Had a cleaning, mentioned some occasional sensitivity in a tooth with a large filling I'd had the original silver filling replaced by same practice 2 years ago. They found decay behind the old filling and had to drill out more, but has been okay for 2 years. Just some occasional minor sensitivity. He did sensitivity testing and got nothing on the bite and knocking tests, but when he put the cold on this tooth and the neighboring one, this one was more painful. Doc saw nothing terrible on the xray, but pointed out a part of the root in one Xray that in a certain light maybe looked a little dark and suggested that the root might be dying. Said that when it does eventually die and become necrotic, it's never at a convenient time, so recommends I schedule for a crown and possible root canal. He would start with the crown, look at the root once he's ground off the whole top of the tooth and decide if a root canal is needed. It all seems pre-emptive to me and maybe excessive. But I've never had a crown or root canal before. Shouldn't I be in more consistent, severe discomfort before submitting to a crown and possible root-canal? What are the dangers of waiting and seeing if the sensitivity gets worse?