Waitress Aimee Gharis faces the public constantly, but she used to be less than confident about her smile.

So when a local hair salon in Hamden, Conn., began offering teeth whitening for $99—far less than dentists charge—she bit.

"I didn't want to look like a crazy person with super white teeth you can see in the dark, but I wanted to look like I don't smoke, or drink coffee or red wine," says Ms. Gharis, who was thrilled with the results.

But not everyone is so chipper. Dentists are battling with spas, tanning salons and other nondental peddlers of pearly whites from North Carolina to New Jersey and, now, Connecticut over who should be permitted to meet the needs of a nation clamoring for an anchorman's smile.

Four out of five dentists, it seems, believe they should handle teeth whitening. But nondentists argue that the tooth doctors are just trying to protect their turf. As relations between the two sides have decayed, some Connecticut "teeth-whitening entrepreneurs" have begun a legal campaign to overturn a rule passed by the state's dental commission in June that bars nondentists from offering the service.

A teeth-whitening treatment by iSmile in Santa Ana, Calif. The Orange County Register/Zuma Press)

Dingy teeth were once relatively common. But after a 1989 scientific article touted the use of low levels of hydrogen peroxide, pressed against teeth, to improve smiles, companies began producing whitening products and dentists began hawking them.

Entrepreneurs jumped in quickly. The Food and Drug Administration classifies teeth-whitening products as cosmetics, and drugstores were soon selling strips that consumers could paste on at night while watching TV. Promising a faster fix, dentists, salons and mall kiosks began offering on-site treatments. Those customers typically bite down on a tray of goopy whitening agent and sit in front of LED lights that are said to enhance the transformation process.

Dentists generally charge between $300 and $700 for a whitening session, which isn't normally covered by insurance, while nondentists charge between $100 and $150, according to the Federal Trade Commission.

In Connecticut, the teeth gnashing began in June. That's when the Connecticut State Dental Commission, which then included seven dental professionals and one member of the public, passed "Declaratory Ruling: Teeth Whitening." Under the measure, only licensed dentists would be able to offer on-site teeth whitening, and in Connecticut, violators of state dental laws can get jail time.

The ruling wasn't prompted by any "specific reports of harm," but "we want to make sure that whatever is applied is applied safely," says Jeanne Strathearn, the board's chairman and a dentist who offers whitening. Teeth whitening can cause gum or tooth sensitivity, she says. In addition, tooth discoloration can be caused by underlying medical conditions that dentists are better able to spot.

But the Institute for Justice, an Arlington, Va., libertarian public-interest law firm, is representing nondental teeth whiteners in Connecticut. Paul Sherman, an attorney with the group, argues that the dentists are "using government power to stifle honest competition."

Lisa Martinez, a 29-year-old mother of two, opened her business, CT White Smile, in the Crystal Mall in Waterford, Conn., in 2008 but shut it in June after the dental board's ruling. "I don't think it's fair at all," she says. "I feel like everyone is an adult and can make a conscious decision after reading over risks involved."

Dentists in North Carolina and New Jersey have also tried to ban nondental whitening. In North Carolina, the state's dental board accused nondentists of engaging in unlicensed stain removal. The board dispatched a camera-toting investigator and sent out a flurry of cease-and-desist orders, scaring off proprietors like Whitening on Wheels and SheShe Studio, according to the board's "closed investigative files," which were submitted to the FTC after the agency sued the dental board last year.

In July, the FTC ruled that the dental board engaged in "anticompetitive conduct" and ordered it to revoke its orders to nondentists.

The dental board is appealing the ruling, says Noel Allen, the dental board's attorney. He argues that states' rights are at issue, specifically "whether states can continue to protect their citizens" through licensing boards.

Meanwhile, in New Jersey, whitening woes have led to "trying times" for tanning salons, says James Oliver, the chief executive of the Beach Bum Tanning & Airbrush chain, which offers $69 teeth-whitening sessions and features its most famous customer, "Jersey Shore" star Snooki, in a TV commercial.

The New Jersey Dental Association sued Beach Bum in a New Jersey superior court last year, alleging unfair competition and accusing the tanning chain of removing stains, which the association said amounted to practicing dentistry illegally.

Mr. Oliver said his stores merely hand customers a whitening tray. "We don't even put our hands in people's mouths," he said.

In April, the court ruled for Beach Bum. The association is appealing.

Still, dentists have been able to prevail in some areas. Alabama's supreme court blocked a hair salon from selling a teeth-whitening product in 2009, ruling that because the gel was applied in the store it constituted dentistry.

Write to Jennifer Levitz at jennifer.levitz@wsj.com