In 1781, the soon-to-be U.S. president George Washington wrote to his doctor requesting “a pair of pincers to fasten the wire of my teeth.”
His “teeth” were false and had been hand-carved from hippopotamus ivory and cow’s teeth, then fastened to his mouth with a set of metal springs.
Dentures have, of course, come a long way since then. And new research promises access soon to something far more advanced than hippopotamus choppers — real human teeth, grown in laboratory dishes.
Scientists also hope that by locating the right biological triggers, people may one day be able to grow several sets of teeth instead of just two — much like the way sharks, rodents or stingrays grow several generations of teeth to replace worn out or rotted ones.
“Nature has developed over a long time certain tissues that have a particular function,” says Mary MacDougall, associate dean of the dental school at the University of Texas Health Science Center. “So there’s nothing like being able to use the real thing.”
Tooth Parts in a Petri Dish
MacDougall has managed to grow the real thing, or at least parts of it, in her laboratories at the University of Texas. She and her students first dissected tissues borrowed from extracted wisdom teeth. Then they added extra genes to the tissue cells that make up the tooth’s outer shell, enamel and its inner hard surface, dentin so the cells would continue to replicate in culture. After nurturing these cells in moist conditions, the team soon had human tooth parts growing in culture.
“We have little factories that make the natural enamel and dentin for us in a dish,” she says.
Unlike most bones in the human body, tooth enamel is made up of cells that die off as the tooth forms. That’s why when enamel tissue rots, dentists replace it with fillings. MacDougall says new filling materials such as amalgam and plastics are often tested first on lung cell tissues since these cells reproduce well in culture.
She hopes developers can soon test new filling materials in lab-grown tooth tissues. And if all goes according to plan, filling tests would become obsolete since dentists will be able to grow real tooth enamel fillings in the lab.
That prospect, MacDougall says, is at least a decade away. Even farther away — about 20 years — is the prospect of triggering cells still in the mouth to regrow teeth. To do that, scientists must first find the genes and proteins that regulate the tooth-growing process.
As Harvard University geneticist, Richard Maas points out, mice provide a great tool for finding those genes. Particularly, strains of mice in which a single gene has been deleted — known as knock-out mice — have proved fruitful for finding tooth-growing triggers.
“A lot of the knock out mice made turned out to have a tooth defect,” he says. “That discovery has been more or less accidental.”
Maas was able to confirm that a natural substance known as BMP4 helps spur the growth of teeth in mammals, by inserting it into the jaws of chick embryos. There are actually no such thing as hen’s teeth — but the chicks with BMP4 developed the beginning buds of teeth.
“Once upon a time, ancient birds did have teeth,” says Maas. “But at some point it seems the signal to grow them was interrupted.”