth added "This research is one of a number of initiatives we at Plymouth University Peninsula School of Dentistry have been working on alongside the fabulous team at Torrington Dental Practice and it clearly demonstrates the benefits that can be achieved when academics work in partnership with clinicians in order to address problems that really matter to patients."

The team are hoping to now investigate whether Virtual Wembury can help patients in other medical contexts and whether certain additions to the virtual environment could make the experience even better.

Study: Use of prefabricated blood vessels may revolutionize root canals

While root canals are effective in saving a tooth that has become infected or decayed, this age-old procedure may cause teeth to become brittle and susceptible to fracture over time. Now researchers at OHSU in Portland, Oregon, have developed a process by which they can engineer new blood vessels in teeth, creating better long-term outcomes for patients and clinicians.

Their findings will publish online in the journal Scientific Reports on June 12, 2017. 

More than 15 million root canals are conducted annually in the United States. The current procedure involves removing infected dental tissues and replacing them with synthetic biomaterials covered by a protective crown. 

"This process eliminates the tooth's blood and nerve supply, rendering it lifeless and void of any biological response or defense mechanism. Without this functionality, adult teeth may be lost much sooner, which can result in much greater concerns, such as the need for dentures or dental implants," says principal investigator Luiz Bertassoni, D.D.S., Ph.D., assistant professor of restorative dentistry in the OHSU School of Dentistry, and assistant professor of biomedical engineering in the OHSU School of Medicine.

To address this issue, Bertassoni and colleagues used a 3D printing-inspired process -- based on their previous work fabricating artificial capillaries -- to create blood vessels in the lab. They placed a fiber mold made of sugar molecules across the root canal of extracted human teeth and injected a gel-like material, similar to proteins found in the body, filled with dental pulp cells. The researchers removed the fiber to make a long microchannel in the root canal and inserted endothelial cells isolated from the interior lining of blood vessels. After seven days, dentin-producing cells proliferated near the tooth walls and artificial blood vessels formed inside the tooth.

"This result proves that fabrication of artificial blood vessels can be a highly effective strategy for fully regenerating the function of teeth," says Bertassoni, who also serves as an honorary lecturer in Bioengineering at University of Sydney-School of Dentistry. "We believe that this finding may change the way that root canal treatments are done in the future."

Common periodontal pathogen may interfere with conception in women

According to a study carried out at the University of Helsinki, Finland, a common periodontal pathogen may delay conception in young women. This finding is novel: previous studies have shown that periodontal diseases may be a risk for general health, but no data on the influence of periodontal bacteria on conception or becoming pregnant have been available.

"Our results encourage young women of fertile age to take care of their oral health and attend periodontal evaluations regularly", says periodontist and researcher Susanna Paju, University of Helsinki.

Study population comprised 256 healthy non-pregnant women (mean age 29.2 years, range 19 to 42) who had discontinued contraception in order to become pregnant. They were enrolled from the general community from Southern Finland. Clinical oral and gynecological examinations were performed. Detection of major periodontal pathogens in saliva and analysis of serum and saliva antibodies against major periodontal pathogens as well as a vaginal swab for the diagnosis of bacterial vaginosis at baseline were carried out.

Subjects were followed-up to establish whether they did or did not become pregnant during the observation period of 12 months.

Porphyromonas gingivalis, a bacterium associated with periodontal diseases, was significantly more frequently detected in the saliva among women who did not become pregnant during the one-year follow-up period than among those who did. The levels of salivary and serum antibodies against this pathogen were also significantly higher in women who did not become pregnant.

Statistical analysis showed that the finding was independent of other risk factors contributing to conception, such as age, current smoking, socioeconomic status, bacterial vaginosis, previous deliveries, or clinical periodontal disease.

Women who had P. gingivalis in the saliva and higher saliva or serum antibody concentrations against this bacterium had a 3-fold hazard for not becoming pregnant compared to their counterparts. Increased hazard was nearly to 4-fold if more than one of these qualities and clinical signs of periodontitis were present.

"Our study does not answer the question on possible reasons for infertility but it shows that periodontal bacteria may have a systemic effect even in lower amounts, and even before clear clinical signs of gum disease can be seen", says Dr. Paju. "More studies are needed to explain the mechanisms behind this association."

Infertility is a major concern, and increasing healthcare resources are needed for infertility treatments. More attention should be paid to the potential effects of common periodontal diseases on general health. Young women are encouraged to take care of their oral health and maintain good oral hygiene also when they are planning pregnancy, suggests Dr. Paju.