Thanks for your advice. I wanted to mention a few things to get your opinion as well.

1) First, I have no pain in the tooth itself. Now, I suppose this is due to the fact that the nerve was removed during the first root canal. So what you're saying is that there is bacteria hidden in the microscopic root canals and this is somehow leaking toward the sinus region, which is causing this dull, gnawing, aching sensation?

2) I've been dealing with this pain for many years and have been led down many dead-ends. For example, an ENT doctor I saw years back thought it was due to a deviated septum. He recommended a septoplasty, which I did, but it didn't help with anything. I just don't want to get an extraction if it's not the true cause of this pain.

What other symptoms should I have to be positive that this pain I have is due to the tooth? Again, I have no pain inside the mouth at all. The ONLY pain I have is in this area right below the left cheekbone. It's not on the surface but it feels like it's several inches inside the face. I have no pain in the gums, which somehow makes me feel like the tooth is not the cause of the pain. I mean it is possible this root canal infection and the pain are two separate things. Does it surprise you that I can have pain in the area I mentioned earlier without having pain in the gums/tooth etc..?