Dr. Antonucci, a polymer chemist with the National Institute of Standards and Technology in Gaithersburg, Md., and Dr. Drago Skrtic, a physical chemist with the American Dental Association Health Foundation, Paffenbarger Research Center, located on the NIST campus, are working on a dental composite that can actually cause teeth to repair their own small cavities. Antonucci reported on their research at the 222nd national meeting of the American Chemical Society, the world’s largest scientific society.

"We’ve tested it [in vitro] as a remineralizing sealant for artificially induced caries in bovine enamel and we’ve been able to see the growth of new mineral," Antonucci said in a telephone interview. Demineralization of teeth is what leads to cavities (caries). The composite materials he is working with contain amorphous calcium phosphate, or ACP for short, as a bioactive filler.

ACP releases calcium and phosphate ions, which "in the right proportions, can form the natural mineral [hydroxyapatite] that is found in teeth and bones."

While researchers have known for several years about ACP’s restorative powers, the NIST/ADA research group is unique in trying to put the material into a bioactive and photocurable polymer composite that could have multiple dental applications. The polymer in the composites can be designed to be biostable or biodegradable, depending on the intended application.

"We are designing a specific material right now, which the American Dental Association believes can be used as an orthodontic adhesive," said Antonucci. "One of the problems with using orthodontics in children’s mouths is that where they’re attached to teeth by braces, there tends to be demineralization around that tooth. Using this kind of adhesive material that has the ability to remineralize the tooth, or at least to prevent demineralization, we believe can be a distinct advantage."

Dr. Gary Schumacher, a dentist and research colleague of Antonucci and Skrtic, agrees. "I think traditionally one of the biggest problems that the orthodontic patient has is keeping their teeth clean. The brackets, attached to teeth to hold the orthodontic wires and elastics, also trap food and plaque, which promotes demineralization and the decay process. What we would have then are the building blocks for remineralization to reverse the decay process." Schumacher is the chief of clinical research for the Paffenbarger Research Center.

Another potential application for an ACP composite is as a remineralizing liner or base material in dental fillings, especially to protect against secondary cavities that can form under or adjacent to conventional fillings. "It’s probably the biggest problem facing most dentists today," according to Schumacher. He estimates more than half of the fillings done by dentists are necessitated by secondary tooth decay. Conventional fillings only seal off the cavity; they do not contain materials that can cause the tooth to repair itself.

Root canal therapy is another area where ACP could be useful, noted Schumacher. "As a filling material or sealer for endodontics, it’s absolutely perfect because of its potentially superior biocompatibility compared to currently used materials. It’s ideal."

ACP will not cause a tooth to completely regenerate itself. "It’s designed to remineralize small cavities," Antonucci pointed out. "We don’t think it’s going to work with a large cavity because it only repairs small holes and is not as strong or hard as conventional filling materials, such as ceramic and glass." Antonucci does not expect ACP to replace current bioinert fillings. "We don't envision it as a permanent filling. If we use it as a liner or base, then we would put a regular filling over it." Potentially stronger hybrid ACP composites with reinforcing glass fillers are under study, the researchers noted.

ACP might also be used as a sealant over white spots on teeth, according to Antonucci. A white spot can be an indication of incipient caries — the beginning stage of a cavity. The spots can contain small fissures where food particles can accumulate and cause cavities.

Yet another potential future application for a biodegradable ACP composite is delicate bone repair, such as in facial reconstruction, and fractures. "Long-term, we envision our material in tissue engineering applications where you want to remineralize defects in bone with injectable, biodegradable, polymer-based composites," said Antonucci.

Among dentists who know about ACP, "there's a certain level of excitement," Schumacher noted. "But," he added, "I think the general dentist, the practicing dentist, knows very little about it. I don't think we're getting the message out well enough."

ACP already has been commercially used in toothpaste and chewing gum, and the NIST/ADA group has been able to incorporate it into a biostable composite that could be used as a temporary filling or a dental adhesive. The researchers are looking at the feasibility of incorporating ACP into biodegradable composites.

Antonucci hopes to be able to do that and start clinical trials in about a year.