Filling the gap

LSUHSC dentists are developing better biomaterials for fillings.

By Leslie Capo

Most of us have visited the dentist, found out we had a cavity, and gone through the sometimes painful experience of having a tooth filled. For some, the experience gets even worse-when a filling does not bond to the tooth properly and a gap develops around it, the result can be new decay and the need for an even larger filling.

Today, faculty members at the LSU Health Sciences Center in New Orleans' School of Dentistry are trying to fill this gap. They are working to develop new biomaterials that could make fillings more effective and save millions of dental patients money.

"Dental caries, or tooth decay, is the most common infectious disease," notes John Burgess, D.D.S., M.S., who is assistant dean of clinical research at the school. According to the World Health Organization's latest report, 5 billion people worldwide have dental decay. It's a big problem that needs a better solution.

As most people know, the treatment for a cavity is to remove the decay and fill the area with a dental filling material. These days, tooth-colored dental composite resins are widely used in restorative dentistry since they provide durable, natural-looking esthetic fillings. These fillings are bonded to the tooth with an adhesive, which is applied prior to the composite resin filling.

Even though most dentists use composites routinely, they have a number of drawbacks. For instance, composite resins shrink during the hardening process, creating spaces, or cracks, between the tooth and filling. When that happens, new decay can develop in the space between the tooth and the filling, requiring an even larger filling to restore the tooth. Improved dental adhesives may prevent or reduce that gap.

"Recurrent tooth decay is the most frequent cause for the failure of dental restorations or fillings," says Xiaoming Xu, Ph.D., assistant professor of operative dentistry and biomaterials. He is leading a new research project at the LSUHSC-NO dental school to develop new types of fluoride-releasing adhesives and sealants with improved sealing ability.

The dental school research team is working to develop new chemical compounds with improved adhesive as well as self-etching capabilities. The self-etching feature will reduce the time it takes to place the filling. The fluoride-releasing bonding agents based on the new compounds will release fluoride directly into the tooth structure and facilitate the transport of fluoride, rather than hinder it.

Fluoride, an effective decay-fighting agent, helps prevent new areas of decay from forming. Unfortunately, the adhesives used with current composite filling materials release little or no fluoride. In fact, today's dental bonding materials can actually form a barrier hindering the transport of fluoride from the restorative materials into the tooth.

"We are developing new ligands, or molecules, to build into the adhesive that will hold the fluoride, but not too tightly," said Burgess. "What happens now is that while you can get fluoride in, it is bound so tightly that it's difficult to get out. The compound we are working on will have a mechanism to hold the fluoride for a period of time and release it slowly. The mechanism will also allow the fluoride to be replenished when it's gone. It's a replacement mechanism rather than a decomposition mechanism."

Sealants-plastic coatings used to seal small pits and fissures in back teeth and prevent their future decay-are not now being used by many dentists because of a fear that the material will leak, allowing decay to progress undetected under the sealant until the cavity is very large.

"We are developing new monomers, or plastic materials, that we will blend into existing sealants to make them self-adhesive," said Xu. "These new monomers will have improved wetting, to bond directly to the tooth, saving steps which will not only save time, but also reduce the chance for contamination."

Sealants containing the new compounds will not only adhere to tooth enamel better, they will have improved fluoride-releasing capacity as well as the ability to be "recharged" with fluoride-that is to replace the fluoride after the original amount has been released. This means that the anti-decay effects will last for the life of the filling.

One of several projects funded by a $10.7 million grant from the National Institutes of Health's Centers of Biomedical Research Excellence (COBRE) Program, the research has major potential for future technology transfer. The researchers at LSUHSC School of dentistry believe the technology will be patentible, and the new products developed could be used by dentists worldwide.