Big crown and pushing forward from lower teeth
If it is you upper right front incisor, it is likely that the lower incisors which are crooked and drifting forward have slowly been pushing your upper incisor forward. This would make it look even bigger over time. If you are having pain, you should have it evaluated immediately and then it is possible to have a new crown made which could look smaller. You will either need to do orthodontic treatment to move the lower offending teeth back, or you will have to grind the lower tooth back significantly which may not be a good idea.
Douglas Jopling, DDS
Dallas, TX area
I think you are trying to show the crown on your bottom left in the back of your mouth. It sounds as if the crown is starting to fail and possibly the tooth needs a root canal. More information is necessary to make a diagnosis. Forty years is a long time for a crown to last. You have gotten your money's worth out of this restoration. Visit your dentist so an exact diagnosis can be made. At the very least you may be getting a new crown.