Nanocomposites for improved dental fillings

Scientists at the American Dental Association’s Paffenbarger Research Center have shown that nanotechnology can produce tooth fillings that are stronger than any currently available fillings, and more effective at preventing secondary decay.

Standard fillings are made by mixing a liquid resin with a powder that contains colouring, reinforcement and other materials. The resulting paste is then packed into the cavity, and the tooth illuminated with a light that causes the paste to polymerise and harden.

For decay-fighting fillings, an additive is included in the powder to provide a steady release of calcium and phosphate ions. However, the available additives are structurally weak, to the point where they compromise the filling as a whole.

A calcium phosphate nanocomposite filling in a tooth (© NIST)

The solution devised by Hockin Xu and his colleagues is a spray-drying technique that yields particles of several ion-releasing compounds, one of which is di-calcium phosphate anhydrous, or DCPA. The particles are around 50 nm across, which is some 20 times smaller than the micrometre-scale particles in a conventional DCPA powder.

With their much higher surface to volume ratio, the nanoparticles are more effective at releasing ions. Less of the material is therefore required to produce the same effect, and there is more room in the resin for reinforcing fibres that strengthen the filling. With specially-produced silica-fused fibres, the new nanocomposite resin is nearly twice as strong as standard fillings.

“Adding silicon nitride whiskers increases strength, and adding calcium phosphates helps reverse tooth decay,” says Jason Griggs, a biomaterials expert at the Texas A&M Health Science Center. “These are innovative ideas that promise to greatly improve the usefulness of dental composite.”

“We need to further optimise nanoparticle sizes and compositions, and optimise reinforcement fillers in the resin,” says Xu. “We also need to perform long-term tests to determine composite durability.”

Once these tests have been completed, clinical trials will be required before the new nanocomposite becomes part of the dentists’ standard armoury against tooth decay.

Figure: A calcium phosphate nanocomposite filling in a tooth (© NIST).

Further reading: Effects of Calcium Phosphate Nanoparticles on Ca-PO4 Composite, Xu et al., J. Den. Res. 86, 378 (2007).

Article first published in Nanomaterials News.