I used to get 4 or 5 sinus infections a year. Had my amalgam fillings replaced with composite fillings, and root canals removed. Haven't had any sinus problems since. Teeth were not giving me any problems at the time either.
I'm sure there are other reasons for sinus problems, but keep this in mind if you have any of the above in your mouth. There is a direct correlation between each tooth, and certain organs, or body tissues through the meridians. I had other medical issues that cleared also.