I had an old root canal RE infect, and since I didnt feel any sx, it went on for a long time. When discovered they found it had eaten a hole into the floor of my sinus cavity. I guess I was lucky, in that a strong course of antibiotics after the apicoectomy (they sawed off the root of the tooth that was touching the sinus, and leaking infected material) I was just fine. I had that root canal done originally at one of those fancy pants places that was more like a spa. I was told that all was well. The surgeon who removed the root of the tooth, told me i have VERY long roots on my teeth, and its common to miss that top tip on long roots. He fixed it, and I havent had a problem since. My sinus healed after getting all that material out, and no more weird sinus sx.

Hang in there. I hope yours resolves as nicely after repair.