Occlusal Radiography

Occlusal radiography is defined as those intraoral radiographic techniques taken using a dental X-ray set where the film packet (5.7 x 7.6 cm) or a small intraoral cassette is placed in the occlusal plane.

Maxillary occlusal projections Upper standard occlusal (standard occlusal) Upper oblique occlusal (oblique occlusal) Vertex occlusal (vertex occlusal). Mandibular occlusal projections Lower 90° occlusal (true occlusal) Lower 45 ° occlusal (standard occlusal) Lower oblique occlusal (oblique occlusal).

Upper standard occlusal This projection shows the anterior part of the maxilla and the upper anterior teeth. Main clinical indications Periapical assessment of the upper anterior teeth, especially in children but also in adults unable to tolerate periapical films Detecting the presence of unerupted canines, supernumeraries and odontomes As the midline view, when using the parallax method for determining the bucco/palatal position of unerupted canines Evaluation of the size and extent of lesions such as cysts or tumours in the anterior maxilla Assessment of fractures of the anterior teeth and alveolar bone. It is especially useful in children following trauma because film placement is straightforward.

Technique and positioning 1.The patient is seated with the head supported and with the occlusal plane horizontal and parallel to the floor and is asked to support a protective thyroid shield. 2. The film packet, with the white (pebbly) surface facing uppermost, is placed flat into the mouth on to the occlusal surfaces of the lower teeth. The patient is asked to bite together gently. The film packet is placed centrally in the mouth with its long axis crossways in adults and anteroposteriorly in children.

3. The X-ray tubehead is positioned above the patient in the midline, aiming downwards through the bridge of the nose at an angle of 65°- 70° to the film packet (see Fig. 10.1).

A.Diagram showing the position of the film packet in relation to the lower arch. B.Positioning from the front; note the use of the protective thyroid shield. C.Positioning from the side. D.Diagram showing the positioning from the side.

An example of an upper standard occlusal radiograph with the main radiographic features indicated.

Upper oblique occlusal This projection shows the posterior part of the maxilla and the upper posterior teeth on one side. Main clinical indications Periapical assessment of the upper posterior teeth, especially in adults unable to tolerate periapical films Evaluation of the size and extent of lesions such as cysts, tumours or osteodystrophies affecting the posterior maxilla Assessment of the condition of the antral floor As an aid to determining the position of roots displaced inadvertently into the antrum(cavity) during attempted extraction of upper posterior teeth Assessment of fractures of the posterior teeth and associated alveolar bone including the tuberosity.

Technique and positioning 1.The patient is seated with the head supported and with the occlusal plane horizontal and parallel to the floor. 2. The film packet, with the white (pebbly) surface facing uppermost, is inserted into the mouth on to the occlusal surfaces of the lower teeth, with its long axis anteroposteriorly. It is placed to the side of the mouth under investigation, and the patient is asked to bite together gently. 3. The X-ray tube head is positioned to the side of the patient's face, aiming downwards through the cheek at an angle of 65°-70° to the film, centring on the region of interest (see Fig. 10.3). Note: If the X-ray tubehead is positioned too far posteriorly, the shadow cast by the body of the zygoma will obscure the posterior teeth.

A. Diagram showing the position of the film packet in relation to the lower arch for a LEFT upper oblique occlusal. B. Positioning for the LEFT upper oblique occlusal from the front; note the use of the protective thyroid shield. C. Diagram showing the positioning from the front.

An example of an upper left oblique occlusal radiograph with the main radiographic features indicated.

Vertex occlusal This projection shows a plan view of the tooth bearing portion of the maxilla from above. To obtain this view the X-ray beam has to pass through a considerable amount of tissue, delivering a large dose of radiation to the patient. An intraoral cassette containing intensifying screens is used for this projection to reduce the dose. Main clinical indication Assessment of the bucco/palatal position of unerupted canines.

Technique and positioning 1.The patient is seated with the head supported and with the occlusal plane horizontal and parallel to the floor. 2. The cassette is placed inside a small plastic bag to prevent salivary contamination and crossinfection. 3. It is then inserted into the mouth on to the occlusal surfaces of the lower teeth, with its long axis anteroposteriorly and the patient is asked to bite on to it

4. The X-ray tube head is positioned above the patient, in the midline, aiming downwards through the vertex of the skull. The main beam is therefore aimed approximately down the long axis of the root canals of the upper incisor teeth (see Fig. 10.5).

