Tooth resorption is the most common dental problem in cats, with studies worldwide showing a prevalence rate (in cats presented
for dental problems) of up to 75%. Many species of animals as well as people experience various types of tooth resorption,
but no other species experiences the prevalence of this condition that cats do. Resorptions of permanent teeth in cats have
commonly been referred to as feline odontoclastic resorptive lesions (FORLs). They have also been called neck lesions, cervical line erosions, and feline caries.
Our understanding of FORLs has been enlightened by the use of dental radiography and by histologic studies.1,2 It appears that the lesions originate in the cementum, invade into dentin, and, from there, can progress apically (down the
root), coronally (toward the crown), or both ways (Figure 1). Enamel often flakes off if its underlying dentin is involved. Enamel may also be resorbed (but from the inside out) once
the lesion has progressed coronally into the tooth crown. The bottom line is that by the time we can clinically detect even
small lesions by visual inspection or by probing or exploring, we are encountering an end-stage lesion.3 The cause of FORLs is unknown but is under investigation. All tooth-saving treatments have been shown to have poor results.
Figure 1. A schematic superimposed on a dental radiograph of a mandibular canine tooth illustrating the progression of an
FORL. The lesion originates in the cementum (1), invades into dentin (2), and then progresses apically (3), coronally (4),
or both ways. By the time we can clinically detect small lesions by visual inspection or by probing, we are encountering an
advanced lesion. Figure 2. Note the localized, cherry-red, hyperplastic area of gingivitis on the mandibular third premolar.
This is a classic clinical presentation of an FORL. This tooth should be probed with the patient under general anesthesia,
and dental radiographs should be obtained.
CLINICAL APPEARANCE AND DIAGNOSIS
On oral examination, FORLs are often associated with a localized, cherry-red, sometimes hyperplastic area of gingivitis (Figure 2). The teeth most commonly affected are the mandibular third premolars; however, all 30 of a cat's teeth are at risk. An FORL
can be demonstrated on oral examination by gently brushing the suspected lesion with a thin wisp from a broken wooden cotton-tipped
swab or a coarse paper point tip. Gently stimulating these lesions often invokes a strong jaw-chattering response. FORLs are
best diagnosed on oral examination of an anesthetized patient by probing with a dental explorer. Record any tooth crown or
root defects in a dental chart. Other clinical signs that may be associated with FORLs include a bony bulge over the root
of an affected tooth that may occur because of an osteoproliferative response to the root resorption (Figures 3A & 3B). The maxillary canine teeth are most commonly affected with this bone proliferation.
A diagnosis of an FORL requires radiographic evaluation. It is impossible to identify early lesions and make proper treatment
decisions without dental radiographs. Every cat presented for dental treatment should undergo a full-mouth series of dental
radiographs to screen for FORLs. However, it is possible to miss some lesions if you are relying on radiography alone. So
the best diagnostic plan is to combine the findings of a thorough oral examination in an anesthetized patient with the results
of a full-mouth dental radiographic examination.
Figures 3A & 3B. Note the bulge over the maxillary canine tooth root (3A). The dental radiograph (3B) shows evidence of an
FORL with almost complete resorption of the root.