Normal Dental Anatomy

The tooth consists of three layers: the outer layer which is the enamel, the middle layer which is the dentin, and the inner most region which is the pulp cavity. The enamel is a hard calcified tissue that covers the dentin of the crown portion of the tooth. The dentin is a hard calcified tissue forming the middle layer of the tooth and is covered by enamel and cementum, and surrounds the pulp tissue. The cementum is a bone-like tissue that covers the root of the tooth. The pulp cavity consists of the entire cavity inside the tooth and includes the root canal, pulp chamber, and pulp horns. The pulp contains nervous, vascular, and loose connective tissue.

The teeth of dogs have one to three roots. The anatomic root is separated from the anatomic crown by the cervical line known as the cementoenamel junction. The furcation of a multirooted tooth refers to the point at which the roots branch from the crown. The periodontal ligament attaches the tooth to the alveolar bone. The periodontium consists of four basic components: the gingiva, cementum, alveolar bone, and periodontal ligament. The periodontal ligament attaches the cementum of the root of the tooth to the alveolar bone. The attached gingiva is separated from the alveolar mucosa by the mucogingival line. The gingival sulcus is the normal subgingival space that lies between the gingival crest and the epithelial attachment.

Dental positioning terminology is important when reporting dental pathologic conditions. Coronal means anything lying or moving toward the crown, while apical means anything lying or moving toward the apex or root tip. Distal means farthest away from the median line of the face while proximal means towards the midline of the dental arch. Buccal means towards the cheek, lingual means towards the tongue, and palatal means toward the palate.

It is important to be familiar with the deciduous and permanent dental formulas in the dog:

It is also important to know the number of roots of each tooth in the dog when performing small animal dentistry. In the dog all the incisor and canine teeth have 1 root. In the dog the 1st maxillary premolar has 1 root, the 2nd & 3rd maxillary premolars have 2 roots, and the 4th maxillary premolar, and 1st and 2nd molars have 3 roots. The mandibular cheek teeth all have 2 roots except the 1st and last cheek teeth.

Common canine oral pathologic conditions include: variation in numbers of teeth and developmental abnormalities, abnormalities of occlusion, periodontal disease, dental caries, worn teeth, fractured teeth and dentigerous cysts. Accurate diagnosis of these abnormalities provides a baseline for appropriate treatment recommendations.

Variation in Numbers of Teeth and Developmental Abnormalities

Variation in numbers of teeth include oligodontia (less than a full complement of teeth), and supernumerary teeth (exceeding the normal number of teeth). Oligodontia may be a problem in show dogs since missing teeth are considered faults in the show ring. Supernumerary teeth may cause the same dental problems that are associated with persistent deciduous teeth including dental crowding and a predisposition for rapid development of periodontitis. Extraction of supernumerary teeth that are causing crowding is recommended.

Developmental abnormalities include: supernumerary roots, dilaceration, dens-in-dente, and pulpal stones. These developmental abnormalities such as supernumerary roots may be of no clinical significance except when attempting to extract these teeth then it becomes important to know where the supernumerary roots are located. Dilaceration is a tooth with sharply angulated root(s). Dens in dente is a developmental disturbance in tooth formation: the result of invagination of the epithelium associated with cornonal development into the area which was destined to be pulp space. After calcification there is an invagination of enamel and dentin into the pulp space and a distortion of this space and the root contour to accommodate this invagination. A pulp stone is a small mineralized structure that may be located in the pulp canal or chamber and may complicate endodontic therapy.

Abnormalities of Occlusion

Abnormalities of occlusion include prognathic malocclusions, brachygnathic malocclusions, and wry mouth. Other abnormalities include anterior and posterior crossbite, base narrow or linguoversion of mandibular canine teeth, and rostromesial inclination of maxillary canine teeth. When malocclusion results in secondary trauma to adjacent soft tissue, the malocclusion should be corrected by exodontia, crown-shortening and pulp-capping or orthodontic movement of affected teeth.

Periodontal Disease

Periodontal disease is the most common cause of oral infection and tooth loss in dogs and is caused by an accumulation of large amounts of bacteria at the junction of the tooth and the gingiva. A periodontal probe is required to assess the severity of periodontal disease.

Various clinical presentations of periodontal disease in the dog and cat have been previously reported. The usual clinical presentations include mobile teeth, periodontal and periapical abscesses, facial swelling, gingival pockets, nasal discharge, and oronasal fistulas. The unusual clinical presentations include severe gingival sulcus hemorrhage, pathologic fractures, intranasal tooth migration, and osteomyelitis.

Dental Caries

Dental caries is a demineralization and loss of tooth structure. Once dental caries perforates the enamel, the caries can progress rapidly in the dentin, destroying the tooth and eventually resulting in pulpitis and pain. This may be followed by pulp necrosis and periapical infection. The teeth most commonly affected in dogs with dental caries are the maxillary first molar, and the mandibular first and second molars. When dental caries occur in the dog the lesions are often multiple and advanced. Treatment of dental caries includes extraction or restoration of the affected tooth.

Worn Teeth and Fractured Teeth

Worn teeth and fractured teeth may lead to endodontic disease. Endodontic disease refers to disease of the pulp and may be a source of significant dental pain in dogs and cats. Etiological factors of endodontic disease include: dental trauma, rapid attrition (worn teeth), deep dental caries and thermal or electrical injuries. Animals with an acutely fractured tooth with pulpal exposure will hypersalivate, be reluctant to eat, and exhibit abnormal behavior. Over several months the pulp becomes necrotic and the animal is no longer painful until an inflammatory reaction occurs around the apex of the tooth at which time the animal becomes painful again. Animals with chronic endodontic disease may present with facial swelling, sneezing and nasal discharge, and/or fistulas located at or apical to the mucogingival line.

Dentigerous Cysts

Dentigerous cysts occur infrequently in dogs, however, the diagnosis of dentigerous cysts should be a primary consideration in young dogs presenting with oral swellings. Additionally, the possibility of an iatrogenic dentigerous cyst must be considered in those dogs in which a deciduous tooth was extracted or a traumatic episode has occurred in a puppy and subsequently the permanent tooth fails to erupt. Definitive diagnosis of a dentigerous cyst is based on history, physical examination, radiography, and histopathologic examination. Dentigerous cysts arise from the cellular components of the developing dental follicle. The cyst contains one or more embedded teeth and usually surrounds the coronal aspect of the tooth. As the tooth bud continues to develop but fails to erupt, the cyst becomes filled with fluid. Fluid pressure within the cyst results in a smooth-bordered radiolucent cavity typically adjacent to the cementoenamel junction as viewed radiographically. The treatment of a dentigerous cyst usually involves surgical extraction of the affected tooth and thorough removal of the entire epithelial lining of the cyst wall which is submitted for histopathologic examination. Complete excision of the tooth and the cystic epithelium is curative.