I had a tooth with a large filling in it that had been there for probably 30 years. I fractured the tooth while chewing one day. The dentist said it was a clean fracture and it didn't need a root canal. He prepared the crown and 3 days after putting the temporary on, it started to hurt and needed a root canal. How can the tooth go from not needing a root canal, to needing a root canal within 3 days? It doesn't make sense to me. The root of the tooth was perfectly healthy before the crown was done.