Orthodontists and a customer launched a class action lawsuit against SmileDirectClub, accusing the company of fraud and false advertising just days after the Nashville-based startup's disappointing opening on the stock market.

In the lawsuit, filed with the federal court in Nashville, the plaintiffs call SmileDirectClub "a company under siege," citing complaints from the American Association of Orthodontists and customers.

SmileDirectClub customers can either use at-home molds or visit its retail shops to be fitted for molds to straighten their teeth. The company says it partners with dentists and orthodontists to oversee some of the treatments, a claim the lawsuit contests.

The suit says SmileDirectClub has violated laws regulating interstate commerce and consumer protections.

Three named plaintiffs are orthodontists in New York, Texas and Florida. The suit said they had "suffered an ascertainable loss of money or property" because of the company's actions.

A fourth plaintiff, a customer from Michigan, claimed her teeth were worse after using SmileDirectClub.

The plaintiffs are represented by Ed Yarbrough, a former U.S. attorney who now works at Bone, McAllester & Norton in Nashville.

The lawsuit further states that the company has responded to criticism with "a deliberate, intentional, and well-lawyered campaign to stifle any legitimate, publicly-stated concerns or criticisms of its product and/or business practices."

A company spokesperson declined to comment on the litigation. But the company previously hit back at a complaint filed with the U.S. Food and Drug Administration earlier this year by saying that, as the company amassed success, "organized dentistry has been ratcheting up its attempts to block competition."

SmileDirectClub went public earlier this month and has seen stock prices slump.

More than 58 million SDC shares were offered at a starting price of $23 each on Sept. 12. On Wednesday, share prices stood at $14.50.

SmileDirectClub recently announced a $217 million expansion of its Nashville offices downtown and in Antioch. The company said it would hire 2,010 new employees through 2024.

Reach Adam Tamburin at 615-726-5986 and atamburin@tennessean.com. Follow him on Twitter @tamburintweets.