He has an awesome system !!! probably just set up wrong internally and externally. I'd be happy to help if the doc will let you change his camera settings.......
I agree completely - that camera is fine for intra-oral work. In fact I would rather see people buy a good used older body and save money than go out and plunk down a ton of cash for capabilities you don't need and probably won't ever use. That said, both Canon and Nikon will relieve you of $6,000 to $8,000 if you let them... Hasselblad will take $60,000 for a nice digital entry level camera. Its all in how big you want to go.
Settings are no secret either and simple as pie.
ISO: 200 on Nikon 100 or 200 on Canon (200 ISO is native low on Nikon - while 100 is native low on Canon - either works fine)
Aperture Priority (AV) use ƒ 22 for intra oral deep depth of field and ƒ 5.6 for full face and less depth of field.
Shutter floats under AV
White Balance needs to be set to either AWB or Flash
The ring flash if ETTL or TTL should cut itself off once it senses a good exposure and provide fine images. I will sometimes bump up the flash output on one side or the other for contrast and creative purposes - but that's not absolutely necessary. I AM a photographer and play with light all the time - so it's just me.
I will sometimes also move the exposure compensation up a little if the histogram shows too little light on the image. (See other threads in this section for discussions on histograms)
Any specific questions should be asked here where everyone will benefit from the answers. Thanks!