Panoramic Tomography

DENTAL RADIOGRAPHY and Examination of Mandible

Pathology Demonstrated:

• Fractures and infectious processes of the mandible and dental structures are shown.
• Used as an adjuvant for pre-bone marrow transplants.

Technical Factors:

• IR size - 23 x 30 cm (9 x 12 inches), crosswise 
• Curved non-grid cassette 
• 70 to 80 kV range 
• Panoramic and Dental Radiography Unit Preparation:
• Attach image receptor to panoramic unit.
• Position tube and image receptor at standing position.
• Raise chin rest to approximately same level as patient's chin.

Shielding:

• Wrap vest type lead apron around patient.

Patient Position:

• Remove all metal, plastic, and other removable objects from head and neck.
• Explain to patient how tube and image receptor rotate and the time span needed for exposure.
• Guide patient into unit, resting patient's chin on bite block.
• Position patient's body, head and neck. Do not allow head and neck to stretch forward, but have patient stand in close, with spine straight and hips forward.

Part Position:

• Adjust height of chin rest until Intra-Orbital Meatal Line (IOML) is aligned parallel with floor.
• The occlusal plane (plane of biting surface of teeth) declines 10° from posterior to anterior.
• Align MSP with the vertical center line of the chin rest.
• Position bite block between patient's front teeth. see note.
• Instruct patient to place lips together and position tongue on roof of mouth.

Central Ray:

• X-ray beam direction is fixed and directed slightly cephalic to project anatomic structures, positioned at the same height, on top of one another.
• Fixed SID, per panoramic unit.

Collimation:

• A narrow, vertical-slit diaphragm is attached to tube, providing collimation.
• Note: When the TJMs are of interest, a second panoramic image is taken with the mouth open.
• This requires placement of a larger bite block between the patient's teeth.

Radiographic Criteria:
Structure Shown:

• A single image of the teeth, mandible, TMJs, nasal fossae, maxillary sinus, zygomatic arches, and maxillae is shown.
• A portion of the cervical spine is visualized.

Position of Patient in Dental Radiography:

• The mandible visualized without rotation or tilting is indicated by the following:
• TMJs on the same horizontal plane in the image.
• Rami and posterior teeth equally magnified on each side of the image.
• Anterior and posterior teeth sharply visualized with uniform magnification.

Correct Patient Position is indicated by the following:

• Mandibular symphysis projected slightly below the mandibular angles
• Mandible oval shape
• Occlusal plane is parallel with long axis of the image
• Upper and lower teeth positioned slightly apart with no superimposition
• Cervical spine demonstrated with no superimposition of the TMJs.

Collimation and Central ray:

• The mandible is located at the center of the image
• The entire mandible in included in the collimation field.

Exposure Criteria:

• Density of mandible and teeth is uniform across entire image.
• No density loss is evident at the center.
• No artifacts are superimposed on the image