TOOTH RESORPTIVE DISEASE OF FELINES (TRDF)

Tooth resorptive disease of felines (TRDF) is a disease of the periodontium of cats. Orally exposed resorptive lesions (RLs) is the term used to describe lesions visible on the tooth's surface. The terms "cervical line lesions" and "neck lesions" are no longer considered accurate and appropriate for this disease. Next to periodontal disease, TRDF represents the second most common dental disease in cats presented to veterinary dentists in the United States. Various studies show the prevalence rate to be between 20-75%. In reality, about 50% of the feline patients presented to the dentist are affected by RLs. Although there is archival evidence of TRDF being around since the 13th century, there has been a marked increase in prevalence since 1970. To date, there is no proven etiology, however, association with domestication is apparent and commercial diets containing excessive vitamin D may be an etiological factor. It is important to understand that, in spite of extensive ongoing research, there is no known definitive cause and the cause may actually be multifactorial. It is rare to find TRDF in feral or wild felines. Because there is no known cause, recommendations for preventive measures can only be speculative.

Pathology always begins on the root surface (out of sight). Odontoclasts, normal cells located within the periodontal ligament, are for some reason activated and begin a pathological resorption of root surface cementum. There are two distinct histological types of root surface resorption: Type I (inflammatory) and Type II (replacement by bone). Type I resorption seems to be initiated by periodontal inflammation; however, replacement resorption is the more common type. Over time, resorptive lesions progress to affect root and then crown dentin.

Most cats are very tolerant of pain and often do not reveal clinical symptoms. Of those patients that happen to demonstrate symptoms, it usually indicates complications have already occurred. The patient may be off their normal appetite, drooling, pawing at the face, "chattering" or having an eating preference that may actually be for harder food substances. RLs are usually discovered accidentally on oral examination. The mandibular third premolar is the most commonly affected tooth and can be considered a sentinel for the disease. Where one tooth is affected, there are usually multiple teeth with problems. Orally exposed lesions are typically found near the gingival margin on the buccal and lingual tooth surfaces and they are often filled with calculus or a layer of granulation tissue. RLs are confirmed by palpation with dental explorer instrumentation. Other common clinical findings are maxillary canine tooth extrusion (supereruption), alveolar bone expansion (alveolar osteitis) that can be observed over the jugum of any canine tooth, and mandibular cortex enlargement. As with any oral disease in animals, examination is not complete until performed under general anesthesia. Full mouth intraoral (dental) radiographs are imperative for two reasons: 1) they reveal far more lesions than oral exam alone; and 2) they determine therapeutic decisions. Tooth resorption (TR) lesions are classified as Type I (inflammatory) or Type II (replacement) based upon radiographic assessment of the alveolar bone and root. Type I lesions occur in the cervical and furcation regions of the tooth. Radiographically, the periodontal ligament (PDL) space and pulp space are visibly intact around the root and there is focal loss of tooth structure and adjacent alveolar bone. There is a normal density of root and bone. With Type II lesions, the PDL and lamina dura are not completely visible and there is a loss of normal root structure. Root structure and alveolar bone take on a similar radiodensity.

Teeth with orally exposed lesions are usually painful and secondarily infected. Complete extraction of tooth material is the treatment of choice. Indications for extraction include orally exposed lesions as well as teeth that may not have RLs, but do have advanced root resorption radiographically. The use of restoratives has shown a poor long-term success rate, and laser treatment is controversial at best. Neither of these treatment options can be recommended.

Extractions are performed surgically with full thickness mucogingival flaps to allow for complete removal of tooth material, alveoloplasty and closure of the extraction site. For treatment planning, pre-op radiographs are essential in order to distinguish between Type I and Type II disease. Type I cases require complete removal of tooth material, not just crown amputation. There are various resources for feline extraction techniques. Atomization (root pulverization with a high speed bur) of retained root tips is inappropriate and to be avoided because of the potential for severe complications. With earlier stage Type II cases, complete extraction is indicated and should be completed. In end-stage Type II situations, where there is advanced root replacement resorption, ankylosis and no PDL or pulpal tissue evident radiographically, crown amputation with intentional root retention is an acceptable alternative. Post-op radiographs should be taken in both cases to verify removal of tooth material. If a tooth is undergoing root resorption that is not advanced and there are no orally exposed lesions, the tooth can be monitored. Annual follow-up radiographs are recommended.