To tell the story of the mouth, you want to learn how to take good clinical photographs. Intra-oral photographs are good, but DSLR's are the BEST!
The three parts to an exposure: F Stop, Shutter Speed, and ISO setting. There are, of course, other variables, but these are the key components to work on your camera.
Taking photographs with a DSLR seems like over-kill BUT you get so much better information that the patient can understand. Plus, you get the same quality and consistency over the years of your practice!
A higher resolution camera is NOT the goal. The goal is a camera that you can USE.