Kool Smiles in the largest dental chain serving kids on Medicaid, with about 2 million patients. But the chain has been criticized by regulators in three states for allegedly doing unnecessary procedures on children. The company denies this, saying it provides quality care to children in need.

Donna Balaski, who heads Connecticut’s Medicaid dental program, said X-rays from Kool Smiles in 2010 showed cases where dentists wanted to put stainless-steel crowns unnecessarily on tiny cavities. After difficult talks with Kool Smiles, Balaski said she’s now happier with their performance.

A Kool Smiles office in Virginia last year diagnosed Jacey Regan, then 4, with seven cavities, five needing stainless-steel crowns. Her father, Robert, took her to specialist in children’s dentistry. He said she didn’t need any of the crowns yet. Kool Smiles diagnosed Jacey as a high risk patient for cavities and said under those circumstances, crowns were appropriate treatment.

One of Kool Smiles’ most controversial practices is its dentists’ heavy use of stainless-steel crowns to restore decayed baby teeth. Medicaid pays far more for crowns than for fillings to treat cavities. The crowns are premade and cost dentists only a few dollars. The company says it uses fewer crown per patient than average.

Christina Bowne, who managed a Kool Smiles office in Portsmouth, Va., for three years, said the company’s system rewards dentists who bill as much as possible. The company disputes her account.

Kari Reyes was pleased with the Kool Smiles treatment she was getting for her 3-year-old daughter Marissa, until a new dentist there changed the treatment from fillings to crowns. Reyes agreed, but became upset when her daughter, strapped down in the chair, was screaming in pain. A new dentist said Marissa was treated too aggressively.

Republican Senator Charles Grassley of Iowa has had investigators looking at Kool Smiles and a few other corporate dental chains. “I’m finding in this investigation that there are people that know nothing about dentistry are saying you got to see so many people, you got to do so much work for each one, and in a sense, gaming the system,” he said.

Kool Smiles pays dentists 25 percent of what they bill, beyond a certain threshold. The contract includes language that to be eligible for a bonus, the office must meet quality standards.