WSAVA Nov 2021 Proceedings - Flipbook - Page 18
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Techniques
DENTAL RADIOLOGY TECHNIQUES
Parallel Technique
M. Burley
The Parallel Technique can be utilised in the areas of the mouth where
the film can be positioned parallel to the root, ie mandibular premolars
and molars. The film is positioned lingually to the teeth of interest with
the margins beyond the ventral aspect of the mandible and dorsal to the
crowns of the teeth in order to image the crowns, roots and surrounding
bone structure. The xray generator is then positioned perpendicular to
the film ensuring that the area of interest is centred and fits within the
circumference of the tube head. If larger phosphor plates (sizes 4 and 5)
are being utilised, the fine focal distance may need to be increased (to a
maximum of 40cm) in order to allow for the beam’s divergence to expose
the entire plate.
Brisbane/Australia
Qualifications:
Mrs Maggie Burley
Cert IV VN, Dip VN (Dental), VTS (Dentistry), RVN
maggieburley17@gmail.com
The importance of dental radiography in the care and management of the
canine and feline patients of the small animal general practice cannot be
understated. Radiographic examination forms an integral step in the Comprehensive component of the Comprehensive Oral Health Assessment
(COHAT). Numerous studies and papers have demonstrated that dental
radiographs are almost always indicated and that they are often critical
for proper diagnosis and treatment of oral and dental disease.1
The veterinary patient presents a diagnostic challenge to the Clinician as
they often fail to show any outward sign of discomfort or pain. Our clinicians are not able to access the variety of diagnostic methods available
to dentists utilising patient feedback to assess their human patients.
Dental radiography then becomes a valuable tool for the visualisation
of subgingival structures in conjunction with the interpretation of the
patient’s history, clinical presentation, physical and periodontal examinations. Without intraoral radiography, the full extent of disease can easily
be underestimated, leading to inappropriate treatment recommendations
and failure to detect painful disease conditions.2
Producing diagnostic dental radiographs certainly provide their own challenges. They can be seen as costly, time consuming, technically difficult
and contribute to the extension of the dental procedure. However, these
challenges can be overcome by engaging in additional training in oral
anatomy, dental radiography techniques and practice.
Patient Positioning
Positioning of the patient to capture radiographic images is the preference
of the clinician. The area of interest (or arcade) is positioned uppermost
to the radiographic beam. This means the patient can be positioned in
dorsal or lateral for all mandibular images, and ventral or lateral for the
maxillary images.
Plate Positioning
Regardless of the system available, whether Dental Film, photo-stimulable
phosphor Plate or Digital Sensor (I will refer to all collectively as ‘film’),
the positioning of the film is as critical a detail as the technique chosen.
Radiographic faults will occur when the film is not positioned within the
oral cavity in order to capture the image.
Some helpful tips in positioning the plate include ensuring the bulk of the
film is within the oral cavity. This can be achieved with aligning the cusp
of the crowns on the outermost edge of the film (regardless of whether bisecting or parallel techniques are used); the film is held in place with folded gauze swabs, paper towel or similar item (care must be taken to ensure
these items are removed from the oral cavity when the radiographic exam
is concluded); a protective slip placed on sensors increasing friction will
reduce movement; the lingual frenulum can often restrict the depth the
film can be placed within the oral cavity to image the mandibular canine
roots therefore placing the tongue into its natural anatomical position, and
the film placed on the dorsal surface, can correct this.
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WSAVA GLOBAL COMMUNITY CONGRESS
Bi-secting Angle Technique
The bisecting angle technique is the most common intraoral technique
used and is the most scientifically correct way to image veterinary patients. This technique utilises the theory of equilateral triangles to create
an image that accurately represents the tooth and roots.1 It is used when
a boney structure (eg maxilla, palatine, mandibular symphysis) precludes
us from being able to place the film parallel to the tooth root.
This technique can be difficult to grasp. But let me put it into perspective for you. The bisecting angle is simply an imaginary line. It is found
halfway between the long-axis of the tooth (from cusp to apex) and the
long-axis of the film. The radiographic beam is then directed perpendicular
to the bisecting angle producing the most accurate representation of the
tooth onto the film. In essence, we are trying to cast a shadow of the tooth
(and root) onto the film that is the same length as the height of the tooth.
Think of it in terms of the sun casting a shadow of a tall tree standing in a
flat field. The sun will cast a shadow that is the same length as the height
of the tree onto the ground at certain times of the day – approximately
mid-morning, and mid-afternoon. The shadow will be shorter the higher
the sun is in the sky (towards noon), and the shadow long when the sun is
low in the sky (eg sunset). The same can be applied to the angulation of
the tube head.
Simplified Technique
The Simplified Dental Xray Technique developed by Dr Tony Woodward
uses this premise along with the approximate angles that will form
between the film and the teeth when the film is placed parallel to the hard
palate in combination with the parallel technique rather than relying on direct measurements of angles. This is not the most scientifically accurate
method, but consistently produces diagnostic images.3 There are only
three angles used in this technique – 20o, 45o and 90o.
Extra-Oral or Near-Parallel Technique
These techniques are utilised to image the maxillary premolars and molar
teeth in the cat should the clinician require good visualisation of these
teeth if obscured by the superimposition of the zygomatic arch, which
often occurs when the bisecting angle technique is used. This technique requires the patient to be positioned laterally and the film placed
extra-orally, the mouth in an open position and the beam perpendicular to
the film.
Temporomandibular Joint
Radiographic views of the TMJ are taken with the x-ray beam directed in
a DV or lateral direction through the TMJ.4 The images can be produced
using either dental film or large film placed extra-orally. The patient is
positioned in sternal recumbency with the head and neck extended for the
dorsoventral view. The lateral view is obtained with the patient positioned
in lateral recumbency with midline of the maxilla parallel to the film. In