Pathology radiology most pertinent dianostic

Endodontics is the branch of dentistry dealing with the diagnosis and treatment of pulpal and periapical disease. When confronted with a traumatized tooth, the veterinarian must be able to recommend extraction, root canal therapy or vital pulp care. Intraoral radiographs offer the most pertinent piece of diagnostic information to illustrate what is going on below the gum line.

Jan Bellows DVM, dipl. AVDC, dipl. ABVP

The pulp is contained within the root chamber and canal portions of the tooth. The pulp system is divided into two parts: the pulp chamber located in the crown, and the root-canal system emerging from the floor of the pulp chamber extending though the root(s) into the periodontal ligament in the periapical area.

Image 1 shows enhanced periodontal ligament at the root's apex with digital radiography.

Radiographic anatomy

A dental X-ray shows two-dimensions of the tooth and surrounding structures that are three-dimensional objects. Often multiple radiographs of a particular area are exposed and evaluated to make decisions. Digital dental radiography provides instant images without processing and allows the clinician to enhance images (see Image 1).

Image 2 shows normal apical anatomy in a dog's mandibular canine showing consistent lamina dura.

In a healthy tooth, the periodontal ligament space is surrounded by a compact layer of bone called the lamina dura. As pulpal infection spreads to the periapical tissues, bone is resorbed, the periodontal ligament space appears wider and/or the lamina dura loses its continuity (Images 2-3).

Image 3 shows periapical disease of a cat's maxillary canine, displaying loss of the apical lamina dura and periodontal ligament space.

Pulp width decreases with age as pulpal odontoblasts produce dentin, which lines the pulp chamber. In the young dog or cat, less than 9 months old, the pulp chamber will be wide occupying a majority of the tooth. The apex will also be open (Image 4).

Image 4 shows wide pulp chamber and open apex.

In the older dog or cat, the pulp chamber will be very thin and barely radiographically observable (Image 5, p. 18S).

Image 5 shows thin pulp chambers in the maxillary central incisors of an 8-year-old dog.

Radiograph interpretation

Early in the disease process radiographs might appear normal even with pulpal necrosis because at least 10-percent bone loss must be present in an area to radiographically notice periapical disease.

Image 6 notes the root fracture in the mobile maxillary incisor.

The radiograph of the endodontically effected tooth is examined in an orderly and consistent manner. First, the crown and then the root(s) are inspected, followed by the root-canal system, the lamina dura and periapical area.

Image 7A shows pulpal exposure of a premolar tooth caused by tennis ball chewing.

Crown pathology

The determination of pulpal exposure is key to the treatment of endodontic disease. When the pulp is exposed to the oral environment, bacteria have a direct entrance into the tooth causing pulpal necrosis and periapical lysis. Teeth that are fractured with near pulp exposure without radiographic signs of periodontal disease, can often be treated with crown restoration compared to those with chronic pulp exposure that must be extracted or have root-canal therapy erformed.

Image 7B points to internal resorption, which decreases the chance of a successful root canal.

Root disease

Internal resorption

affects the pulp. The cause is unknown, but trauma and pulpal death from anachoresis (bacteria gaining access to the injured pulp through vascular channels) is believed to be contributing factors. External resorption affects the root from the outside. At times it is difficult to determine whether a lesion is due to internal or external resorption. When a normal-appearing root canal is visualized radiographically, the lesion is considered external in origin.

Image 8 notes the differences between both mandibular canals; enlarged canals indicate a "dead tooth" due to pulpal necrosis.

When examining the radiograph, the clinician should pay close attention to:

• Radiographic apical closure necessary for conventional endodontic therapy;

• Additional fractures (Image 6);

• Abnormalities in the canal, such as obstruction or internal resorption (Images 7A and 7B).

• Relative canal widths compared to adjacent or contralateral teeth. If a tooth shows an enlarged canal compared to adjacent teeth, the tooth is termed non-vital due to arrested development from pulpal necrosis (Image 8).

Image 9 shows fractured maxillary second molar showing periapical lucency.

Periapical disease is a pathologic process surrounding the apex of one or more roots that occurs as an extension of periodontal disease, or necrosis of the dental pulp from trauma or infection. Radiographic appearance of periapical disease appears as:

• Minimal to moderate alveolar bone resorption typical of a granulomatous lesion from pulpal necrosis (Image 9);

• A large homogeneous radiolucency at the apex or a dark halo in the periapical tissues caused by lysis of the bone around the tooth's apex (Image 10);

• Sharply outlined circumscribed radiolucent areas caused by a cyst (most apical cysts arise from preexisting granulomas) (see Images 11A and 11B).

• Osteomyelitis secondary to chronic endodontic disease appears as lysis of the surrounding bone (Image 8).

Image 10 finds the first molar affected by dilacerated crown and roots.

Endodontic/periodontic lesions

Sometimes endodontic and periodontic disease exist in the same tooth.

Image 11A shows feline mandibular molar with inflamed gingiva over the distal root.

Class I endoperio lesions are primary endodontic lesions that extend coronally from the root apex reaching the gingival sulcus, causing a secondary periodontal lesion. The pattern of bone loss often resembles a "J" shape with a narrow periodontal pocket at the alveolar crest (Image 12).

Image 11B shows a radicular (root) cyst of the distal root.

Class II perioendo lesions occur when the loss of attachment (periodontal disease) extends apically to a lateral canal or to the apical delta leading to pulpal necrosis. Class II perioendo lesions often affect the mandibular first molar and appear as one "floating" root without alveolar support, with a periapical endodontic lesion affecting the other tooth root (Image 13).

Image 12 shows an endoperio lesions; the pattern of bone loss often resembles a "J" shape.

Class III perioendo lesions are true combined separate endodontic and periodontal lesions, which have coalesced.

Image 13 Class II perioendo lesions often affect the mandibular first molar.