Though Ms. Wilson did not know it when her trouble started, this dispute is one of many taking place all over the country between nondentist teeth whiteners and state dental boards. This issue is itself part a much broader debate over the proper limits of occupational licensing and the amount of leeway that professional boards should be given to set up barriers of entry.

“Licensing is a labor market institution that’s been growing dramatically,” said Morris M. Kleiner, a professor at the Humphrey School of Public Affairs at the University of Minnesota, who has written books and papers on the subject. Five percent of United States workers had jobs that required licenses in the 1950s, he has found, and that has risen to around 30 percent now.

For Ms. Wilson, though, this is just about teeth.

“Teeth whitening is for everybody,” she said, describing it in the context of permanent makeup, microdermabrasion and various other procedures that perhaps explain why she does not look 71 years old.

Teeth whitening began to flourish in the 1990s, with dentists using forms of peroxide to essentially bleach the teeth (as opposed to removing stains, which is part of routine cleaning). The service generally costs around $300 or more, according to court documents; by 2006, a survey by the American Academy of Cosmetic Dentists found that dental practices were making an average of $25,000 a year from teeth whitening.

Later, whitening strips or kits — which often consist of peroxide gel, an application tray and in some cases a little LED light that activates the gel — began appearing online and in pharmacies, where they can be bought over the counter like cosmetics.