A study that followed a cohort of dentists over 40 years has shown that the size of our jaws decreases with age.1
The study, from the Faculty of Dentistry at Malmö University in Sweden, started in 1949. Plaster moulds were made of the jaws of dental students, who were then in their twenties. Ten years later the procedure was repeated, and in 1989, 40 years after the first moulds, 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 40 years there was less and less room for teeth in the jaw,' said Lars Bondemark, professor of orthodontics, who analysed the material together with his colleague Maria Nilner, professor of clinical bite physiology.
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 millimetres, 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,' said Professor Bondemark.
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.
Professor Bondemark 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.
Tsiopas N, Nilner M, Bondemark L, Bjerklin K . A 40 years follow-up of dental arch dimensions and incisor irregularity in adults. Eur J Orthod 2011 [Epub ahead of print].