Researchers at the University of Southern California's School of Dentistry are closing in on making tooth enamel, the hardest substance found in vertebrates. They have identified tiny spheres that regulate the formation and organization of tooth enamel by controlling the substance's crystalline growth.
Called nanospheres because they are only 20 nanometers in diameter, these structures are formed by a naturally occurring family of tooth-specific proteins known as amelogenins. These spheres are also a component of the synthetic amelogenin first cloned at the USC School of Dentistry's Center for Craniofacial Molecular Biology (CCMB) four years ago.
"More than 98% of tooth enamel consists of carbonated calcium hydroxy-apatite," says CCMB research professor A.G. Fincham, Ph.D. "Essentially, your teeth are made of rock."
For two decades, CCMB researchers have been studying tooth enamel with the goal of one day replacing mercury-based gold and silver fillings with restorations of man-made material identical or similar to natural tooth enamel. "Beyond that, the same principles that nature uses to make enamel might also be applied to create novel synthetic materials," Dr. Fincham says.
Tooth enamel begins to form in the human embryo when a specialized layer of cells, called ameloblasts, in the embryonic tooth bud secretes amelogenin proteins. The amelogenins self- assemble to form the extracellular matrix within which the inorganic crystals of mineral start to form. "The earliest enamel crystals form in extremely long, thin ribbons and are rather beautifully parallel," Fincham notes.
CCMB researchers first saw the spheres in 1994. "Magnified in an electron microscope, they looked like tiny ping pong balls among the long ribbons of crystal," Fincham reports.
A more powerful atomic force microscope recently revealed that the spheres are
uniformly 18 to 20 nanometers in diameter.
(A nanometer is a billionth of a meter, and a 20-nanometer- di
Contact: Bob Calverley
University of Southern California