42 CFR §440.50

1. (a)“Physicians' services,” whether furnished in the office, the beneficiary's home, a hospital, a skilled nursing facility, or elsewhere, means services furnished by a physician—
   1. (1)Within the scope of practice of medicine or osteopathy as defined by State law; and
   2. (2)By or under the personal supervision of an individual licensed under State law to practice medicine or osteopathy.
2. (b)“Medical and surgical services of a dentist” means medical and surgical services furnished, on or after January 1, 1988, by a doctor of dental medicine or dental surgery if the services are services that—
   1. (1)If furnished by a physician, would be considered physician's services.
   2. (2)Under the law of the State where they are furnished, may be furnished either by a physician or by a doctor of dental medicine or dental surgery; and
   3. (3)Are furnished by a doctor of dental medicine or dental surgery who is authorized to furnish those services in the State in which he or she furnished the services.