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Aug. 4, 2005

Researchers synthesize tooth enamel's structure in the lab

Hydroxyapatite nanorods, 400 nm

ANN ARBOR, Mich.—Researchers at the University of Michigan have created crystals that can be organized into a structure that mimics enamel of human teeth, a step toward creating fillings to replace the material that's been destroyed.

Research investigator Haifeng Chen's laboratory creation is reported in an article in the current issue of the Journal of Colloid and Interface Science.

Chen uses a simple idea to explain why he's excited about simulating the hard, white exterior of teeth. "If you have a cavity and you have two choices of a material to fill a tooth in your mouth—one that's similar to what's in your own teeth, and one that's not—which would you choose?"

Materials now used to fill cavities all have some drawbacks. For example, porcelain is very hard, which helps it last but also causes wear on teeth that come into contact with one that's been filled. Real enamel contains fluoride and acts as a reservoir of the naturally occurring compound that can help fight tooth decay. Synthesized enamel would mimic that ability.

Brian Clarkson, chair of cariology, restorative sciences and endodontics and the Clifford T. Nelson Professor of Dentistry, is senior author on the paper. He and Chen, a research investigator at the School of Dentistry, worked on the project with Kai Sun and John Mansfield at the U-M Electron Microbeam Analysis Laboratory, where Chen also has an appointment.

Clarkson and Chen met while Clarkson was on sabbatical a few years ago in Leeds, England. "I was very impressed with him—not just his technical ability, but his thought processes. He thinks very well outside of the box," Clarkson said of the young nanotechnology chemist.

Later, when Chen came to U-M, he visited Clarkson holding a journal article about barium chromate crystals. "He pointed to the picture and said, 'what do these look like to you?' And I said, 'they look like enamel crystals.' He said, 'I can make that in the lab.'"

True to his word, Chen quickly created crystals in the lab with the same chemical composition as natural enamel. "I'd never seen single enamel crystals made in the lab. I was totally impressed," Clarkson recalled.

The next step was organizing individual crystals into a prism, sort of like taking individual bricks and building them into a wall.

"Enamel is special—the cells in the mature enamel are already dead, unlike bone or skin. Mature enamel is pure chemicals, so we think there might be a pure chemical way to create enamel," Chen said.

Tooth structure, as drawn by Haifeng Chen. Enamel is the outside layer of the tooth, the white surface we associate with a healthy smile. More images >

From building a prism, Chen and Clarkson now want to build realistic enamel structures.

Clarkson believes it's possible they could have an enamel-like composite within a year, and produce crowns suitable for repairing decayed teeth within about four years. Perhaps even before crowns, they could produce thin films that could act as a sort of enamel bandage over a cavity that's just begun.

Application of synthetic enamel isn't limited to filling cavities. Clarkson said he sees potential for use in bone repair and bone augmentation. For example, if someone is in an accident and has a bone damaged beyond what the body can naturally repair, adding synthetic crystals could help heal it.

"Enamel is the hardest substance in the body," Clarkson said. "If we can make a similar structure to it, we can find many applications for it."

Dentists have long worked on finding better, more durable ways to fill cavities in teeth—from stone chips to metals and amalgams. Synthesizing enamel is just one way researchers at the U-M School of Dentistry are continuing this work on better materials for healing wounds, including growing tongue tissue in a Petri dish and working on tissue-engineered bone implants infused with therapeutic genes to help spur growth of new supporting tissue.

The Chen/Clarkson collaboration is funded by the National Institute of Dental and Craniofacial Research, part of the National Institutes of Health, U-M's Technology Transfer office has filed a patent application on the process with which to manufacture these crystals.

Related links:

Clarkson's faculty profile

Journal of Colloid and Interface Science

Chen participated in a regenerative medicine showcase at U-M in May; read a synopsis of his work in this PDF of the program

U-M Tech Transfer

Contact: Colleen Newvine
Phone: (734) 647-4411