New materials designed to fight pathogens, reduce caries

By Lori Roniger, associate editor

March 30, 2017 -- The development of secondary caries and bacterial acid formation leads to many dental restoration failures. However, researchers are concocting clever new polymer-based dental materials, some of them engineered to be "smart," to combat such problems.

During a session on polymer-based materials on March 23 at the International Association for Dental Research (IADR) annual meeting in San Francisco, investigators gave presentations on their research in developing materials with the following attributes:

“We're trying to remove the root causes of tooth decay by suppressing the bacteria that cause tooth decay.”
— Huakun Xu, PhD
  • The ability to remineralize
  • The activation of an antibacterial agent when pH is low
  • Inhibition of periodontitis-related pathogens and biofilm

"We're focusing on regenerating the lost minerals," Huakun Xu, PhD, a professor at the University of Maryland School of Dentistry in Baltimore, told "We're trying to remove the root causes of tooth decay by suppressing the bacteria that cause tooth decay."

He gave a talk about his research on the novel dimethylaminohexadecyl methacrylate (DMAHDM) nanocomposite, which shows promise for reducing recurrent caries in composite restorations and as class V restorations to fight periodontitis.

Material whirl

Xu's research team developed a nanocomposite containing DMAHDM and nanoparticles of amorphous calcium phosphate (NACP) and examined its ability to inhibit both dental plaque microcosm biofilms and periodontitis-related biofilms.

The research with these materials directly addresses secondary caries (a common cause of restoration failure), root caries (increasing as the population ages), and class V restorations with subgingival margins (difficult to clean and precede periodontitis).

Image of Huakun Xu, PhD, at IADR podium
Huakun Xu, PhD, from the University of Maryland presents at IADR 2017.

The researchers exposed a nanocomposite with and without DMAHDM to dental plaque microcosm biofilms containing six periodontitis-related pathogens: Porphyromonas gingivalis, Prevotella intermedia, Prevotella nigrescens, Aggregatibacter actinomycetemcomitans, Fusobacterium nucleatum, and Enterococcus faecalis. The biofilms were inoculated with human saliva.

There were significantly fewer human saliva microcosm biofilm colony-forming units and periodontal pathogens, as well as significantly less biofilm biomass, on the DMAHDM composite than on the control composite, Xu and colleagues found. At the same time, they found the mechanical properties of the DMAHDM composite to be similar to those of the commercial control composite.

They concluded that their DMAHDM-NACP nanocomposite demonstrated strong inhibition against human saliva microcosm biofilm and periodontitis-related pathogens.

Xu said their nanocomposite shows promise for reducing recurrent caries in composite restorations and combating periodontitis in class V restorations, along with other restorative and preventive uses.

Smart agent

During another presentation at the IADR session on polymer-based materials, Yin Yang, PhD, a postdoctoral fellow at the ADA Foundation in Gaithersburg, MD, discussed the novel "smart" antibacterial agent her research team has developed that could be incorporated into resin composites and adhesives to help prevent secondary caries without potential drug resistance.

The smart agent is designed to be activated when the environment becomes acidic, such as during the accumulation of biofilm that can cause tooth decay and secondary caries. A substance that increases its antibacterial efficacy in acidic conditions will cause fewer problems for oral microbes, prevent damage to teeth and restorations, and avoid the overuse of antibiotics, according to Yang, whose background is in chemistry.

Yang and colleagues synthesized a quaternary pyridinium salt (QPS) with a pH-sensitive antimicrobial capability. They tested the antibacterial activity of QPS against Escherichia coli and Streptococcus mutans, and found that its minimum inhibitory concentration (MIC) against S. mutans increased by eightfold when the environment pH dropped from 6.8 to 4.6 and by sixteenfold against E. coli.

"We have developed a pH-sensitive antibacterial agent," she concluded.

Copyright © 2017

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