Should dentists alone be allowed to decide who whitens your teeth? That is the question in an antitrust case before the Supreme Court that could clarify whether antitrust laws apply to professional licensing bodies, which are often packed with people in the industry.

The case, North Carolina State Board of Dental Examiners v. Federal Trade Commission, involves the state board’s attempt to squelch competition and keep prices high by telling salons, spas and other businesses to stop offering teeth whitening services because they are not licensed dentists. The board consists mainly of dentists elected by their state-licensed colleagues. But no other body in North Carolina, including the courts or the State Legislature, had previously determined that only dentists could whiten teeth.

The F.T.C. challenged the board and told it to stop sending out cease-and-desist letters to teeth whitening businesses. The board appealed, arguing that as a state agency it had immunity from federal antitrust laws. The United States Court of Appeals for the Fourth Circuit, in Richmond, Va., ruled in favor of the F.T.C.

Many state governments give doctors, dentists, lawyers and other professionals limited authority to regulate the way their occupation is practiced. But the Supreme Court has ruled on other occasions that state officials must actively supervise those professional regulatory bodies if they are to be immune from antitrust law. In this case, the board’s cease-and-desist letters were not reviewed or approved by North Carolina.