There's no real need to reserve nitrous oxide for medical (including dental) use. It's not a scarce natural resource or anything and can be manufactured cheaply from commodity inputs. Medical use has been steadily declining due to concerns over side effects and availability of superior alternatives for anesthesia.

> superior alternatives for anesthesia

Two of my kids were born using nitrous as anesthesia. This was years ago in San Diego, CA. I very clearly remember leaning in to my struggling wife and trying to motivate her: "Honey, remember, you need to breathe for the nitrous to work. Don't just hold your breath and bear down. You've got to breathe."