If you continue to have pain and the dentist can find nothing wrong, you may ask about the possibility of trigeminal neuralgia as the cause. This is pain caused by one of the cranial nerves. Your dentist should know something about it but it is treated by a neurologist.
Here's a link to more information. There is a link to a diagnostic questionnaire from there.
http://www.fpa-support.org/aboutfp/index.html
Did the dentist do an x-ray to see if there is a sinus infection? I had that problem a few years back, I begged the dentist to remove an aching tooth but an x-ray revealed a pocket of infection compressing the nerves under the tooth.