Indications of different types of extraoral radiograph Part 2

IV. TRAUMA TO THE MANDIBLE: LOWER FACE SERIES

1. Panorex: Best single view short of a CT for viewing the mandible.
-View of choice for viewing condyles.
2. Lateral Oblique: Excellent for viewing the mandibular body and ramus.

– film-5×7 screen film usually hand held horizontally by patient.

TO VIEW BODY OF MANDIBLE


-views premolar, molar and inferior border of the mandible; broader than PA’s
-example: Body Of Left Mandible [right to left]
x-ray tube [aimed under right side of mandible]  head tilted to left
 cassette held against side of face by patient parallel to border of mandible and extending 2 cm below it [centered on 1st molar]; 65 kVp, 10 mA

TO VIEW RAMUS OF MANDIBLE

-views ramus from the angle of the mandible to the condyle; useful for ¬ /  3rds
-example: Ramus of Left mandible [right to left]
x-ray tube [aimed under right side of mandible]  head tilted to left until a line from the right angle of the mandible to the left condyle is parallel to the deck
 protrude the mandible. This keeps the spine out of the view.
 cassette held against side of face [ramus] by patient and extending 2 cm below the inferior border of the mandible; 65 kVp, 10 mA

 

3. Towne’s: (anterior-posterior projection)
. -AP view w/ 30 tilt of the tube caudally
-view can be used to observe condyles, necks, rami and mandibular symphysis.
-also visualized: occipital bone, foramen magnum, dorsum sellae and petrous ridges.
-cassette held by a holding device vertically.

 

4. Reverse Towne’s: (Modified Towne’s)

Positioning of the patient to take a Reverse Towne's radiograph

-Posterior-Anterior view, mouth open
-View can be used to observe fractures involving the condylar neck, and also when displacement of the condyle is suspected
-good visualization of the posterolateral wall of the maxillary antrum.
-cassette held by a holding device vertically.
-example: head is centered in front of film with the canthomeatal line projected 25 -30 downward; beam goes through the occipital bone; 75-80 kVp.
5. Posterior-Anterior: View used to observe the mandibular angle and body.

V. OTHER VIEWS CONSIDERED BY DENTAL

1. TMJ VIEWS

Transpharygeal Projection

– film-5×7 screen film [usually held vertically] hand held by patient
– provides an excellent “scout” view of gross changes on the condylar surfaces
– example for taking a radiograph on the left TMJ, patient’s midsagittal plane should be perpendicular to deck.
 rotate head 7 -10 away from the cassette [moves opposite condyle out of the way]
 cassette held against ear and cheekbone on left side of face by patient. The mouth can be opened or closed.
 x-ray tube directed -5 , beneath the zygomatic arch on right.

Transorbital Projection

– cassette held by a holding device vertically [cephalostat]
– frontal radiograph
– medial and lateral aspect of condyle, the neck, the eminence and sometimes the zygomatic arch.
– example for left TMJ
patient is seated with midsagittal plane perpendicular to deck and Frankfort plane parallel to the deck.
 cassette is placed behind the left TMJ  turn head 20 to the left
 x-ray tube directed +35 , from the front through the floor of the left orbit and left TMJ

Transcranial Projection

– film-5×7 screen film [usually held vertically] and is hand held by patient
– provides a view down the long axis of the condyle and the relationship of the condyle to the fossa
– example for left TMJ – patient’s midsagittal plane perpendicular to deck
 cassette held against ear and cheekbone on left side of face by patient
 x-ray tube [directed +25,1/2″ behind and 2″ above the right external auditory meatus

2. PANOREX


– Correctly called a pantomograph or a panoramic radiograph; Panorex the brand name of the first panoramic machine introduced to North America by the S.S. White Co. in 1959.
– The area where the images are sharp is a 3D horseshoe shaped zone called the focal trough, image layer, zone of sharpness, central image layer; therefore, correct patient positioning is critical.
– Frankfort plane parallel to the deck, the midsagittal plane, perpendicular to the deck, and the teeth in the focal trough.
– Real image – object lies between the center of rotation and the film.
– Ghost image – object lies between the x-ray source and the center of rotation.

ERROR

RESULT

Chin too low exaggerated smile line; loss of ¯ ant. apices; loss of condyles
Tongue not raised black area over ­ apices
Patient slumped superimposition of ghost image of spine
Head tilted to left causes left to be higher on film
Head rotated to left causes left to be magnified and right to be narrow
Lips open black space between ­ the upper and lower lips
Too far forward narrow ant. teeth; superimposition of spine on mand.
Too far back wide ant. teeth; loss of apices
Chin too high reverse smile line; hard palate superimposed on apices; condyles lost on side

VI. Helpful Hints for Reading Extraoral Films – Facial fractures

  1. Radiographic examination should document fractures from two different angles.
  2. Know the most common patterns of facial fractures.
  3. Look for bilateral symmetry.
  4. 6O-70% of all facial fractures involve the orbit.

VII. SUMMARY

In an operational environment, the comprehensive dentist should be familiar with the four basic medical views: Waters, Posterior-Anterior, Lateral, and the Submentovertex for evaluating facial trauma.

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