The Faculty of Dentistry at Malmö University due a unique study that shows that when you age your jaws decreases. The study was stated in 1949. Plaster molds were made of the jaws of dental students, who were then in their twenties. Ten years later the procedure was repeated, and in 1989, forty years after the first molds, a final round was performed. On that occasion the researchers were in touch with 18 of the original 30 participants.

They found that over those forty years there was less and less room for teeth in the jaw. This crowdedness comes from shrinkage of the jaw, primarily the lower jaw, both in length and width. While this is only a matter of a few millimeters, but it is enough to crowd the front teeth. Science Daily (Oct. 31, 2011)