What is the difference between sinusitis and a tooth infection?

Different structure: Sinusitis is inflammation of your sinuses, most often due to an infection. Tooth infection is an abscess from bacteria infiltrating your bone through a decayed tooth. You can have one and not the other.

Cause: A tooth infection usually is a root canal or gum abscess. In upper posterior teeth if this abscess is near or in the sinus, it can also cause a sinusitis. A sinusitis is more often caused by a virus (cold) or bacteria