Just wondering. 25 years ago I had nasty cavity on one of my molars. The dentist drilled and filled it and we called it good. Yesterday that filling came out so I went to the dentist today for a new filling. She says I need a root canal and a crown. Why is that? Nothing seems to have happened to it in the mean time. I have no pain or sensitivity. There is simply a hole in my tooth where the original dentist drilled it 25 years ago. I'm not sure why she can't just fill it again and we'll worry about it in another 25 years. She didn't do a very good job of explaining it.