How much CT radiation exposure is safe?

Have lower jaw pain under ear and Neck for 8 months now. I have been to dentists, endodontist, oral surgeon, ENT, neurologist GP for my jaw and neck pain. It's constant sore,burning pain in jaw under ear and neck for 8 months now. I have small lump like spots in jaw under ear and neck which hurts to touch. I have mild swelling spots in under ear jaw and neck which is tender and sore. Neuro want me to take MRI brain with contrast to see if nerve is ok.   I went to my GP.  My GP wanted me to take CT neck soft tissue scan with contrast instead of MRI. So don't know which one to take. dentist suspect tooth fracture in #46 and said to extract it. Endo couldn't see any fracture. no diagnosis. does CT scan on neck soft tissue shows same as MRI brain? Is my GP right? she said not to do mri and to do CT. which one should I do?I had many dental periapical  x-rays,7 panaromic x-rays,3 dental CBCT scan in 7 months .Is it harmful to take this CT neck now? how much of radiation exposure is ok?