As a therapist and researcher on dating, Scott Sibley is used to talking about the nature of interpersonal relationships and appearances.

So when he recently started to feel self-conscious about the widening gap between his front teeth, the Northern Illinois University professor of family sciences and human development decided it was time for the doctor to become the patient.

Sibley visited an orthodontist earlier this year and started a 20-week treatment plan using Invisalign, a system of teeth-straightening, removable, clear-plastic aligners made by Align Technology that serve as an alternative to braces.

“The gap just really started bothering me quite a bit,” Sibley said. “For me it was a lot about personal confidence. I just felt better about myself knowing I could have straight teeth again.”

Now, he does. And there are many more like him who are poised to do the same thing.

The market for clear teeth aligners is booming, allowing millions of Americans who can’t afford braces or dread the metal-wire experience to straighten their teeth for the first time. The number of Invisalign treatments alone has tripled over the last five years, with an expected 1.3 million people worldwide starting the treatment this year.

The rise of Invisalign and the emergence of competitor SmileDirectClub have spawned a surging industry that’s competing with traditional braces offered by orthodontists. Align estimated in a public filing that 300 million people worldwide “could benefit from straightening their teeth but are unlikely to seek treatment through a doctor’s office.”

Prices range from about $2,000 for mild-to-moderate teeth straightening from start-ups like SmileDirectClub and Candid, to an average of $5,500 for Invisalign, which can handle more crooked cases. Invisalign also offers a $2,500 option for correcting simple cases.

Braces average $5,000 to $6,000, according to life-sciences industry analysts at investment bank and financial services company Jefferies.

The opportunity for people is obvious: Straight teeth can help your personal confidence, your health, your relationships and even your job prospects.

“I think it makes a person more attractive” to mates and employers, said Sibley. “There’s something to be said for a person’s smile — no doubt about that.”

But as change reverberates through the lucrative oral-health industry, the intensifying competition has triggered a flurry of lawsuits and dental board complaints alleging health-law violations.

And proponents of traditional braces have voiced concerns about the do-it-yourself treatment plan of SmileDirectClub and other start-ups that enable patients to get straighter teeth without visiting an orthodontist or dentist.

Taken together, the developments reflect a wholesale realignment of an industry that avoided significant disruption for decades.

“We’re in the first inning of the aligner boom,” said Nick Greenfield, CEO of Candid Co., a New York-based start-up that recently secured $25 million in venture capital to expand its teeth-aligner business.

How it works

The game has been dominated in the early going by Invisalign, which operated for several years with negligible competition.

Founded in 1997, the company eventually perfected a mouth-scanning system and software that collectively create a digital 3D model of a patient’s mouth.

Here's how Invisalign works:

1. Patients get their mouths scanned in person. Using that data, Invisalign makes clear aligners that progressively move teeth into place.

2. Invisalign-trained dentists or orthodontists attach temporary tooth-colored brackets to the patient’s teeth, if necessary, enabling the aligners to stay in place and do their job.

3. Patients must visit a dentist or orthodontist about once a month or so for regular checkups to ensure the treatment is progressing as expected.

4. After the treatment is completed, the brackets, if used, are taken off.

5. Altogether, the process takes about 12 to 18 months. Patients are told to wear their retainers for a while during the day and permanently overnight going forward.

Aligners tend to appeal to patients who want straight teeth but fear braces or don’t want others to notice them.

Braces have the advantage of being able to fix the worst cases, but they can’t be removed until treatment is finished. By contrast, patients can take aligners out for any reason, including eating, drinking and romantic encounters, though they’re supposed to keep them in for at least 22 hours a day to maximize effectiveness.

“People are demanding more and more the convenience and the opportunity that plastic offers versus wires and brackets,” Align Technology CEO Joseph Hogan said.

About 12 million people globally begin orthodontic treatment yearly, including four million in the U.S., and some 90 percent of them get braces, according to Align.

Even with aligners accounting for a fraction of the market, Align has ballooned into a publicly traded company worth nearly $16 billion on the stock market as of Thursday. Invisalign has already treated more than five million patients.

But the company’s stock has fallen by about half over the last several months following a surge of competition, the expiration of key patents on its technology and concerns among investors that prices could fall.

