What was supposed to be a routine dental visit turned into a tragedy for 9-year-old Silvanna Moreno who died on March 18, 2025, a few hours after receiving dental procedure at Dreamtime Dentistry in Vista, California.

Now, more than two months after her tragic passing, the San Diego County Medical Examiner’s Office ruled her death an accident.

The cause of death was listed as “methemoglobinemia in the setting of recent nitrous oxide administration.”

MetHb happens when haemoglobin is impacted by nitrous oxide, which lowers oxygen transport to tissues and results in hypoxia, as explained by the Cleveland Clinic.

It is an uncommon blood condition that affects the way red blood cells carry oxygen throughout the body. At some people, it manifests with blue or purple lips, skin, or nails, while at others, it is asymptomatic.

According to People, Silvanna had a fever and was given children’s Tylenol a day before the three-hour-long procedure.

The dentist’s office that treated the girl said she was a new patient referred to them for a root canal on a molar.

During the dental procedure in which the 9-year-old died, some baby teeth, as well as one permanent decayed tooth, were extracted.

According to NBC News, Dr. Ryan Watkins, the office’s trained anesthesiologist, said in a statement that “Silvanna was a healthy 9-year-old with a history of regular medical checkups.” He added that she underwent the office’s standard preoperative evaluation and was “an appropriate candidate for outpatient general anesthesia”

The Medical Examiner’s summary report stated that the girl was moved to a “recovery room” following the procedure. It added that Silvanna’s mother told investigators her daughter was “out of it while intermittently opening her eyes and incomprehensibly mumbling.”

On the way home, as well as when they arrived home, she was sleeping. Around half and hour later, her breathing slowed. They tried to wake her up, but when they failed to do so, they called 911.

Silvanna was rushed to the hospital, where she was pronounced dead.

“We are profoundly saddened by the tragic loss of Silvanna Moreno, and our hearts continue to go out to her family during this incredibly difficult time,” Watkins said.

In 2016, Watkins was investigated for the death of a 54-year-old man who nearly died while under general anaesthesia. It was determined at the time by the Dental Board of California that one of the drugs he received shouldn’t have been given to him in the first place because it caused his heart to stop.

Watkins was put on probation from 2020 to 2023, according to a decision order.