42 C.F.R. § 31.13
(e) Expenses for consultants or special services, or for dental treatment other than emergency measures to relieve pain, shall not be allowed except when authorized in advance by the headquarters of the Service or, in extraordinary cases, when subsequently approved by such headquarters upon receipt of report and satisfactory explanation as to the necessity and urgency therefor.
(Sec. 610(b), 58 Stat. 714 as amended; 33 U.S.C. 763c)