Toothache with no cavities?!

Toothache with no cavities?

Hi, hope someone can help. My 12y/o developed a toothache in his lower rear molar. Dentist ran full xray's and no cavities. Tooth hurts to touch/eat as well as the gum. He's now complaining of teeth on the other side of his mouth hurting, one more of a pressure ache, the other same symptoms as the 1st one. I've called his pediatrician, and he's perplexed as well since he shows no other signs of sickness. Calling the dentist again, but anyone have any other ideas?

2 months ago
Additional info - after the 1st set of xray's showed nothing, the dentist ran another different set of xray's to see more. I don't know.

Another question, if it is an infection, would it cause pain in the other side of the mouth?

Also, no fever, no swollen glands, nothing???

It sounds to me like my own symptoms which were of an absess, but if the x-rays were clear then it could be that he is clenching his teeth together too hard for some reason. My daughter used to have a severe "toothache" that turned out to be the face she was pulling when playing a computor game. Check if he is tightening his face muscles or biting down hard when playing on a console or similar thing.

Edit
Was thinking about the time years back, when I had infection in both ears, made my whole face hurt! Go doctors and get that checked-just a thought.