Shark Teeth aka Ectopic Eruptions

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Hey! It’s Me! Dr. Christian!

What do human teeth and shark teeth have in common? Lots. As a former oceanographer turned orthodontist, this subject could not have been more interesting to write about! I spent the first four years of graduate school studying Marine Biology at the Scripps Institution of Oceanography in San Diego, then decided to become a dentist!

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Check out the ectoderm on that fish! These structures, or plates of armor, were made the same way as your teeth!

To understand the connection between your teeth and shark teeth, we first need to go back in time to the origins of teeth themselves. Teeth are derived from the same tissues that make skin, hair, and nails. These are called the ectoderm, or outer layer. Prehistoric fish didn’t have teeth, but rather the ectoderm made outer plates of armor that protected the fish from prey. These plates were literally the fish’s “armor” and were made out of a very hard substance. The same biological machinery that makes these plates also makes the structures of your teeth. It’s no coincidence that the hardest substance in your body is the enamel of your teeth. As evolution developed more creative innovations, these pieces of armor developed into more specialized chewing structures like teeth.

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A tooth’s basic anatomy

The fish’s ectoderm formed in the same way your teeth form, with a very hard outer layer called enamel and an inner layer called dentin.  Over evolution, these plates developed into scales on fish! Special forms of scales, made out of enamel, bone, and dentin become teeth.  These origins of teeth are still found in sharks today.  Shark teeth form from modified scales near the tongue and move outward along the jaw until they are eventually dislodged.  They form continuously in rows. Way cool, right?!

 

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I like to hang out at the CA Academy of the Sciences.  This is a Megadont jaw – These guys were up to three times the size of a great white!

Human teeth today retain some of these forms. Enamel, our armor, is the hardest substance in the body.  Our teeth also form in rows, with the adult teeth budding off from the succedaneous teeth or baby teeth. Unlike sharks, which have a continuously forming rows of teeth, humans have only two sets of teeth.  These consist of 20 baby teeth and 32 adult teeth.  For this reason, if you’re born missing a baby tooth, you will always be missing the same adult tooth.  Sometimes the baby tooth does not dissolve away in time for the adult tooth to erupt into place.  This results in an ecoptic tooth, or double set of teeth.  Just like shark teeth!

Ectopic Eruptions, or shark teeth, are not a cause for alarm, it’s ok! Sometimes this is a simple fix by extracting the baby tooth to make way for the adult tooth to come through.  In some people, a genetic mutation in the tooth forming machinery can result in continuously forming teeth, with tooth formation gone wild, similar to a shark.  The picture below is of someone with this condition, called cleidocranial dysplasia.  Either way, anything can be treated by your pediatric dentist or careful collaboration between orthodontists, surgeons, and pediatric dentists.

 

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This is a patient with multiple rows of extra teeth due to a disorder called Cleidocranial dysplasia.  Dustin in Stranger Things has this condition in real life!

 

 

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