A. Diagram showing the position of the cassette in relation to the lower arch. B. Positioning for the vertex occlusal from the front; note the use of the protective thyroid shield. C. Positioning from the side. D. Diagram showing the positioning from the side.

Disadvantages There is a lack of detail and contrast on the film because of the intensifying screens, the mass of tissue the X-ray beam has to penetrate and the consequent scatter. The primary X-ray beam may be in direct line with the reproductive organs. A relatively long exposure time is needed (about 1 second) despite the use of intensifying screens. There is direct radiation to the pituitary gland and the lens of the eye. If the X-ray beam is positioned too far anteriorly, superimposition of the shadow of the frontal bones may obscure the anterior part of the maxilla.

An example of a vertex occlusal radiograph with the main radiographic features indicated.

Lower 90° occlusal This projection shows a plan view of the tooth bearing portion of the mandible and the floor of the mouth.

Main clinical indications Detection of the presence and position of radiopaque calculi in the submandibular salivary ducts Assessment of the bucco-lingual position of unerupted mandibular teeth Evaluation of the bucco-lingual expansion of the body of the mandible by cysts, tumours or osteodystrophies Assessment of displacement fractures of the anterior body of the mandible in the horizontal plane.

Technique and positioning 1.The film packet, with the white (pebbly) surface facing downwards, is placed centrally into the mouth, on to the occlusal surfaces of the lower teeth, with its long axis crossways. 2.The patient is asked to bite together gently. 3.The patient then leans forwards and then tips the head backwards as far as is comfortable, where it is supported. 4.The X-ray tubehead, with circular collimator fitted, is placed below the patient's chin, in the midline, centring on an imaginary line joining the first molars, at an angle of 90° to the film

Lower 90° occlusal

An example of a lower 90° occlusal radiograph with the main radiographic features indicated

Lower 45° occlusal This projection is taken to show the lower anterior teeth and the anterior part of the mandible. The resultant radiograph resembles a large bisected angle technique periapical of this region. Main clinical indications Periapical assessment of the lower incisor teeth, especially useful in adults and children unable to tolerate periapical films Evaluation of the size and extent of lesions such as cysts or tumours affecting the anterior part of the mandible Assessment of displacement fractures of the anterior mandible in the vertical plane.

Technique and positioning 1.The patient is seated with the head supported and with the occlusal plane horizontal and parallel to the floor. 2. The film packet, with the white (pebbly) surface facing downwards, is placed centrally into the mouth, on to the occlusal surfaces of the lower teeth, with its long axis anteroposteriorly, and the patient is asked to bite gently together. 3. The X-ray tubehead is positioned in the midline, centring through the chin point, at an angle of 45° to the film (see Fig. 10.9).

A. Diagram showing the position of the film packet (white pebbly surface facing downwards) in relation to the lower arch B. Positioning for the lower 45° occlusal from the side. C. Diagram showing the positioning from the side.

An example of a lower 45° occlusal radiograph with the main radiographic features indicated.

Lower oblique occlusal This projection is designed to allow the image of the submandibular salivary gland, on the side of interest, to be projected on to the film. However, because the X-ray beam is oblique, all the anatomical tissues shown are distorted. Main indications Detection of radiopaque calculi(calcium) in a submandibular salivary gland Assessment of the bucco-lingual position of unerupted lower wisdom teeth Evaluation of the extent and expansion of cysts, tumours or osteodystrophies in the posterior part of the body and angle of the mandible.

Technique and positioning 1. The film packet, with the white (pebbly) surface facing downwards, is inserted into the mouth, on to the occlusal surfaces of the lower teeth, over to the side under investigation, with its long axis anteroposteriorly. The patient is asked to bite together gently. 2. The patient's head is supported, then rotated away from the side under investigation and the chin is raised. This rotated positioning allows the subsequent positioning of the X-ray tubehead. 3. The X-ray tubehead with circular collimator is aimed upwards and forwards towards the film, from below and behind the angle of the mandible and parallel to the lingual surface of the mandible (see Fig ). Note: The lower oblique occlusal is also mounted with the embossed dot pointing away from the examiner.

A. Diagram showing the position of the film packet (white pebbly surface facing downwards) in relation to the lower arch for the LEFT lower oblique occlusal. B. Positioning for the LEFT lower oblique occlusal from the side. C. Diagram showing the positioning from the side and indicating that the patient's chin is raised and that the head is rotated AWAY from the side under investigation.