Mandible lateral oblique

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Lateral Oblique of the Mandible and Maxilla Amila Abeyweera

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Transcript of Mandible lateral oblique

  • Lateral Oblique of the Mandible and Maxilla

    Amila Abeyweera

  • Introduction

    The lateral oblique radiograph is an extra-oral projection produced using conventional intra-oral X-ray equipment that reveals a larger area of the jaws than intra-oral radiography. It can also be produced using a skull unit.

  • Indications

    Assessment of the presence/absence of teeth and also the position of un-erupted teeth (especially third molars).

    Detection and assessment of fractures of the mandible.

    Assessment of large pathological lesions (e.g. cysts, tumours, osteodystrophies).

    When intra-oral radiography is impossible (e.g. trismus, severe gagging).

    Patients with physical and/or medical conditions in which large coverage and a rapid imaging technique is needed.

  • General imaging principles

    The head is rotated to ensure that the area under examination is parallel to the film.

    The film and the median plane are not parallel.

    To avoid superimposition of the opposite side of the jaws, the combined angulation of the angle between the median plane and the film plus the angulation of the X-ray beam must not be less than 20 degrees.

    The central ray is perpendicular to the film but oblique to the median plane.

  • Position of Patient and Cassette

    The patient sits comfortably, with the head supported. The median plane is vertical.

    A 13 * 18-cm cassette is used with a removable film marker attached to designate the side of the mandible to be imaged.

    The cassette is positioned against the patients cheek overlying the region of the mandible under investigation, with the lower border parallel to the inferior border of the mandible but lying at least 2cm below it.

    The positioning achieves a 10-degree angle of separation between the median sagittal plane and the film.

    The patient is instructed to stabilize the cassette in this position.

  • The patients head is rotated to the side of interest. This positions the contralateral ascending ramus forwards and increases the area between the neck and the shoulder to provide space for the X-ray tube.

    The chin is raised slightly to increase the space between the posterior aspect of the mandible and the cervical spine.

    The patient is asked to protrude the mandible.

  • Cassette and the X-ray tube positions for a right lateral oblique radiograph of the body of the mandible and maxilla. Note the rotation

    of the head with flattening of the nose against the cassette

  • Direction and centring of the X-ray beam Direct the central ray at a point 2cm below and behind the angle of the

    contralateral side of the mandible (see figure).

    Positioning of the tube is dependent upon the area of clinical interest, o Third molar region for assessment of the position of third molars and possible

    pathology in this region

    o Premolar region for assessment of the developing dentition

    o Lower canine region if there is evidence of mandibular fracture or other pathology.

    The choice of beam angulation varies between 10 degrees upward and 10 degrees downward .

    The central ray is perpendicular to the plane of the film.

  • Schematic to illustrate the direction of the beam for a lateral oblique radiograph of the body of the

    mandible and maxilla

  • Lateral oblique radiograph of the body of the mandible and maxilla

  • Modifications

  • The choice of a downward beam angulation is related to the (clinical) need to avoid superimposition of the hyoid bone on the body of the mandible.

    To image the maxillary and mandibular canine/incisor region requires further rotation of the head to a point where the patients nose is flattened against the cassette.

    It is important to ensure that the area of interest is parallel to the film. This technique reduces the angle of separation between the median sagittal plane and the film to five degrees.

  • Lateral oblique of the ramus of the mandible

    This projection gives an image of the ramus from the angle of the mandible to the condyle.

  • Position of patient and cassette

    The patient sits comfortably, with the head supported. The median plane is vertical.

    A 13 * 18-cm cassette is used with a removable film marker attached to designate the side of the mandible to be imaged.

    The cassette is positioned against the patients cheek overlying the ascending ramus and the posterior aspect of the condyle of the mandible under investigation.

    The cassette is positioned so that its lower border is parallel with the inferior border of the mandible but lies at least 2cm below it.

    The positioning achieves a 10-degree angle of separation between the median sagittal plane and the film.

  • The patient is instructed to support the cassette in this position.

    The mandible is extended as far as possible.

    Limit rotation of head (~ 10 degrees) towards the cassette.

  • Direction and centring of the X-ray beam The central ray is directed posteriorly with upward angulation

    (cephalad) of 10 degrees towards the centre of the ramus of the mandible on the side of interest.

    The centring position of the tube is the contralateral side of the mandible at a point 2cm below the inferior border in the region of the first/second permanent molar.

  • Cassette and the X-ray tube positions for a right lateral oblique radiograph of the ramus of the mandible

  • Essential image characteristics

    There should be no removable metallic foreign bodies.

    There should be no motion artefacts.

    There should be no antero-posterior positioning errors.

    There should be no evidence of excessive elongation.

    There should be no evidence of incorrect horizontal angulation.

    There should be minimal superimposition of the hyoid bone on the region of (clinical) interest.

    There should be good density and adequate contrast between the enamel and the dentine.

    There should be no pressure marks on the film and no emulsion scratches.

  • There should be no roller marks (automatic processing only).

    There should be no evidence of film fog.

    There should be no chemical streaks/splashes/contamination.

    There should be no evidence of inadequate fixation/washing.

    The name/date/left or right marker should be legible.

  • Modifications

  • Patient - Supine

    Patient supine on the X-ray couch.

    Use a 10-degree wedge-shaped foam pad to achieve separation of one side of the mandible from the other.

    Attach a removable film marker to the cassette to designate the side of the mandible to be imaged.

    With the cassette on the pad, the patients head is rotated so the side of the jaw to be examined is parallel to the film, with the median sagittal plane parallel to the cassette.

    The head is tilted back on the spine to achieve further extension of the contralateral mandible away from the region of interest.

  • Direction and centring of the X-ray beam The central ray is angled 30 degrees cranially at an angle of 60

    degrees to the cassette and is centred 5cm inferior to the angle of the mandible remote from the cassette.

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    Patient lying supine on the X-ray couch and positioned for a right lateral

  • Using an angle board

  • Position of patient and cassette

    The head is positioned parallel to the angle board and cassette, but with the sagittal plane inclined to the vertical by the degree of angulation set by the device.

    Some angle boards incorporate ear rods to ensure accurate localization of the patient.

    A small forward tilt of the chin avoids superimposition of the cervical vertebrae on the ramus.

  • Direction and centring of the X-ray beam The tube is positioned below the angle of the mandible, remote from

    the film, and the central ray is directed towards the vertex.

    To avoid superimposition of the opposite side of the face, there must be an effective separation of 20 degrees.

    For example, with a sagittal plane angled at 15 degrees by the angle board, the central ray must be angled five degrees to the vertex to achieve the required separation of 20 degrees.

  • Reference

    Clarks Positioning in Radiography 12th Edition

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