This is one of the biggest problems with the 2012/2015 edition of the standard, but it has been coming on for a long time. Remember that Category 3 derives from Level 3 which in turn derives from Type II - originally written for the "dentist practicing alone". It's origin and it's current use are at odds, so the text is trapped. It cannot change to fully reflect the new applications allowed for Category 3, and it remains a standard intended for a dentist's office. The questions you raise are completely alien to the environment, and that is why we are never going to be able to use this Category as Chapter 4's category definitions conceive it.
The proposal for the 2018 is to pull dental out completely into it's own Chapter, which would allow the writing of a proper medically oriented Category 3. We'll see what NFPA decides.