One of my molars had been root-canalled years ago, and had cracked, as they often do after this treatment. The dentist filled it twice on condition that the next time it would have to come out. You can see the temporary filling in the top photo.
The crack is on this side. One of the three roots broke when the main bit of the tooth came out, so getting the bit of root out took a while. The long white thing is the filling of the root canal.