LIPUS

Low intensity pulsed ultrasound (LIPUS) is a medical technology.
Researchers at the University of Alberta have used LIPUS to gently massage teeth roots and jawbones to cause growth or regrowth, and have grown new teeth. As of June 2006, a large device has been licensed by the Food and Drug Administration (FDA) and Health Canada for use by dentists. A smaller device that fits on braces has also been developed. In order to regrow teeth, the tooth root must be massaged by the LIPUS device for 20 minutes each day for 4 months. It has been approved by both Canadian and American regulatory bodies and a market-ready model is currently being prepared. LIPUS is expected to be commercially available before the end of 2009.
See also:
http://www.sciencedaily.com/releases/2006/06/060628234304.htm
http://www.theregister.co.uk/2006/06/29/ultrasound_tooth_implant/