What can a discomfort behind front left tooth in the palate be? had ct scans and x-rays down and it doesn't show anything. pain radiates ear & neck.

Front tooth pain: Seek a second opinion from an oral surgeon. It is not uncommon to "miss" lesions despite x-ray and ct scans (as not all ct scans, especially if they are not specific cts done for dental and jaw diagnosis) are not sensitive enough to find lesions. If the pain is with a tooth that had a root canal, it is possible the root canal has failed. No diagnostic test is conclusive., only clinical judgment.

TMJ + Neck + Back +: Sounds like a tmj/muscle dysfunction problem that is treated by a dentist. Select a dentist that routinely treats TMJ with functional orthopedic type appliances. Many dentist treat tmj, however only about 5% are really good at it partly due to familiar with a wide range of modes of therapy to better customize the treatment specifically for your conditions.

Two issues?: One of your front teeth can be non-vital or going non-vital without showing that with any imaging technique. See an endodontist to evaluate the vitality and health of your upper front teeth. The radiating pain is likely not associated with the pain on the front tooth. Further testing is warranted and cannot be done over the internet.