The company’s biggest threat is SmileDirectClub, which has become a multibillion-dollar force since its founding in 2014.

While the two companies are competitors, their business approach differs. Align deals directly with orthodontists and dentists who then sell the Invisalign service to their patients. SmileDirectClub sells its services directly to patients.

SmileDirectClub’s approach has gained traction. SmileDirectClub allows customers to get treatment without ever leaving their homes, instead of requiring patients to get their mouths scanned in person and make office visits for checkups every few weeks. Here's how it works:

1. After customers sign up online, the company sends them an at-home impression kit.

2. At-home customers receive detailed instructions and videos on how to take photos of their mouths, sink their teeth into putty that quickly hardens and send the material back to SmileDirectClub.

3. One of SmileDirectClub’s more than 225 contracted orthodontists or dentists reviews each case and approves the treatment plan.

4. Patients receive a series of aligners to use over the course of the following months until their teeth are straight. They can send photos to SmileDirectClub for checkups.

5. After the treatment is completed, which averages six months, patients are told to wear a retainer during the day for two weeks and permanently at night.

Co-founded by Alex Fenkell and Jordan Katzman, who met as kids with braces at summer camp, SmileDirectClub is now valued at more than $3 billion, based on an investment of more than $380 million in October.

The company says it’s providing a chance for many Americans, including low-income people and residents in rural areas without nearby orthodontists, to get straight teeth for the first time.

“We eliminate those costly and timely in-office visits and pass on those savings to our customers,” Fenkell said.

The company has already treated more than 300,000 patients and opened more than 150 stores, where customers can get their mouths scanned instead of starting with the at-home impression kit.

“We’re selling confidence,” said Fenkell.

Orthodontics industry raises concerns

But not everyone is on board.

SmileDirectClub’s model has drawn criticism from the orthodontics industry. The American Association of Orthodontists, or AAO, has filed complaints against SmileDirectClub in at least 36 states, saying that the company’s do-it-yourself model violates dental-practice statutes.

The interest group has also issued a “consumer warning” about SmileDirectClub and other mail-order orthodontics businesses.

“Orthodontics is the movement of biological material, and it’s best done under the supervision of a licensed orthodontist,” said Sean Murphy, AAO’s general counsel. “If not done correctly, (it) can lead to potentially irreversible and expensive damage, such as tooth and gum loss, changed bites and other issues.”

Murphy said the AAO has not taken action against Align because Invisalign’s on-site supervision is allowable under state laws.

At least two states have already taken some form of action against SmileDirectClub. Georgia recently issued a regulation requiring digital scans to be taken with a licensed dentist on site, while Alabama issued a cease-and-desist order after ordering the company not to practice there.

“It’s up for the dental boards to determine what is the appropriate remedy to provide, but we just want the patient’s health and safety to be protected — and to get that done we believe the dental laws have to be followed,” Murphy said.

SmileDirectClub has responded with lawsuits against the dental boards in Georgia and Alabama. Fenkell said SmileDirectClub’s results have demonstrated safety and reliable performance. The company continues to operate in those states.

“Whenever you disrupt an industry there’s going to be inherent friction, there’s going to be naysayers,” Fenkell said.

Jeffrey Sulitzer, SmileDirectClub’s chief clinical officer, said orthodontists are trying to preserve their “Mercedes pricing” on braces.

Sulitzer defended the company’s safety, saying doctors remotely review photos of patients' mouths during the teeth-correcting process to ensure everything is progressing correctly. If a patient’s teeth are not responding as expected, SmileDirectClub requests that customers take a new impression and then sends new sets of aligners, he said.

“The doctor is the one who’s managing the case from the very beginning to the very end,” Sulitzer said. “These doctors that are affiliated with us — most of them have a bricks-and-mortar practice. And they treat their patients within the same standards of care that they treat their bricks-and-mortar patients. And they’re also regulated by the dental boards.”

He said SmileDirectClub would be vindicated in its fight against the AAO.

Murphy said the AAO’s action “isn’t a protectionism-type exercise” and that the group has “a stable membership” of doctors.

