New Dental Material Resists Degradation | Chemical & Engineering News
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Web Date: September 28, 2015

New Dental Material Resists Degradation

Materials: A new dental-filling material is impervious to oral enzymes that break down conventional fillings and dental sealants
Department: Science & Technology | Collection: Life Sciences
News Channels: Materials SCENE, Organic SCENE, Biological SCENE
Keywords: dental composite, amalgam, saliva, esterase
A new ether-based resin for dental-filling composites performs better than standard ester-based resins, which are degraded by enzymes in the mouth.
Credit: Biomacromolecules
Chemical structure of ether-based resin for dental composite
A new ether-based resin for dental-filling composites performs better than standard ester-based resins, which are degraded by enzymes in the mouth.
Credit: Biomacromolecules

Dental materials used to fill cavities only last about 10 years before needing replacement because enzymes naturally present in saliva degrade them. Now researchers have synthesized a dental resin with a new chemistry that’s not affected by saliva enzymes and lasts longer than conventional resins in lab tests (Biomacromolecules 2015, DOI: 10.1021/acs.biomac.5b01069).

Composite materials, used for dental fillings and as sealants to protect teeth, contain a methacrylate polymer resin and a coupling agent that binds the polymer to the hydroxyapatite mineral at the surface of a tooth. The resin forms a matrix that holds in a filler material, such as a silicate; another coupling agent links the resin to the filler. This composite design was introduced in the 1960s to phase out amalgam fillings containing mercury. The composites avoid concerns over mercury toxicity (though they contain bisphenol A at levels deemed safe by the American Dental Association), and their color better matches the tooth. However, while mercury amalgams can last 30 or 40 years, composites typically fail after about a decade.

To improve the composite material’s lifetime, Jirun Sun, a chemist at the American Dental Association Foundation’s Anthony Volpe Research Center, in Gaithersburg, Maryland, decided to modify the chemistry of the resin. These methacrylate polymers contain ester groups, which are particularly vulnerable to hydrolysis and attack by abundant esterase enzymes produced by bacteria that live in the mouth.

Working with the original inventor of the composite dental materials, his colleague Rafael L. Bowen, Sun synthesized three ester-free versions of the resin. “We changed all the ester groups to ether groups, which are much stronger,” Sun says. They tested the new resins’ resistance to degradation by placing samples of the novel monomers and their polymers, as well as the standard methacrylate polymer, in solutions of two esterase enzymes found in saliva. After 16 days, one of the new polymers, TEG-DVBE, had lost none its mass or hardness. In contrast, the standard resin lost 2% of its mass, and its hardness dropped by 17%.

Sun says the group is now working on further testing the mechanical properties of the new polymer, and measuring how it holds up in actual saliva samples and when bacteria grow on it. “We’re confident it will withstand these challenges,” he says.

Carmem S. Pfeifer, a polymer chemist at Oregon Health & Science University, in Portland, praises the “sophisticated chemistry” of the new approach. She says both patients and dentists stand to benefit from longer-lasting dental materials.

Chemical & Engineering News
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Laura Henze Russell (September 30, 2015 9:16 PM)
It is time to address mercury toxicity from dental amalgam, which is particularly harmful to children and adults with genetic variants who do not methylate (clear toxins) well, who bioaccumulate it in their cells, triggering inflammation and fueling chronic diseases. There are many alternate filling materials. Any patient who suspects mercury is impacting their health should consult with a biologic dentist and functional medicine physician, and consider biocompatibility screening for dental materials to ensure that the replacement chosen is "right for you" and your immune system.

This is an issue for medical device safety across the board, as FDA regulations are 40 years old. It is time for Medical and Dental Device Safety Urgent Reform (MEDDSURGE), to call for a new framework of "Precision Devices" that are right for each patient.

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