Feline odontoclastic resorptive lesions (Proceedings)

Feline odontoclastic resorptive lesions (Proceedings)

Apr 01, 2008
By dvm360.com staff

Resorption of teeth

Resorption of the teeth can be either external or internal. Internal resorption occurs when the tooth has been traumatized causing an inflammation of the pulp. The resorption starts on the pulpal surface and extends out towards the external aspect of the tooth.

External resorption may occur after there has been damage to the periodontal ligament. There are three types of external resorption: surface, replacement, and inflammatory. Surface resorption is self limiting and reversible. It is caused by biting on hard objects causing localized damage to the periodontal ligament. Once the trauma has stopped, reparative dental tissue is deposited and heals the lesion. Replacement resorption results in the replacement of the dental hard tissues with bone. This type of resorption results in a fusion between tooth and bone called ankylosis. Inflammatory root resorption occurs when there is inflammation in adjacent tissues causing. The resorptive lesions commonly seen in cats and occasionally in dogs are external and a type of replacement resorption.4

Feline odontoclastic resorptive lesions: An introduction

Since most of the current research focuses on cats, this discussion will also focus on cats. Feline odontoclastic resorptive lesions or FORLS are one of the most common oral lesions seen in the cat mouth.1 On oral exam these lesions are usually seen on the buccal and labial tooth surfaces at the cementoenamel junction with granulation tissue filling the affected area. The maxillary and mandibular third premolars, the maxillary fourth premolar and the mandibular first molar are the most commonly affected teeth with the canines and incisors being less commonly affected.2

Etiology, predisposition

While there are countless volumes of research on this topic, the etiology of this disease is unknown. The research thus far has shown that FORLs are seen in cats starting at 2 years of age. The number of lesions increases with age. There is also no clear breed disposition, except that there may be a higher occurrence in purebred cats with Longhaired Persians and Siamese being at the forefront. Neutering is also not found to be a factor. There has been an increase in the prevalence of FORLs since the 1970s. It is thought that with the domestication of the cat, which has brought changes in diet, neutering and vaccinations that this has had an influence on feline tooth development, causing the tooth surface to be less resistant to resorption. 2


Odontoclastic resorptive lesions are a form of external root resorption.4 Normal odontoclastic activity is seen with the resorption of deciduous tooth roots preceding exfoliation.3

The disease starts in the hard tissues of the root surface or cementum. These tissues are destroyed by cells called odontoclasts. The stimulus that causes the odontoclasts to become active is still under much investigation. It can be said that some form of trauma might be causing damage to the periodontal ligament and the cementoblast layer and trigger resorption at the site of injury.2

Resorption in the cementum progresses to the dentin and spreads via the dentinal tubules and thus eventually involves the pulp, the dentin of the crown and then the crown. The enamel of the crown either resorbs or loses its attachment to the previously intact dentin and fractures off. Hence, when one sees the lesions in the mouth on oral exam, we are in the late stages of the disease.4

The resorption phase is self limiting. When the resorption stops, the cells from the periodontal ligament deposit bony reparative dental tissue to replace the lost dentin. This causes a fusion between root and bone called ankylosis. As this reparative phase progresses, the contour of the root becomes more and more irregular or disappears leaving "ghost roots."4,2


Lesions are graded by severity in 5 levels. The grading system is useful for developing a treatment plan. An accurate classification of a resorptive lesion is attained through a combination of a thorough oral exam and dental radiographs.

Class 1 – enamel only
Class 2 – enamel and cementum and dentin
Class 3 – enamel, cementum, dentin and pulp chamber, crown intact
Class 4 – enamel, dentin, pulp chamber, significant weakening or partial loss of crown
Class 5 – no crown remaining, gingiva is in various stages of repair over the former tooth site.5, 2