The unique study started 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.

"We found that over these forty years there was less and less room for teeth in the jaw," says Lars Bondemark, professor of orthodontics, who analyzed the material together with his colleague Maria Nilner, professor of clinical bite physiology at the College of Dentistry, Malmö University .

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.

"We can also eliminate wisdom teeth as the cause, because even people who have no wisdom teeth have crowded front teeth."

How much the jaw shrinks is individual, but for some patients the changes are sufficiently great for them to perceive that something is happening to their bite.

"In that case it's good to know that this is normal," says Lars Bondemark, who maintains that dentists need to take into consideration the continuous shrinking of the jaws when they plan to perform major bite constructions on their patients.

"We're working against nature, and it's hard to construct something that is completely stable."

Why the jaws change throughout life is not known, but the magnitude of the change is probably determined by both hereditary and anatomical factors, including what the patient's bite looks like.

Note: If no author is given, the source is cited instead.

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