There are many causes for worn teeth in a dog or cat. The most common is pruritis (itching and chewing), because hair is very abrasive. This will commonly cause severe wearing of the incisors, although the canines can also be affected. This can progress all the way to the gumline, and occasionally below. Dogs that chew on tennis balls or other abrasive toys (think of tennis ball as a scoring pad), will often wear their smaller front cheek teeth (premolars), and the back aspect of the canines. This abrasion won't do much over the course of one day, but chewing every day for years can cause significant wear. Another cause is chewing on things like fences, which will wear down the backside of the canines. Finally, malocclusions can cause two teeth to come together and wear on each other.

Worn teeth look like fractured teeth, but usually are not a significant problem. If the wear occurs slowly, the tooth will respond by laying down extra tooth structure (dentin) in response to the tooth loss to protect the pulp. This is similar to the way that our teeth respond to deep cavities. If this occurs, the tooth will generally stay alive, and not require any additional therapy. The exposed dentin in the middle of the tooth will stain a light tan to medium brown. An instrument will not be able to enter the root canal. If the tooth is broken, or the wear occurs too fast or continues too far, the tooth will become endodontically involved. These teeth will generally have a dark brown to black center, which will allow an instrument into the canal. These teeth require either root canal therapy or extraction.

There are instances, however, that the teeth don't follow the above descriptions. On occasion, wear can occur quickly enough to infect the tooth, however the tooth will live long enough to lay down a protective layer of dentin before it dies. These teeth will look like a vital, worn tooth on the outside, but will be dead on the inside. The only way to tell for sure is by dental radiology. Dead teeth will have a wider root canal than their vital neighbors. For this reason, I recommend radiographs on all significantly worn teeth.