Teeth move throughout life. Even after the adult teeth have come in, they continue to move forward. If there is space between certain teeth or you have lost a tooth, the adjacent teeth may shift towards the empty space. If a lower tooth is lost, the opposite tooth in the upper jaw can move downwards into the gap. These movements can change the way your teeth meet and can cause undue stress and pressure. Sometimes you can get jaw pain as a result.
How does one treat this?
This can be fixed by restoring the contact relationship between teeth with a fixed or removable appliance. An artificial tooth will sometimes be needed to close a gap left by a moving tooth.
Reconstruction is done in a way as to evenly distribute the loads on all the teeth so as to match the position of your original teeth.