Hi Joann,
Both CT and MRI scans are used in the oral cavity. The MRI is considered by many to be the "gold standard" for soft tissue imaging. When combined with a contrast agent, very high resolution images can be obtained with MRI.
My head & neck surgeon has told me more than once that scans in general only offer a piece of the diagnostic information. His opinion is that the visual and palpation exam is the most important (and the biopsy of course).

If your doctor orders an MRI be sure to wear hearing protection (they are noist machines) and don't wear any metal items. Most MRI scanners are very confining as well and if you are claustraphobic you should request medications to allow you to relax. I have had a number of them now and for me it's no big deal.