From Gale:
We all know that a sinus infection can cause a toothache, but did you know it also works the other way? Thanks to Jane, I did not cancel the appt. Today I went back to the dentist almost embarrassed to ask him to look at my tooth again. He looked into my mouth and said “Oh you poor thing!”
My tooth had cracked, but when I was there a few weeks ago, it wasn’t as obvious as it was today. Unfortunately, it cracked all the way through the whole tooth, so it can’t be saved. But that’s not the lesson learned. Food was caught in the crack and it was infected. The lesson learned is that this may have been the cause of the sinus infection, and maybe why it wouldn’t go away.
http://www.ehow.com/way_5640585_bad-tooth-cause-sinus-trouble_.html
Oh, and no problem with the dentist. The internet tells me it can be very difficult to diagnose.
Jane's Lessons Learned 