Etiology and Pathogenesis
Endodontic disease occurs when the dental pulp (the connective tissue, blood vessels, and nerves in the center of the tooth) becomes infected or inflamed. The pulp is protected from bacteria by the impervious enamel covering the dentin of the crown. Damage to the enamel, either through trauma or from a developmental abnormality that allows bacteria to reach the pulp, will result in pulpitis and possibly pulp necrosis. Blunt trauma can also injure the pulp beyond its ability to heal. A tooth with direct exposure of the pulp at a fracture site requires endodontic treatment or extraction. Teeth are fractured from external trauma (eg, catching rocks, automobile impacts, aggressive play) or from biting on inappropriate objects (eg, bones, hooves, hard toys, rocks, fences, or cages). An inflamed or dead pulp releases inflammatory mediators into the periradicular tissues, where they exit the diseased tooth through the apical delta at the root tip or through lateral canals. The tissues at these sites develop a granuloma, cyst, or abscess. Caries are a bacterial infection of the tooth (see Dentistry: Dental Caries in Small Animals). While they are uncommon in dogs, when they occur, they can quickly infect the pulp.
Clinical Findings and Lesions
A discolored tooth is evidence of previous trauma and hemorrhage from the pulp into the dentin. An inflamed pulp can heal after a minor injury. However, more severe trauma will cause irreversible pulpitis, eventually leading to necrosis. Because dental pulp has no collateral circulation, injuries heal less readily and extravasated blood remains in the dentin where it deteriorates rather than being removed. The most obvious indication of endodontic disease is a fractured tooth with exposure of the pulp chamber. The pulp bleeds for only a short time. After the initial injury, it may appear as a red dot at the site of the exposure if the pulp remains vital, or as a black hole if it becomes necrotic. Either way, treatment is required. Drainage is most commonly through the fracture site. However an apical abscess can occur if the site becomes occluded. The skin ventral to the medical canthus of the eye is a common site for swelling and purulent drainage from a fistula due to infection of a maxillary fourth premolar. This can also cause an intraoral parulis, a red draining fistula, above or at the mucocutaneous junction adjacent to the tooth. An abscessed maxillary canine tooth in dogs can cause swelling along the side of the nose; in cats, the swelling is often rostral to the eye. Veterinary patients rarely give any indication of discomfort, even for syndromes that cause severe dentofacial pain in people.
On a radiograph of a tooth with endodontic disease, the typical lesion is a periapical lucency, ie, an irregular circular lesion with decreased radiopacity around a root tip. Throughout life, the pulp produces dentin on the inside surface of the pulp cavity, resulting in a constantly decreasing cross-sectional pulp size. A necrotic pulp discontinues its normal dentin production, appearing less mature than the pulp of the contralateral or adjacent teeth. Conversely, an inflamed pulp produces dentin at an accelerated rate. If there is generalized pulpitis, the effect can be an apparent accelerated aging of the entire tooth with an abnormally narrow root canal space and pulp chamber.
Teeth with irreversible pulpitis or pulp necrosis require either endodontic treatment (root canal therapy) or extraction. Except in very young patients, one of these options is indicated for every tooth in which a fracture has exposed the pulp chamber. Canine teeth in dogs and cats and carnassial teeth (maxillary fourth premolars and mandibular first molars) in dogs are considered strategic teeth. Root canal treatment of these teeth is much more comfortable for the patient than extraction, and allows continued function. Working dogs such as military, police, or performance animals may require full crown restoration. Extensive loss of premolar or molar teeth may sometimes require crown restoration to restore the cervical architecture for periodontal health.
Last full review/revision March 2012 by Jack Easley, DVM, MS, DABVP (Equine); Gregg A. DuPont, DVM, Fellow AVD, DAVDC