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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 things to focus on for efficient clinical photography. "Focus" is actually one of them! But, is it manual focus, or auto-focus?
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.
A higher resolution camera is NOT the goal. The goal is a camera that you can USE.