How do I know for sure if I need a root canal or not ?

Hi there,

I hope someone can help me since this has been bugging me alot lately. Just this afternoon I started getting really sudden and quite extreme pains in my tooth. It's a tooth that has gotten one deep filling and has been sensitive to cold ever since. The dentist however said that this is normal since it was a fairly deep filling. I believed her. Anyways, it has literally just started aching and it's hurting alot. Now it's not sensitive to touch to the point that it hurts when I simply touch it, it's not swollen around it or discolored and it's also not sensitive to heat or when I eat. Now I'm scared that I need to get a root canal and I hear that those are fairly easily diagnosed. How can I know for sure if it's not just a severe tooth ache, wait it out? Either way I'm going to go get an x-ray of it and go to several other dentists but this is just something that is on my mind. I just took Ibuprofen 600mg and after 15 minutes the pain went away and it stays away for a couple hours and suddenly comes back hurting like heck. Are root canals painful or are they less painful than most people make them out to be ? Hope someone can help me out soon.

Thanks already,

RC