Where did the roots go?

I had a very interesting case last week that further illustrates why dental radiographs are necessary to practice modern veterinary dentistry.  Bailey is a very sweet, 11 year old Golden Retriever that was referred because she had several broken teeth that looked like the upper 4th premolar pictured below.

This tooth did not need any treatment beyond cleaning, but the same premolar on the other side had to be extracted due to advanced endodontic disease and external tooth root resorption. But as often is the case we found some other problems.  The tooth that is pictured above on the lower jaw in the very back of the mouth appeared very normal, but look at the radiograph.

This second mandibular molar should have 2 tooth roots, but as you can see they were missing.

A very similar problem was discovered in the other side.

On the left mandible the second and third premolars had disappearing roots. 

We do not know what causes this problem, called tooth resorption, and it is much more common in cats.  The only treatment is extraction.  The affected teeth were extracted and Bailey did great.