Feline odontoclastic resorptive lesion of the lower third premolar (407) of a cat.  The caudal aspect of the tooth is affected, with gingival tissue partially filling the defect.
<a href="//commons.wikimedia.org/wiki/User:Joelmills" title="User:Joelmills">Joel Mills</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>