Dental treatment before rad denied by insurance

Hi-
I'm not sure if this is the right forum for this. I'm a 53yoM with SCC of the tongue. I completed chemo/radiation at Mayo. Prior to the treatment they required dental examination, building a radiation shield and create flouride treatment trays to use after treatment.
My insurance Blue Cross Blue shield of MN has denied the claim. I then provided them with the letter from Mayo saying that this was needed and they had one of the physicians on their payroll review it and that person served it not medically necessary.

Has anyone else dealt with this situation successfully?
Thank you!