Dentures can bring back the smile of people who have lost teeth because of aging, injury, or disease. But the majority of denture wearers are bound to cope repeatedly with a condition called dental stomatitis, or thrush. The gums under the denture become sore and inflamed, due to infection from the fungus known as candida.
Good oral hygiene can help. But many denture wearers—because of advanced age or other factors—are not able to keep up with a rigorous regimen.
Enter a team at the Geriatric Research, Education and Clinical Center at the South Texas VA Health Care System.
Working with a polymer chemist in Massachusetts, they are developing a new type of denture that fights stomatitis. It looks and feels like the standard product. But it has a secret weapon built in: It releases, over time, a drug that kills the fungus.
"If it passes clinical testing, we envision this technology being applied to all new dentures."
In lab tests reported earlier this year in the journal Oral Diseases, the experimental product showed strong action against candida for up to 30 days—after which the device could be "recharged" with a fresh dose of drugs to renew its attack on the fungus.
'Rechargeable' aspect is key
The "rechargeable" aspect is central to the work, says Dr. Chih-Ko Yeh, a geriatric dentist with VA in San Antonio.
"Antifungal agents have been added into denture formulations in the past by other groups," he says, "but the antifungal duration was short, because once the added drugs were released, no new antifungal agents could be added to the denture."
Yeh's main collaborator is Dr. Yuyu Sun, a polymer chemist now at the University of Massachusetts Lowell. It was Sun who came up with the idea for long-term anti-candidal dentures. Yeh's team is providing the clinical expertise to bring the product, now seven years in the works, to fruition.
"I commonly manage patients with denture infections," says Yeh. He notes that while candidal infection is a global problem for denture wearers, VA patients are more likely than the general population to wear dentures in the first place—one VA survey in Boston, for example, found that half of elderly male Veterans in that area wore dentures. And once they are fitted with the appliances, they tend to be more likely to have risk factors for stomatitis.
Yeh explains that "many of them are medically and immunologically compromised," the result of various health conditions and the treatments that come along with them, such as antibiotics and steroid drugs.
Why can't denture wearers simply apply a drug topically to their dentures every morning when they put them in? Wouldn't that be a low-tech solution to the problem?
Actually, that is one of the current treatments for stomatitis. But it doesn't work that well, says Yeh, who has a Ph.D. in oral biology in addition to his dental degree.
"There are antifungal mouth rinses and topical remedies. But using anti-candidal topical treatment is not very effective due to the short effectiveness period, and problems associated with patient compliance, especially for elderly who have physical or mental disabilities."
Figuring out the best materials
Right now, his group is working with Sun to figure out the best combination of materials for the rechargeable denture.
In the study reported recently in Oral Diseases, they used a grafting, or "plasma," approach. They started with pre-made acrylic denture resin and coated it with a different material that could serve as a medium for the drug. The coating material was a water-soluble polymer known as PNVP, already used widely in pharmaceuticals. Discs made of the two fused materials were soaked in a solution containing the medicine—in this case the antifungal drug miconazole. The team then immersed the discs in human saliva, and in a saline solution that mimics the human body's chemical environment. They measured how well the discs released the drug over time.
In other experiments, they have used a chemical technique called copolymerization—another way to get PNVP into the denture material. "Copolymerization adds PNVP to the resin monomer," explains Yeh. Only then is the denture manufactured. The PNVP is distributed evenly throughout its base, as opposed to being added only to the surface.
"Currently, we are determining which materials—including PNVP—can provide the best results for carrying anti-candidal drugs without affecting the mechanical properties of the denture base materials," says Yeh.
There's still a long road ahead for the researchers. After determining the best procedures for drug loading and release, with no adverse impact on the core properties of the denture, they have to test the model in "clinically authentic dentures," and then in animal models. The last stage in the research will be a clinical trial, most likely with Veteran denture wearers in San Antonio.
Yeh envisions the new type of denture being prescribed routinely, in a preventive manner, and not only for those who have already shown a pattern of infections.
"If it passes clinical testing, we envision this technology being applied to all new dentures. Candida-associated denture stomatitis is such a common problem for denture wearers that it will likely impact almost all of them at some point."
And in the much-ballyhooed era of precision medicine, Yeh is quick to point out that the product could be the "first personalized therapeutic denture."
"If a yeast [candida] infection is present, the denture can be charged with antifungal drugs to initiate therapy. When the infection clears, the anti-candidal denture can be treated with quenching agents to 'wash out' the remaining anti-candidal agents still bound to the denture surface, and the device can continue to be used as a conventional denture. If infection reoccurs, anti-candidal agents—either the same drug, or a different one from a different class, to avoid drug resistance—can be recharged onto the denture to restart therapy."
The work is funded by VA and the National Institutes of Health. A related patent is held by the University of South Dakota, where Sun previously conducted his research.