Having navigated Halloween and now facing Thanksgiving in the United States, and with the December holidays around the corner worldwide, the annual battle of tooth versus sugary treat has begun. Diligently toiling to repair the inevitable cavities is Stefan Habelitz, a researcher at the University of California, San Francisco’s School of Dentistry.
Habelitz has been studying the wondrous and often complicated production of tooth enamel, our first line of defense against tooth decay. Tooth enamel is as thick as a dime, highly-mineralized, and can withstand an immense amount of pressure (up to 250 kg/mm2). It consists of hair-thin, fibrous and densely packed crystalline rods gathered to shape a tooth’s crown. Despite its strength, increased consumption of sugary and acidic foods, and social behavior, has a corrosive effect on the structure of tooth enamel.
Habiltz’s research focuses on the formation of enamel’s crystalline rods — a process that, if replicated successfully in vitro, could revolutionize restorative dentistry.
The formation of tooth enamel essentially creates minerals in your mouth.
The process starts as recombinant protein, called amelogenin, which forms in the mouth and self-assembles into peptide bracelets that initiate and control, molecule by molecule, the growth of calcium phosphate crystals. Amelogenin determines crystal size and direction of growth, forming nanospheres that gather into ribbon-like nanofibers.
These nanofibers in turn form into hair-thin rods that are packed together over the shape of the tooth. Protein is extracted from the mineralized tissue in the final stages of tooth enamel production, leaving behind a substance that is 98 percent mineral and 2 percent protein and lipid. Formation of enamel over a tooth’s crown takes roughly four years, and is the only material in the body that undergoes an organic to inorganic conversion.
But teeth aren’t solid enamel; just beneath a tooth’s enamel lies something called dentin. It is less mineralized and less brittle than enamel and consists of 70 percent calcium phosphate, 20 percent protein and lipids, and 10 percent water. Another part of Habelitz’s research is focused on finding mechanisms to deliver calcium phosphate to tooth dentin after a cavity.
Replicating these processes in a test tube is an arduous task that requires vigilance over lab-simulated growth conditions. Habelitz and his team have only progressed through the nanoribbon phase in enamel production, but he remains optimistic.
“If you have a protein structure that directs the crystal growth, now you can use the protein as a template to create mineralized structures,” he said. “[You can] control and manipulate the growth of the organic phase … you can control the growth of the inorganic. That can grow into micro and macro structures. [It will] eventually allow us to make very unique structures that we haven’t been able to make.”
One obvious benefit of his work would lie in creating a novel replacement for the gold and amalgam used in dental fillings, essentially repairing teeth instead of patching them.
“We still have to figure out how to attach the [remineralized dentin and synthetic enamel],” Habelitz said. “They grow away from each other in vitro. [Adhesives] are pretty good, but they don’t last forever. So, that’s the challenging part.”
Meanwhile, his research may have applications beyond teeth
Synthetic enamel’s unique structure, durability and scale offer interesting prospects in the world of biomaterials and bioengineering. Joanna Aizenberg, a researcher at the Bell Laboratories, has already used the process of self-assembly in research for microelectromechanical switches. Enamel’s future in electric circuitry may yield results at dimensions we have yet to see.
Despite being on the bicuspid of dental innovation, Habelitz is leery of the commercial market. Dentists and dental researchers are tied to the demands of a culture that favors healthy-looking teeth over healthy teeth. (Americans spent $2.75 billion dollars on cosmetic dental procedures in 2007 and spend nearly $2 billion every year whitening their teeth.) “Overall, that idea of beauty is so important in dentistry that it really affects the treatment of people,” said Habelitz. “Dentists kind of have that conflict. You don’t always provide the best medical care because you have all these aesthetic requirements.”
Still, with commercial and bioengineered application of synthetic enamel and remineralized dentin still years out, there is no downplaying the importance of a strict regimen of proper dental hygiene this holiday season, and year-round.