Crown - teeth

I had a crown fitted only 4 days ago. It has come off while brushing teeth. The dentist put it on to check fit but could not get it off again. He said it will not come off. It is 'friction held'! Going next week to see him. What should I say? anyone else had the same problem? I have got other crowns that have been on for over 30 years with no trouble. all of them have cemented or glued on.