It was just before 1 p.m. on a September afternoon when Ramandeep Singh watched his five-year-old daughter whisked away in an ambulance from the dental office where she had received general anesthesia.

When she arrived at the Stollery Children's Hospital last year, Amber Athwal was immediately put on life support. She suffered a permanent brain injury, due to a lack of oxygen to her brain.

That same afternoon, the dentist who treated her accepted more patients and administered more anesthesia at his downtown office.

Dr. William Mather — charged with five counts of unprofessional conduct by the Alberta Dental Association and College — continued to treat and sedate patients for two more days.

Those facts were revealed Monday at a hearing tribunal into Mather's conduct.

As the hearing opened, the tribunal was told that Mather retired from his dental practice two weeks ago.

Singh said he was shocked when he heard about the dentist's actions on the day his daughter was hospitalized.

"I have no words," he said outside the hearing, being conducted by the ADAC.

"If his hands were not shivering when he went through this incident and still he was working on a patient? I can't believe it."

Four-year-old Amber Athwal in early 2016. (Ramandeep Singh) The 68-year-old dentist never held a meeting with his staff to discuss what happened to Amber. And the hearing was told that he didn't talk to his professional association about the medical emergency that unfolded in his office until representatives from ADAC contacted him two days later.

Father told 'she's fine'

In the hearing room, Singh testified that he had taken Amber to the office on Sept. 7, 2016, thinking they were there for a consultation. But Mather reportedly told him there had been a cancellation and he could treat Amber that day.

"I held Amber's hand," Singh told the hearing. "They put on the mask and turned on the gas. She started crying, screaming. With three deep breaths, Amber had fallen asleep."

Singh was asked to leave the room while the dental team did its work. About an hour later, the father saw staff running from the hallway to the area where his daughter was being treated.

Singh said Mather took him to the lunch room and asked him to sit down.

"He said that Amber got complications with her breathing during the procedure and paramedics were called, and they are taking care of Amber right now and they may take her to the hospital," Singh testified. "But she's fine now."

One year later, Amber cannot walk or say more than one or two words. She spent months at the Glenrose Hospital.

Singh told the tribunal that a medical team cut off his child's clothes and put her on life support. He said he was told that Amber, "won't be able to speak, listen. She won't be able to do anything in her life."

It took almost three weeks before Amber could open her eyes. She screamed during that time, and clenched her teeth so hard that she broke two teeth.

Amber Athwal sits in a chair in her home as her father encourages her to repeat the names of colours on a toy. (Travis McEwan/CBC) The 31-year-old father wept while recalling the events of that day.

Dentist now retired

Amber was wheeled into the hearing room on Monday morning by her mother. She stayed long enough for the tribunal members and Mather to see her.

Her father later said he thought it was important for people to witness first-hand what had happened to the little girl.

"We wanted to show everyone how our daughter was earlier and how she is now. We want to bring this open."

On Monday, Mather pleaded guilty to three of five charges and made several admissions:

He admitted he did not report the incident involving Amber to the dental association within one day, as required by the profession. He only spoke to the regulating body when representatives called him, two days later.

He admitted he continued to see and sedate patients, both children and adults, on the same day after he treated Amber, and for the next two days, until the dental association contacted him.

He admitted he over-billed three patients for anesthesia procedures around the time that Amber was treated and failed to create or maintain complete patient records.

Mather has also admitted he failed to have properly sterilized equipment.

This sign on the entrance to Dr. William Mather's office in October 2016 identified him as a dental surgeon and anaesthesiologist. The Alberta Dental Association and College listed Mather as a general dentist. (Janice Johnston/CBC News ) Mather is also accused of failing to provide proper care to the little girl when she stopped breathing, including failing to call 911 immediately, inadequate resuscitation efforts, and failing to immediately access a crash cart.

He is also accused of representing himself as an anesthesiology specialist when he was, in fact, a general dentist.

It is unclear what sanctions Mather may face if found guilty of more charges.

According to previously published decisions in other hearings, dentists have been suspended, ordered to take additional courses, and to pay the cost of the hearing and investigation into their cases.

The hearing is being held before a panel of four people, including three dentists and one member of the public.