My tooth hurts!?

My second to last molar on the right side has been bugging me for a while. It bothered me for a few weeks and then went away for about a week and now it kills. It's sensitive to hot and cold and throbs. I've gone to a dentist and he wants to put a cap on it but he said he wasn't even sure what was wrong with it. I'm only 18 and don't think that I have a cracked tooth and don't want to start doing caps if he doesn't know what's wrong. I'll probably go get a second opinion but was wondering if any dentists out there had any thoughts about what could be wrong?
Answer:
Well, usually, if it is sensitive to hot, cold and throbbing, this is a good indication it needs a root canal. I've had 3 and may be getting another very soon. I'm going in tomorrow because my tooth is slightly throbbing. However, if you need a root canal, it really isn't that bad. My issue is sitting through it because I get anxious in the chair. Root canals, if done correctly are painless and once finished your pain should be gone. See an endodontists if this is the case. You want to be sure it is done correctly. You don't want an inexperienced dentist doing a root canal.Hope that helps.

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It could be infected.

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