Shi, a pediatric dentist by training, says it all started when his daughter, Julia, lost her first tooth. When holding the tiny incisor in his hand, Shi suddenly spied a speck of scarlet tissue nestled deep inside. He thought it might be pulp tissue, which is choked with blood vessels and nerves that keep the bone healthy. In adults, the pulp is also where stem cells are known to hide. So when Julia´s next tooth popped out, Shi hustled it to his lab, where a closer look revealed several stem cells amid the tissue.