Most of what dentists are permitted and not permitted to do is codified
in the state dental practice act.
    Using restorative materials is a professional choice; a dentist is free
to accept or reject a material or technique or procedure as their
professional judgment dictates.  They are of course responsible for the
results of their treatment decisions.  Generally they may NOT do a
dental procedure with the express intent of curing a medical condition
outside the scope of dentistry.  I'm sure it would be OK on prescription
of a licensed physician.  There is in fact a long history of this.  Back
in the day dentists extracted the teeth of patients scheduled to undergo
radiotherapy for head/neck tumors--something that had to be medically
justifiable.  Dentists work closely with physicians all the time.  The
problem is making treatment decisions unilaterally without medical input.

Steve

As an aside, I found this book a very interesting read:

http://www.amazon.com/Spin-Doctors-Chiropractic-Industry-Examination/dp/155002406X

John