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There are companies that act as stem cell banks that will take your children's milk teeth in by post and process them and store them (hopefully where they will never be required).
They also process and store stem cells from umbilical cord/blood.
Google: stem cell bank
(I've kept most of my daughter's milk teeth just because that's where the "tooth fairy" dumps them after the requisite £1 or £2 has been extracted. I have no plans to actually send them to a stem cell bank though.)
Never thought I'd learn anything in this thread, except the comfort that comes with wealth obviously.
I'd also say that this information substantially raises the value of my kids teeth. Not good for the tooth fairy.