A common feline oral malady is tooth resorption (TR). Greater than half of all cats older than three years old will have at least one tooth affected by resorption; it affects dogs less frequently.   These tooth defects have been called cavities, neck lesions, external or internal root resorptions, feline odontoclastic resorption lesions (FORLs), and cervical line erosions.

Tooth resorptions are usually found on the outside of the tooth where the gingiva (gum) meets the dental hard tissue. The lower jaw premolars are mostly affected, however tooth resorption can be found on any tooth. 

The cause is unknown, but theories supporting an autoimmune response, calicivirus, and metabolic imbalances relating to calcium regulation have been proposed.  The resorption generally starts at the cemento enamel junction (gum line) and progresses inward, eroding sensitive dentin. Once the resorption is exposed to the oral cavity, bacteria invade causing pain and jaw spasms. Increased salivation, oral bleeding, or difficulty eating are other signs. Unfortunately, most times there are no outward signs. It is up to the veterinarian or astute owner to diagnose tooth resorption.

There are five recognized stages and three types of tooth resorption. Initially in stage 1, only an enamel defect is noted. The lesion is usually minimally sensitive because it has not entered the dentin. In stage 2, the lesion penetrates enamel and dentin. When resorption progresses into the pulp chamber (nerve) stage 3 has occurred.  In stage 4, large amounts of the tooth’s hard structure have been destroyed. By the time stage 5 has occurred, most of the tooth has been resorbed, leaving only a bump covered by gum tissue.

Intraoral radiographs (X-rays) are essential to evaluate all the teeth to determine the best course of therapy. Depending on what is seen on the visual patient exam and the intraoral X-rays (tooth resorption type 1, 2, 3), treatment involves following the resorption until it is exposed to the oral cavity, extraction of the entire tooth and roots, or a partial tooth extraction.  In cats affected by stage 5 without inflammation, treatment is not necessary.