The bisecting angle technique has been the technique of choice for most intraoral radiographic techniques. This is especially
true for maxillary exposures. The limited intra oral 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 intra oral 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 intra oral 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 intra oral 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. Intra oral 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.