Dear Christopher Cat: When my cat yawns, I can see that an area of her gums is red and swollen. I took her to the veterinarian who said she has a resorptive lesion, which is something like a cavity.

We scheduled an appointment with the veterinary dentist, but I want to learn more about resorptive lesions before the visit.

Christopher Responds: Resorptive lesions occur when the body dissolves and absorbs portions of a tooth. A small hole may appear, or enough of the tooth may be resorbed that the crown of the tooth fractures.

Although tooth resorption is the most common dental disease in cats, its cause is unknown. It occurs most often in older females; purebreds are more commonly affected than mixed-breed cats. Another risk factor is ingesting too much vitamin D.

Clinical signs include an area of reddened gum covering the lesion, mouth pain, bad breath, drooling, head shaking, pawing at the mouth, lethargy and decreased appetite, especially for dry food.

Sometimes the tooth’s root is resorbed, so dental radiographs (x-rays) are needed to help the veterinarian determine how to treat the tooth. Usually the affected tooth is extracted.

Other names for resorptive lesions are feline odontoclastic resorptive lesions (FORLs) and neck lesions, because they often start on the neck of the tooth, the area between the tooth’s crown and root.