Johannah Lancaster took her 3-year-old son to Dental Express for his first checkup, expecting a routine cleaning.

She never imagined the treatment plan the Niles, Ohio, dentist would come up with after he peeked into Gregory’s mouth for what seemed like only two or three minutes.

Michael Griesmer said the preschooler needed root canals – seven of them. Stunned, Lancaster asked why he had not even taken X-rays. Griesmer told her they weren't necessary.

“I figured he is a professional so I trusted him,” she recalls. “If I knew then what I know now, I would have never gone through with any of it.”

Two weeks later, in May 2013, the dentist put Gregory under and drilled his teeth. The Medicaid bill came to $1,273 – compared to the $61 that Medicaid would have paid for a checkup and cleaning.

What Lancaster didn’t know then: Dental Express was part of North American Dental Group, a chain backed by private-equity investors. At least a year earlier, the company had told dentists like Griesmer to meet aggressive revenue targets or risk being kicked out of the chain. Those targets ratcheted up pressure to find problems that might not even exist.

Johannah Lancaster's son, Gregory, now 9, received seven root canals at a dental clinic when he was 3. The dentist never took X-rays and Gregory later had to have four of the teeth pulled. Jeff Swensen, for USA TODAY

“The 3-year-old boy was subjected to massive overtreatment,” said Nicholas Dello Russo, a dentist and instructor at Harvard University’s dental school who reviewed Gregory’s records. “This is child abuse.”

North American Dental Group follows a new trend of dental offices bought by private-equity investors and turned into revenue-generating machines. The chain started in Ohio and soon became among the fastest expanding. It now has more than 200 offices in 13 states east of the Rockies, handling a million patient visits a year. Late last year it was bought by a Swiss firm that also owns hundreds of dental offices in Europe.

While any dentist might be tempted to find ways to increase profit, private-equity firms often saddle their companies with heavy debt at junk-bond-caliber interest rates. That may leave patients vulnerable, critics warn.

North American Dental Group has become a lightning rod for complaints in recent years, especially from former dentists and employees who say revenue pressures went far beyond what is typical in the industry.

USA TODAY and the investigative unit at Newsy, owned by The E. W. Scripps Company, spent more than a year examining the dental chain. Reporters interviewed dozens of its former dentists, employees and patients and reviewed thousands of pages of documents from courts, dental boards, patient records, social media reviews and other sources.

The investigation found that the intense pressure on North American Dental’s offices to meet daily revenue targets led to allegations of overtreatment. Patients complained they were diagnosed with a mouthful of cavities only to later discover nothing was wrong with their teeth. Employees said they felt uncomfortable with what they witnessed.

“I have watched them drilling perfectly healthy teeth multiple times a day every day,” dental assistant Ashley Hughes said in an interview. She worked for two years at a North American Dental office in Austintown, Ohio, not far from where Gregory was treated.

The financial squeeze was part of a daily companywide ritual known as the “morning huddle.” Staff said they met before the doors opened to discuss how to fill gaps between that day's targets and scheduled treatments.

North American Dental pits office against office and dentist against dentist by sending out monthly tables ranking dentists and hygienists by who’s making the most money per appointment. Offices failing to hit their goals are colored in red – and told to step it up.

“Congrats to teams Alpine, Deerfoot and Life Smiles for starting the month out on a high note, exceeding their budget,” one regional manager wrote in a July email to 11 Indiana offices. “Everyone else has a deficit to overcome.”

Nicky Demecs' Facebook review of Corner Dental Courtesy of Nicky Demecs

USA TODAY and Newsy interviewed 20 patients who sought second opinions after being told at a North American Dental office that they needed extensive dental work. In each case they said the second dentist prescribed little to no dental work.

A dentist at Refresh Dental in Kent, Ohio, told first grade teacher Jennica Watson that she had seven cavities. Watson says she brushes twice a day and has checkups every six months. She went to another dentist, who said she had no cavities at all.

Twenty‑seven‑year‑old Alex Miller, who installs countertops, switched to a new dentist at Corner Dental in Maumee, Ohio, who told him that he had nine cavities. Suspicious, Miller went back to his family dentist, who told him he had none.

Gregory, at 3, when his root canals became infected. Courtesy of Johannah Lancaster

Nicky Demecs went to Corner Dental in Oregon, Ohio, and was told she had five cavities on one side of her mouth and three on the other. She had half the work done, then decided to get a second opinion: no cavities.

Patients had no way of knowing that their dental office was managed by a company beholden to Wall Street investors or that their dentists and hygienists were expected to meet revenue goals. As North American Dental snapped up offices, it often retained their original names.

Private dental chains receive virtually no oversight. These companies don’t have to file financial statements with the Securities and Exchange Commission. And state dental boards tend to only regulate dentists, not the companies. Even then, USA TODAY/Newsy found that dental boards rarely act on complaints.

In 3-year-old Gregory’s case, the Ohio state board did review the case. It suspended Griesmer's license more than a year later, board records show, only after Griesmer continued to treat other children without providing X-rays or adequate records to the board while under its supervision.

Gregory continued to have problems after the root canals, according to his mother and records from a malpractice lawsuit. While he was recovering from general anesthesia, one of his seven crowns fell off. Lancaster said she told the assistant, who came back with a message from Griesmer: He had used off-the-shelf crowns that “were the smallest ones made and they were still too big for Gregory and that it’s fine.”

But it wasn’t fine. More crowns came off over time and eventually Gregory’s right cheek swelled so much it looked like it might pop. Lancaster rushed him to an emergency room, where they drained pus. Later, a dental clinic pulled four of the teeth Griesmer had treated.

Gregory faced more surgeries to fix the damage, according to the family’s malpractice lawsuit. Those medical bills came to $23,000.

Last week, Griesmer told USA TODAY that he figured out that Gregory needed root canals – called pulpotomies when done on baby teeth – “just by sight.” He said he never took X-rays on 3-year-olds because they won’t sit still for them.