Brandon Couillard, an equity analyst for Jefferies who tracks the teeth aligner industry, said the AAO’s action against SmileDirectClub is “a natural response” by “a lobbying organization that is threatened, in the sense that this takes the orthodontist’s role out of the equation in many regards.”

But he said it’s unlikely that SmileDirectClub can be stopped given the growing appeal of aligners among consumers.

“I think the genie is out of the bottle now,” he said.

What’s more, accusations of treatments gone wrong seem to have thin roots, Couillard said.

“I’m sure there are cases where a consumer didn’t get the outcome they thought they would,” he said. “But I haven’t seen any instances where a consumer has been harmed.”

Cutthroat competition

The aligner companies say they’re all benefiting from a rising tide that’s lifting the entire industry. But that hasn’t stopped them from airing accusations of competitive fouls and filing a flurry of lawsuits against each other.

The wide range of legal fights reflects the cutthroat nature of the business. It also makes for an awkward state of affairs, considering that some of the companies suing each other do business together.

Align, for example, owned 19 percent of SmileDirectClub as of earlier this year and supplies plastic aligners to SmileDirectClub. But now SmileDirectClub is suing Align for opening several Invisalign Experience stores, saying those locations infringe on its competitive turf. The Invisalign Experience stores offer a free digital scan and connect customers with an orthodontist or dentist in their area for treatment.

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“The idea behind our partnership is that we stay in our lanes," Fenkell said.

Align said it hasn’t violated its arrangement with SmileDirectClub. When customers visit its new stores, it ultimately refers them to a dentist or orthodontist for Invisalign treatment.

At least for now.

Couillard said it’s “possible in the long arc” that Invisalign could be sold directly to consumers, as well. That would pose a serious threat to SmileDirectClub.

Despite their legal dispute, SmileDirectClub’s rise has “very likely had a positive halo effect for Align,” Couillard said.

Start-ups enter the scene

As existing companies jockey for customers, more competition is developing on the horizon as investors pile money into start-ups.

Candid CEO Greenfield said his start-up would open up to 100 stores throughout the U.S. by the end of 2019.

Candid Studios locations offer patients the chance to get scanned in person, like Invisalign, and then get mailed their aligners, like SmileDirectClub. The company also offers do-it-yourself at-home impression kits for about $2,000, with treatment plans remotely prescribed only by orthodontists.

“If you’re getting knee surgery, you don’t want an emergency-room doctor doing knee surgery for you. You want an orthopedist doing it. The same thing applies when having orthodontists,” Greenfield said. “They’re specialists who spent extra time in grad school and decades actually knowing how teeth are supposed to move. You can see the difference in the outcomes for our patients.”

Still, the AAO’s consumer-alert also applies to Candid under the premise that patients always need in-person oversight to ensure their health and positive outcomes.

Greenfield argued that so-called teledentistry is especially critical because it extends care to rural areas and lower-income customers who can’t afford braces or Invisalign.

About 60 percent of American counties don’t have an orthodontist, “which is just staggering,” Greenfield said. “Consumers are really the winner here.”

The AAO’s Murphy said the group “is definitely supporting increased access to dental care. But of course the increased access to care needs to be in the best interests of patients’ health and safety and comply with the states’ dental laws.”

Sibley, the Northern Illinois therapist who got Invisalign treatment, said he’s happy he had an orthodontist overseeing his Invisalign. And overall he’s grateful for the clear-aligner boom.

“I imagine more and more people will be doing this as they recognize that it just wasn’t that invasive,” he said. “It was something I had to think about every day. But it just wasn’t that big of a deal.”

Common questions about clear-plastic teeth aligners:

What are they? Removable clear plastic aligners that serve as an alternative to braces.

Do they hurt? Some discomfort is normal when starting new aligners.

Do they affect your speaking? A temporary, minor lisp is possible, though it usually goes away quickly.

What are the most common brands? Invisalign and SmileDirectClub.

How much do they cost? Less than $2,000 for mild cases through SmileDirectClub; an average of $5,500 for more complex cases through Invisalign.

Can they be removed? Yes, for eating, drinking or romantic encounters.

How often must they stay in? Typically about 22 hours a day.

How long does it take? Several months for mild cases to more than a year for complex cases.

Follow USA TODAY reporter Nathan Bomey on Twitter @NathanBomey.