Interpretation of dental radiographs (Proceedings)

Radiographs produced without distortion are of great use in dentistry and are far easier to interpret than those with superimposed, foreshortened or elongated images. Whole books have been devoted to this very involved subject, but only the most pertinent points will be broached here

During radiographic diagnosis it should be remembered that many anatomic structures may appear to be pathological, and radiographic diagnosis alone is not possible. An accurate history should be taken to correlate clinical findings with radiographic findings. For example many anatomic structures and other osteolytic lesions may appear similar to endodontic lesions. Clinical evaluation should include a history of swelling if present, fistula formation, tooth crown color, of coronal appearance that reflects lack of tooth vitality. Palpate over the apex to determine swelling and percussion along the long axis to check for hypersensitivity.

A review of radiographic techniques to produce radiographs of good diagnostic quality for accurate interpretation, and a complete knowledge of radiographic landmarks are essential in making a good radiographic diagnosis.

Lamina dura

A valuable landmark to radiographic diagnosis is the lamina dura, also referred to as bundle bone. Lamina dura is a compact layer of bone lining the alveolus. It appears as a thin white line adjacent to the periodontal ligament. Indications of pulpal necrosis can often be seen as abnormalities in the shape and continuity of the lamina dura, and width and shape of the periodontal ligament. Also a widening of the periodontal ligament often suggests periodontal involvement. Advanced endodontic disease produces chemotoxic exudates and bacterial antigens of an infected pulp exit the apex, they effect change in the periodontal ligament and the lamina dura that are evident radiographically. The presence or of the lamina dura is determined by the shape and position of the tooth and root in relation to the x-ray beam. The x-rays passing through a socket that tends to be oblong in shape must pass through many times the width of the adjacent alveolus and are attenuated by the greater thickness of bone, producing a whit line. Although changes in the lamina dura can be significant, they must be tempered by an understanding of the factors in the result in the radiographic visualization of the lamina dura. Various radiographic angles can show or fault to show radiographically evident pathology. Foreshortening of the tooth's image, by poor vertical placement of the tube head, can result in failure to show periapical lysis, or periodontal bone loss. Pathology can be hidden by poor radiographic technique.

Apical Rarefaction

A lytic halo at or around the apex of a tooth root, usually suggests pulpal pathology. After endodontic involvement the periapical lesion may take months to appear. However is important to note that not all endodontically involved teeth show periapical lysis. Also the appearance of a lytic area at the apex of a lower canine tooth in dogs may be miss diagnosed through improper x-ray alignment. The mental foremen are just posterior to the canine apex. A central beam directed from rostral to caudal instead of at right angles to the canine, will radiographically place the mental foremen at the apex of the canine.

Differential Diagnosis:

Endodontic involvement. with pulpal pathology extending into the periapical bone. Periodontal disease, such as fistulas tracts extending to the apex through the periodontal tissues, (there will usually be additional evidence of periodontal disease. e.g. horizontal or vertical bone loss). Absence of lamina dura with clinical evidence of combination periodontal endodontic pathology; Periradicular cyst; with evidence of a cystic membrane and almost total bone loss within the cyst.

Comparison should always be made with other teeth of the same type in the same patient. The periapical bone of the canine teeth of normal dogs often appears radiolucent. A distinctly round radiolucent area however, is usually pathological.

Alveolar Bone Loss

The degree of' periodontal disease can be more accurately assessed with the aid of intra-oral radiography.

Horizontal bone loss without bony pocket formation. and vertical bone loss with infra-bony pocket formation are easily visible. Once accurately diagnosed. appropriate treatment can be provided.

Fractures

Root fracture.

Horizontal root fracture at or near the apical one third of the root rarely need therapy. The apical segment retains its blood supply, and the incisal segment often receives collateral circulation. Transverse root fractures usually result in displacement of the segments. Long axis fractures and transverse fractures rarely can be salvaged. Mandibular fractures are often associated with tooth roots. Fractures is line with tooth roots require special considerations.

Retained Root Tips

Roots are frequently left in their alveolar sockets. Retained root segments may be the result of trauma, coronal resorbtion with segments of root retention commonly seen in cats are usually the result of coronal fracture while extrating the tooth. Radiology is invaluable in the detection and location of these otherwise invisible roots which can be seen as more radio dense areas within the alveolar bone. There are four possible results of fractured retained root fractures. Root tips can be resorbed , migrate out of the socket, become encapsulated in bone without complications, or form a sequeli and require subsequent removal.

Caries

Teeth with dental decay or resorptive lesions should be always be radiographed to determine the extent of the lesion before selection of the appropriate treatment.

Detection of unerupted or missing permanent teeth

The absence of permanent teeth/tooth after the normal time of eruption should be radiographed to confirm a genetically missing tooth, an impacted tooth, of dental follicular involvement that can delay eruption. A series of radiographs may be necessary to reveal the presence of dentition or pathology. Missing permanent teeth are often ether faults or disqualifications in confirmation competition. Missing permanent teeth can be detected radiographically before irruption, between nine and twelve months. This can be of great assistance in certification of complete dentition before selling show puppies where missing teeth is a fault or disqualification.

Neoplasia

Differential diagnosis of neoplastic lesions is greatly enhanced with radiology. The extent of bony involvement, bony lysis, or inclusions provides the clinician with invaluable diagnostic information.