Adjust crown or need root canal

Almost 3 years ago I had two teeth broken when my dog pulled me face first into the side of the house.  On the front left tooth, my dentist then said a root canal was not needed and just put a crown on it.  It has been sensitive to cold ever since ( I haven't not been able to drink without a straw or bit into anything cold since ) and hasn't gotten any better.  4 days ago I woke up with excruciating pain in this tooth and nothing helps, it just continues to throb.  Even brushing that tooth or barely touching it causes extreme pain.  

I can't see my old dentist, so I found a new one who said it looks like the crown may be slightly loose and need adjusting, also the way my bite is I bite harder in that spot.  She said if that doesn't work, then we'll know it needs a root canal.  They can't even get me in for that for a week, and if that doesn't work I'm looking at another week or two after that before I can get in to get it fixed.

I went to another dentist to get a second opinion, and he thinks I definately need a root canal.  How do I know which one is right?  I would think if it were from the bite or the crown it would have been gradual and not happened all of a sudden, but how do I know for sure.  Both dentists did x-rays.  Help!

[Ania778]

if you need a root canal you usually get tenderness high up at the top of the root, which you can feel as a dull ache if you press your finger against it.  If the nerve is completely dead you normally would not be able to feel cold.    However, the fact that your tooth has been excruciatingly painful recently sounds like something is up.  Your former dentist may be right.  It might be that you have bruised the root by biting into something hard recently.  It's sometimes impossible for a dentist to tell without going in and doing a canal because you might have a tiny fracture of the root because of your accident and no x ray can pick that up.  However, having a hard bite can cause you to create a similar sensation and yes it can be very painful.   If it were me I'd go with dentist number one and try the less invasive option first to see if correcting the bite helps relieve the pain.  At some point you probably will need a root canal on that tooth from what you say but I would never rush into this if you are given another option.   It's fairly easy to adjust the bite and if it is causing the problem the relief should be instantaneous.