My grandson has ha a baby tooth pulled by a pediatric dentist. His office is able to pull teeth in the office. My grandson has ADHD and Aspergers. He couldn't sit still. This dentist used gas for anesthesia. It's much easier on the body than general anesthesia used at a hospital. My grandson was awake and mostly alert immediately after the procedure which was done in the length of time of a regular appointment. He was a bit groggy for an hour or so. He was around the same age as your son.
A granddaughter had 2 or 3 baby teeth pulled by a different,preferred provider, dentist. It was done in an operating room with general anesthesia. She then had to go to recovery for 3 or maybe longer. She had to be carried and was groggy for several hours more. She was still affected the next day.
I don't know if using gas is common. My grsndson's dentist is forward acting. If I could, I'd use the gas in the office method. It is quicker and easier on the child. My grandchildren love going to the dentist who uses a lower amout of gas for fillings too. The kids don't have a memory of the procedure.