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Rodent Incisors

12-3 woodchuck skull IMG_7187Rodents have two pairs of incisors that oppose each other; two in the front of the upper jaw and two in the front of the lower jaw. These four teeth never stop growing, and thus have to be constantly filed down. (Squirrel incisors grow about one-half inch a month.) While nipping herbaceous plants and cutting into bark help do this, it isn’t enough to significantly wear down the teeth. When mice, beavers, woodchucks and other rodents nip or gnaw food, they move their jaws in such a way that these two pairs of teeth grind against each other. Most rodents have hard orange enamel on the outer side of their incisors (woodchucks are our only rodent with white enamel), and softer dentine in the back. When the incisors grind against each other, the dentine wears away faster than the enamel, creating a sharp, chisel-shaped edge to the incisors. This, more than anything else, keeps the growth of rodent incisors under control, just as a nail file keeps our nails from getting too long.

If a rodent breaks an incisor, there is nothing to wear down the opposing incisor. The tooth opposite the missing incisor will continue to grow unchecked in a circle until it causes the death of the rodent, either by piercing its skull or by preventing the animal from being able to eat. In the pictured woodchuck skull, the lower left incisor has broken off, allowing the upper left incisor to grow through the woodchuck’s palate and into its brain.

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6 responses

  1. fascinating. love reading your posts. i learn so much. Thank you.

    December 3, 2015 at 7:27 am

  2. Marilyn

    That’s a very impressive photo. I’ve not seen a skull with such a tragedy.
    Now I have more compassion for the porcupines gnawing on the lumber under our camp all night!

    December 3, 2015 at 7:42 am

  3. Penny

    You would think the stump of the broken incisor would keep growing also. Did you find the lower jaw of this unfortunate chuck?

    December 3, 2015 at 7:50 am

    • Good point, Penny! Perhaps it has to be an injury that damages the root as well? No, I didn’t find the lower jaw, unfortunately!

      December 3, 2015 at 8:57 am

  4. Wow! Pretty gruesome.

    December 3, 2015 at 9:03 am

  5. What a horrible fate!

    December 3, 2015 at 9:28 pm

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