The family of a 2-year-old boy who died after receiving a routine crown dental procedure at an Arizona clinic says the staff made several negligent errors that could have led to the child’s death.

In Dec. 2017, Zion Gastelum’s mother, Veronica, brought her son to the Kool Smiles dental clinic in Yuma to treat his severe cavities. Zion was scheduled to have nine of his baby teeth treated, including root canals and crowns on six of the teeth. After the procedure, anesthesiologist Aaron Roberts, who was contracted by the clinic, told police the procedure had gone “well,” according to a police report obtained by ABC 15.

However, in a lawsuit, Zion’s family alleges the clinic made several missteps to ensure the safety of their son. The suit alleged X-rays or further investigative exams were not conducted to confirm that the nine procedures were necessary. Additionally, the family claimed a staff member allegedly muted the alarm on Zion’s heart monitor and that the oxygen tank he was hooked up to was empty.

“Once these invasive procedures were complete, Zion was extubated and taken to a separate room for recovery from general anesthesia. Despite the fact that Zion was not awake and had not regained the ability to breathe on his own, the Kool Smiles dentists chose to leave Zion alone in order to begin procedures on the next child-patient(s),” the lawsuit alleges.

While in recovery, Zion was given supplemental oxygen from a tank, but “the oxygen tank was empty or not operating properly.” Veronica Gastelum said she entered the room when she heard the heart monitor beeping and saw a staff member mute the alarm.

“Shortly thereafter, the alarm went off an additional three to four times – each time silenced by the Kool Smiles staff member – until the staff member finally removed the monitor from Zion and stated that the device does not work on children,” the lawsuit claims.

Once Gastelum noticed her son had no pulse, the staff began to react. Zion was rushed to Phoenix Children’s Hospital where he was diagnosed with brain damage caused by lack of oxygen. He died four days later.

A medical examiner later ruled that his cause of death was “undetermined.”

“This is a death that could have been prevented and should have been prevented,” Scott Eldredge, an attorney representing the family, told ABC 15. “Had proper procedures been followed, Zion would be with us today.”

An attorney for the anesthesiologist told the news outlet that it was “an isolated and unfortunate incident,” but that “there are a number of factors unknown to the press or public, but as a matter of policy, we cannot comment on pending or active litigation.”

Kool Smiles, a dental office chain that specializes in treating low-income families, has previously run into legal trouble for harmful practices. In January 2018, the U.S. Department of Justice settled a False Claims Lawsuit with the company resulting in a $23.9 million fine.