I do not think a MRI of the c-spine will diagnose tmj but it may show the affects of it. My herniated discs (C5,6 & 7) seemed to be related to my tmj. Although my spinal MRI seemd normal (except for the herniations) based on medical reviews it was a neuromuscular dentist who looked at them and based on some mathematical measurements he did on tracing paper he put over the MRI films (I had obtained copies for myself from the the Imaging center) he pointed out my atlas and axis (C1 & C2) were rotated toward the left and off center which he felt caused the other discs to become herniated as well as other tmj symptoms I was experiencing. According to him if either one of these verterbrae are even slightly off center they can cause a lot of problems and the way they can become off center is through injury, a deviated jaw and/or over working facial muscles which can push things out of alignment.