Fully formed adult teeth do indeed provide a rich source of cells for a variety of graft/tissue engineering procedures including a variety of stem cells from cementum and PDL, as well as pulp cells and some from developing stages of teeth, too. As regards autogenous bone graft, yes the tooth enamel is essentially hydroxyapatite (HAp) and the same chemical composition as that of bone. However, please note, the crystallinity and arrangement/packing of the HAp crystals is different in a tooth compared to bone HAp, and this may dictate optimal use of such a graft.