I had a new cap on my last tooth in the back about two weeks ago. It seems fine. The one next to it (two year old cap) is now sensative to cold and hot indicating that it is not happy (me neither.) I ASSUME that it may need a root canal or maybe it just got kicked around a little during the caping of it's neighbor. Anyway - if I need a root canal how will the dentist get through the cap and how will he repare it? Is it possible that I don't need a root canal and it just is sensative from the work on the other tooth?

It is possible that your other tooth just is sore from all of the work done on the one next to it. But, it is also very possible that you will need a root canal on it. In order to do this, your dentist may just drill a hole through the crown to do all of the work and then fill it like he would a cavity. As the tooth already is crowned and therefore has the added support, this will probably work out just fine. However, crowns are almost never salvageable after removal, particularly relatively new ones as they often are broken in half to remove and in that case you would need a new crown. But there is a a very high likelyhood that the work can be done with the existing crown and then just filled.