Quote: You should talk to @pathdoc, who is a pathologist who uses a similar setup.
Speak of the Devil and he appears.
Welcome, OP.
The threads may be dated, but the basic principles of photography never change.
At one stage Pentax had a 100mm macro lens and accessories specifically set up for dentistry work:
SMC Pentax-A Dental Macro 1:4 100mm (for legacy fanatics): Micro Four Thirds Talk Forum: Digital Photography Review or
SMC Pentax-A Dental Macro 100/4.0 – B I T Z
The current Pentax 100mm macro lens (the 100/2.8 WR) has the ability to do 1:1 reproduction without the use of close-up lenses, and both OEM and third-party ring flashes are available. I initially bought one of these to use in my anatomical pathology work, but had to transition to a 35mm when I found the field of view too narrow for forensic autopsy (whole body) and close-up large specimen work. These are not handicaps I would anticipate you facing, and given that one of the design purposes behind a 100mm macro is to photograph wet and slimy things at a significant remove from the lens (mostly frogs, insects, etc. in the field), it might be ideal for your intra-oral work, especially towards the rear molars and everything posterior.
The Pentax units are either analogue TTL protocol (e.g. the AF080C) and require older digital cameras - *istD, *istDS, *istDS2, all long-out-of-production - to get the best out of them, and for the more modern bodies are quite expensive (AF160C), but you may be in a position to absorb that as a business cost. Any of the currently available or some more recently superceded Pentax digital bodies will suit you down to the ground and are not hard to operate, and you don't have to break the bank in order to get a good one. They will all be fine, especially if they're being used in the relatively easy-wearing setting of a medical practice, and the in-body image stabilisation should help you get crisp, clean shots.
I haven't actually used the AF160C ring flash so I can't speak as to its utility, but perhaps someone who has can chime in at this point and let you know the ups and downs.