For the first time, researchers have isolated human postnatal stem cells directly from the periodontal ligament, according to a study in the July 10 issue of The Lancet.
Senior author Dr. Songtao Shi said scientists have suspected since the 1970s that the periodontal ligament, or PDL, might contain its own stem cells. They have not, however, been able to prove this, and some wondered if stem cells could be extracted from such a small amount of tissue.
About two years ago, Dr. Shi and colleagues obtained PDL tissue from 25 newly extracted third molars. They then extracted, sorted and cultured the various cells from the tissue.
Researchers noticed numerous rapidly dividing cell colonies that had the general characteristics of stem cells. They confirmed their observation when they detected two proteins that are known to reside on the surface of mesenchymal stem cells, the general type of postnatal stem cell from which those in the PDL would be derived developmentally.
They also detected an unusually high level of a gene-activating protein that is specific to cells in tendons, which further suggested that PDL stem cells have been grown.
After further validation of their findings, researchers transplanted stem cells—each derived from a distinct colony cultured in the laboratory and loaded into a hydroxyapetite carrier—to determine if these stem cells could form PDL and cementum when transplanted into mice and rats.
Of the 13 transplants, eight produced a dense mixture of cementum and PDL, as well as fibrous structures similar to Sharpey’s fibers, which insert into both cementum and bone to hold teeth in place. The other five transplants showed no signs of differentiation.
Researchers are following up on this finding using larger animals. If successful, Dr. Shi said they would like to evaluate the cells’ regenerative ability in humans who have advanced periodontal disease. "From a clinical point of view, what’s nice is these stem cells are easily accessible," said Dr. Shi. "In theory, people could one day preserve, or bank, these stem cells when they have their wisdom teeth extracted, opening the door for biology-based regenerative treatment later in life of advanced periodontal disease."
