It's perfectly normal to keep the first milk tooth your child loses somewhere safe for posterity. Maybe it gets squirrelled away in the same (slightly gross but sentimental) keepsake box as their umbilical cord stump and first lock of hair. While keeping more than one milk tooth might seem a bit morbid, it could actually one day save your child's life. It's all to do with the stem cells found in the bone marrow. Baby teeth are PACKED with bone marrow, which is good news according to the United States National Centre for Biotechnology Information because these precious stem cells can be used to treat cancer and diabetes, produce new eye tissue and growing bones. Extracting stem cells through bone marrow can be a very painful procedure for patients, but with baby teeth, the bone marrow can be accessed a lot more easily. What's more, stem cells can still be used even if the tooth is 10 years old. Another benefit of stem cells harvested from baby teeth is that baby teeth aren't that exposed to environmental wear and tear, meaning the cells are in good condition still. Stem cells derived from baby teeth can also be handy for fixing dental injuries such as dead teeth, reports sciencealert.com.So you may have to ask the Tooth Fairy for those gnashers back...