You are correct, it is not a "formal interpretation", but an opinion from a NFPA staff member.
Thank you for posting that, I really appreciate it.
As to the letter, The requirements for hospital grade receptacles is not just contained in 517.18(B) and 517.19(B)(2).
517.61(C)(2) specifically requires hospital grade receptacles to be used in Other than hazardous (Classified) Anesthetizing Locations.
A dentist's exam room that utilizes Nitrous Oxide would be classified as an Anesthetizing location in accordance with the definitions of that location.
Here is the definition
Anesthetizing Location. Any area of a facility that has
been designated to be used for the administration of any
flammable or nonflammable inhalation anesthetic agent in
the course of examination or treatment, including the use of
such agents for relative analgesia.
Here is the definition of relative analgesia;
Relative Analgesia. A state of sedation and partial block of
pain perception produced in a patient by the inhalation of
concentrations of nitrous oxide insufficient to produce loss
of consciousness (conscious sedation).
I can not see where a dentist's exam room would not fall under these definitions if they are using nitrous oxide during their procedures.
Chris