VANCOUVER, Wash. -- A 4-year-old Vancouver boy has died after what seemed like a routine dentist visit last week.

Mykel Peterson was put under with anesthesia to fill a cavity, but never woke up. The dental office where it happened, Must Love Kids, was closed Monday. An employee who came to the door, told KGW it was out of support for employees and the boy's family after what happened Friday.

The Washington State Dept. of Health says it's now reviewing the case to decide if they'll open an investigation. The Clark County Medical Examiner says the cause of death is pending until toxicology results are finalized in 6-8 weeks.

Photos of Mykel Peterson show he had a contagious smile. Family members say he liked to play little jokes and was always laughing. He was a favorite at his Vancouver pre-school, and a whiz on his bike. One thing most kids like Mykel didn't like, is the dentist.

"He didn't want to go, he was saying no. He was crying, not hysterically just whining," said his mother Thmeka Curry.

But Must Love Kids Pediatric Dentistry on S.E. 117th Ave. in Vancouver always saved the day. It's a very popular office for kids and parents, with gleaming reviews on apps like Yelp.

4-year-old Mykel Peterson of Vancouver, Wash., died after dental surgery. Photos provided by family or by KGW of Must Love Kids dentistry office. March 2017

Their YouTube video shows why kids love it: games, toys, Netflix playing on tvs in the ceiling while kids are laying in the dentist chair. It's an instant distraction to nervous kids.

His mother says Mykel is on the autism spectrum. His speech and behavior had been making big strides this year. It's why he needed special attention at the dentist.

"He woulnd't keep his mouth open so they can actually see what's going on," Curry explained.

The website for Must Love Kids says they specialize in helping developmentally disabled kids, offering a board certified anesthesiologist MD.

Mykel had been slightly sedated before using a nitrous oxide mask, but Friday, his mother says Mykel got a shot of the common anesthesia drug Ketamine to put him totally under while the dentist looked at whether he needed fillings or a crown. The procedure went well, it's what happened afterward that's changed her life..

"The dentist was telling me everything she did with this teeth and she was going to check to see if he was awake yet," Curry said.

Minutes ticked by, and Curry says he was breathing. Then he wasn't. CPR started, 911 was called and Mykel was rushed to the hospital where he was pronounced dead.

4-year-old Mykel Peterson of Vancouver, Wash., died after dental surgery. Photos provided by family or by KGW of Must Love Kids dentistry office. March 2017

"Now I'm in this situation where I'm sitting here waiting to know what exactly his cause of death was," Curry said. "I never knew kids around the world are losing their lives because of being put to sleep by a dentist, until it happened to my son."

Just last year, two California children and a Texas girl also died while under dental anesthesia. Curry is begging parents to ask more questions.

"Make sure they clarify what's going on. If the doctors don't say anything, ask. Be the voice for your kids."

Must Love Kids released a statement to KGW:

Statement from Drs. Prashant and Monisha Gagneja and Dr. Chelsea Zamudio

March 13, 2017

"As dentists and staff devoted exclusively to the needs of children, all of us at Must Love Kids® Pediatric Dentistry are heartbroken and devastated by this event. We ask the community to join us in thoughts and prayers for the family.

As to the specifics, outside medical experts will review what happened, so it would be premature to comment. We can say that we have always been passionate and taken the utmost care of our patients and their families, and provide the highest standard of care in a safe environment. We will continue our devotion to providing the best care to our patients.

There are times when the use of general anesthesia is necessary to provide quality dental care for children. We have performed dentistry for pediatric patients under deep sedation and general anesthesia more than 1,900 times without incident in the last three and half years in Vancouver. We contract with an independent, highly qualified and experienced board-certified anesthesiologist for anesthesia services who follow strict protocols, including a pre-operative checkup and clearance by the child's primary physician prior to the procedure.

Must Love Kids® is a Vancouver pediatric dentistry clinic founded to provide individualized, high-quality, state-of-the-art pediatric dental care for children in a fun,friendly atmosphere. The clinic founders, Drs. Monisha and Prashant Gagneja, are board-certified pediatric dentists and between them have 28 years in the practice of pediatric dentistry. Dr. Chelsea Zamudio previously was the Chief Resident at the Westwood Pediatric Dentistry Residency Program, University of California, Los Angeles (UCLA)."