I was fortunate in that the radiologist who did my CT scan suggested my chronic sinusitis originated from the root of a tooth from an old root canal. I had been sick for 4 months. An oral surgeon told me I could either have it extracted or see an endodontist to try to save it. I did the later and tooth and sinus have been well for the past 10 months. He did the root canal over. He said it’s a risk with root canal teeth. I never had tooth pain because there is no nerve.