The difference in bone and enamel microstructure is attributed to a key protein in enamel that molds crystals into strands thousands of times longer and much stronger than those in bone. The dimension of an enamel strand is 100,000 by 50 by 25 nanometers; bone is 35 by 25 by 4 nanometers.
But how that protein achieves this feat of crystal-strand shape-shifting has remained elusive. Today, scientists have reported the first direct observation of how this protein, amelogenin, interacts with crystals like those in bone to form the hard, protective enamel of teeth.
The study, published by a team from the Department of Energys Pacific Northwest National Laboratory and the University of Southern California on Friday (Sept. 24) in Journal of Biological Chemistry, identifies the region of the protein that interacts with the enamel crystals. The results explain how 100 nanometer spheres of amelogenin cluster like bowling balls around developing enamel crystals, forcing the crystals to elongate into thin, weaved strands that endow enamel with the strength of steel.
The discovery is a milestone for those who would wish to nano-engineer tissues, implants and synthetic coatings based on natures rules.
The proteins determine the crystal structure, said Wendy J. Shaw, lead author and PNNL staff scientist. Like bone, teeth are made of HAP, but the proteins present when teeth form create enamel, a material with entirely different properties from bone. If you can control the interactions between proteins and crystals, the same principal can be applied to nano-patterning and nano-building.
Shaws co-authors are PNNL chief scientist Allison A. Campbell and Michael L. Paine and Malcolm L. Snead of USCs Center for Craniofacial Molecular Biology in Los Angeles.