Dental radiography: Digital techniques and radiographic diagnosis (Proceedings)

The bisecting angle technique has been the technique of choice for most intraoral radiographic techniques. This is especially true for maxillary exposures. The limited intraoral confines of the maxilla, lower incisors and canine teeth have made this technique the method of choice. However the resultant radiographs often left much to be desired. Elongation or foreshortening of the teeth is a common finding, making accurate diagnosis very difficult.

Lower posterior dentition exposures are normally performed with parallel techniques. Parallel radiographs provide very accurate films for diagnosis.

Because of the irregularities in the make-up of the oral tissues, intra oral film cannot always be place parallel to the teeth being radiographed as normally performed when radio graphing long bones. The most difficult exposure to obtain with a degree of accuracy is an upper fourth premolar exposure. This difficulty is exacerbated by the bisecting angle technique. A near parallel exposure can be taken for the upper fourth premolar.

A near parallel technique for upper posterior dentition will be described. The measurements will be presented for the average size mesaticephalic head (example: Border Collie). However the same principals apply for all head sizes and types. Only the oral opening measurements for larger or smaller heads are slightly changed.

The crown of the upper premolar is near perpendicular to the horizontal. However the roots diverge medially approximately 12 to 15 degrees. This divergence aids in the near parallel exposure technique.

With the dog in a lateral recumbence, a 3 cc syringe cover is reduced, (cap end) to approximately 6 cm. in length. The plastic cover provides a stable mouth gag while allowing radiographic rays to pass through without distortion. Also it is much easier to roll the patient without gag dislodgement as encountered with spring-loaded devises.

The plastic sleeve is positioned between the upper and lower canine teeth producing an approximate 6cm opening from upper incisal edge to lower incisal edge.

A size 4 intraoral film is placed in the mouth so that one side of the film buts up against the palatal occlusal margin opposite the side to be radiographed. The opposite edge of the film is of the bent, and a slight portion of the film is tucked behind the large occlusal cusp of the lower first molar on the side to be radiographed. The lower molar hook, acts as a retainer for the final film position. Intraoral film can be bent or shaped to a degree to accommodate these confines. This in effect results in approximately a 2cm space between the film and the palatal surface. The upper portion of the film is now near parallel to the root morphology of the upper fourth premolar. The x-ray tube head is positioned so that the central beam passes at right angles to the upper portion the intra oral film and the tube head is parallel to the muzzle. The resultant exposure will produce a near parallel view of the root morphology.

The same procedure can be applied for upper and lower canine teeth with the same parallel result.

An intraoral size 4 film is positioned so that the back edge of the film is just anterior to the fourth premolar. The anterior edge of the film is tipped to the degree that places the canine tooth and the intraoral film parallel to each other. The film must be positioned far enough into the mouth so as not to miss the apex of the canine tooth. Again, the tube head is placed so that the central beam is at right angles to the film and the canine tooth. This exposure will produce a near parallel image of the incisors as well.

This technique works equally well for small doge and cats, only changing the film size. Intraoral film can be stabilized or propped up to the desired position and angle with either gauze sponges or wet rolled up pieces of paper towel.

Digital radiographic

Both the bisecting angle and near parallel techniques can be used with digital radiographic techniques.

The advantages of digital imaging

• Instant image capture

• Better communications between peers

• Easier image storage and retrieval

• Reduced radiation levels to patients and techs

• Manipulation of images for better diagnosis and care

• High resolution for diagnostic images

• Smart sensor electronics.

• USB connectivity. Highest value. Perfect for multiple operatory offices. Complete networking.

• Software stands alone or integrates.

There are some disadvantages to digital radiographic techniques, however minimal. First, the sensor is inflexible as compared to conventional x-rays which can be bent to a degree to accommodate the shallow confines if the dog and cat mouth. Also, the supplied sensor cannot be bent and can be too large for some oral areas. Additionally, the digital sensor comes only in size 2. There are times when the larger film size 4 is needed for larger dog mouths. There are times when conventional x-ray film is needed, such as the use of a flexible size four film to capture an entire posterior quadrant.

The advantages of digital radiography far outweigh the disadvantages. It behooves the practitioner to take advantage of this advancement in dental radiography.

Interpretation of dental radiographs

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, and 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 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 misdiagnosed 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 intraoral 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 fractures 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 extracting the tooth. Radiology is invaluable in the detection and location of these otherwise invisible roots that 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.