The open mouth odontoid (OMO) X-ray view does indeed demonstrate structures that are not easily discernible on the lateral views. These structures are the C1-2 articulations or facets. Arthritis of these joints is typically missed without the OMO view. The MRI can pick up on this disorder but the images have to go up high enough to catch these structures and many times they are not captured on the images.
If there is suspicion of a disorder or deformity of the occiput to C2 area, the CT scan is a very good study. Ask your physician if they think that will help with the diagnosis. I am not sure however that dizziness can be caused by arthritis of the C1-2 joints.