I'm also trying to figure out how to regrow teeth.
I came across some articles on how ultrasound (LIPUS) has helped to regrow entire teeth.
I've also seen people talk about using comfrey root.
Other ideas I've come across to help teeth in general are doing oil pulling, rinsing with natural Sea Salt and brushing with a toothpowder like Bentonite clay in order to help remineralize teeth.
I haven't tried comfrey or LIPUS. I just got a Bentonite clay based tooth powder, so it's too soon to tell what it will do.