What was meant to be a routine dental visit turned tragic for 9-year-old Silvanna Moreno, who died on March 18, 2025, just hours after undergoing a dental procedure at Dreamtime Dentistry in Vista, California.

More than two months later, the San Diego County Medical Examiner ruled her death an accident, caused by “methemoglobinemia in the setting of recent nitrous oxide administration.” This rare condition interferes with hemoglobin’s ability to carry oxygen, leading to potentially fatal hypoxia.

Silvanna had been given children’s Tylenol the day before the three-hour dental procedure. During the visit, she had a root canal and several tooth extractions, including one permanent decayed tooth.

Dreamtime Dentistry stated that Silvanna was a new patient referred for the treatment. Dr. Ryan Watkins, the office’s anesthesiologist, said she had a history of regular medical checkups and was considered an appropriate candidate for outpatient general anesthesia.

After the procedure, Silvanna was moved to a recovery room. Her mother told investigators she was “out of it,” occasionally opening her eyes and mumbling. On the way home and after arriving, she continued to sleep.

About 30 minutes later, her breathing slowed. When her family couldn’t wake her, 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,” said Dr. Watkins in a statement.

Her death highlights the rare but serious risks associated with sedation in pediatric dentistry.