Wednesday, 7 September 2011

When teeth go wrong!

Sometimes, whilst looking at thousands of teeth, you notice something that isn't quite right. This is one of those things:

A tooth with two crowns and one root... weird, eh?
Looking at the top front teeth (the incisors) in the upper jaw
of a c. 4-6 year old individual. Medieval.
Adult humans generally develop the same number of teeth.  Most of us have (or originally had, prior to dental intervention) four incisors, two canines, four premolars and six molar teeth in our upper and lower jaws.  It's fairly common however, for some teeth to never form (agenesis). For example, up to a third of the population is congenitally missing at least one of their wisdom teeth  - the final molar teeth to erupt.

It's much rarer to see instances of too many teeth (hyperdontia).  And it is rarer still to see teeth like the one in the picture above.  All of the baby teeth form in the womb, ready to erupt in the infant a few months after birth. This starts in the sixth week of embryonic development, when enamel-forming cells imbed themselves into the site of future primary teeth. At this point, not more than eight weeks into development, a genetic mutation must have occurred to produce such a tooth. Perhaps too many tooth buds initiated, perhaps one divided into two.

Of course, in all likelihood this unusual looking tooth wasn't even noticed, by the child or his family.  Had the child lived, it would have been replaced by the permanent teeth coming through about six years later and we would have never seen it.

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