I need help to figure out why nitrous oxide is not routinely used in dental clinics?

Nitrous Oxide use: First, you have to be trained and not every dentist is. Secondly, and more importantly, dental insurance companies do not generally pay for this service. Dental clinics are looking to cut costs and would have to offer this premium service at no charge, or the patients would have to pay out of pocked. Both scenarios are unlikely. You generally get what you pay for in this world.