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Extraoral Radiographs - Lecture Notes | DEA 131, Exams of Health sciences

Front Range Community CollegeHealth sciences

Material Type: Exam; Class: Advanced Dental Radiography; Subject: Dental Assisting; University: Front Range Community College; Term: Unknown 1989;

Typology: Exams

Pre 2010

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DEA 131
RADIOLOGY II
EXTRAORAL RADIOGRAPHS
OBJECTIVES:
At the completion of this lesson, the student will with at least 70% on a written and/or
oral exam:
1. Describe the purpose and use of extraoral radiographs
2. Identify the types of film used in extraoral radiography
3. Give three reasons for making extraoral exposures
4. Identify the types of projections that can be performed extraorally
5. State the purpose and describe the procedure for each extraoral projection
6. Define key words.
EXTRAORAL RADIOGRAPHS
An examination made of the head and facial region using films located outside the mouth
DEFINITION
A radiograph exposed outside the mouth allowing the dentist to exam areas not fully
covered by intraoral films or to visualize the skull and facial structures
PURPOSE
To exam structures of the skull, the maxilla and mandible and the TMJ
Used to:
–Examine large areas of the jaws and skull
–Study growth and development of bone and teeth
–Detect fractures and evaluate trauma
–Detect pathological lesions and diseases of the jaw
–Detect and evaluate impacted teeth.
–Evaluate TMJ disorders
MAJOR USERS OF EXTRAORAL RADIOGRAPHICS
Orthodontist—used to measure bone growth and development of the bones and
the teeth.
Prosthodontists—to recorded the contour of the lips and face the relationship of
teeth before removal
Oral Surgeons—to evaluate trauma, to determine the location and extent of
fractures to locate impacted teeth, abnormalities and malignancies, and injuries to
the TMJ
FILM SIZE
No definite rule governs extraoral film size
Usual sizes include; 5 x7 inch or 8 x 10 inch
pf3
pf4
pf5

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DEA 131

RADIOLOGY II

EXTRAORAL RADIOGRAPHS

OBJECTIVES:

At the completion of this lesson, the student will with at least 70% on a written and/or oral exam:

  1. Describe the purpose and use of extraoral radiographs
  2. Identify the types of film used in extraoral radiography
  3. Give three reasons for making extraoral exposures
  4. Identify the types of projections that can be performed extraorally
  5. State the purpose and describe the procedure for each extraoral projection
  6. Define key words. EXTRAORAL RADIOGRAPHS An examination made of the head and facial region using films located outside the mouth DEFINITION A radiograph exposed outside the mouth allowing the dentist to exam areas not fully covered by intraoral films or to visualize the skull and facial structures PURPOSE  To exam structures of the skull, the maxilla and mandible and the TMJ  Used to:
  • Examine large areas of the jaws and skull
  • Study growth and development of bone and teeth
  • Detect fractures and evaluate trauma
  • Detect pathological lesions and diseases of the jaw
  • Detect and evaluate impacted teeth.
  • Evaluate TMJ disorders MAJOR USERS OF EXTRAORAL RADIOGRAPHICS  Orthodontist—used to measure bone growth and development of the bones and the teeth.  Prosthodontists—to recorded the contour of the lips and face the relationship of teeth before removal  Oral Surgeons—to evaluate trauma, to determine the location and extent of fractures to locate impacted teeth, abnormalities and malignancies, and injuries to the TMJ FILM SIZE  No definite rule governs extraoral film size  Usual sizes include; 5 x7 inch or 8 x 10 inch

PATIENT PREPARATION

 SEAT THE PATIENT

 EXPLAIN THE PROCEDURE TO THE PATIENT

 ADJUST THE CHAIR TO A COMFORTABLE WORKING LEVEL

 IF POSSIBLE PLACE THE LEAD APRON

 REMOVE EYEGLASSES AND METAL OBJECTS FOR IN AND AROUND

THE MOUTH.

RADIOGRAPHIC TECHNIQUES

 Lateral jaw projection  Also know as the lateral oblique projection  The most frequent extraoral radiograph made with the conventional radiograph machine  Have been largely replaced by the panoramic radiograph.  Purpose  To examine the posterior region of the mandible.  Especially valuable to use with children, patients with fractures or trismis or are too young or senile to hold intraoral films.  Made to evaluate the conditions of the bone and to locate impacted teeth or large lesions.  Film Placement  Cassette is positioned flat against the cheek and centered over the mandibular first molar area  Edge of cassette should protrude slightly beyond the tip of the nose and the chin.  Patient holds the cassette tightly against the cheek with the palm of one hand the thumb of is placed under the lower edge of the cassette.  Head Position  Tilted toward the side to be examined  Chin is protruded   Central Ray Alignment  Directed toward the first molar region of the mandible from a point slightly underneath the opposite side of the mandible  Directed as close to the perpendicular to the horizontal plane of the film as possible  Exposure Factors  Depending upon the screen-film combination, the target-film distance and the equipment used.  Four possible areas of concern can be shown  To change the center of interest  Vary the angle at which the film is held against the face and the direction of the central ray  The central ray is directed perpendicularly to the desired area, usually at the level of the occlusal plane.

 Tomography  Transcranial Projection  Purpose  To view the TMJ in both the open and closed positions  Film Placement  Cassette is positioned against the ear and centered over the acoustic meatus.  The cassette is covered with lead except for where the view is to be made on the cassette.  Head Position  The midsagittal plane of the patient’s head is positioned perpendicular to the floor and parallel to the cassette.  Central Ray Alignment  The central ray is directed at a vertical angulation of about +25 degree to the center of the part of the film that is not covered with lead. PANORAMIC RADIOGRAPHY  A technique for producing a radiograph that shows both the maxilla and mandible on a single radiograph.  Purpose  To provide a radiograph with an image of the maxilla and mandible on a single film.  Uses  Examine large areas of the face and jaw  Locate impacted teeth  Evaluate trauma, lesions and diseases of the jaw  Evaluate growth and development  How the machine works  Based on the theory of rotational panoramic radiography. Defined as a technique for making radiographic projections by utilizing a narrow beam of radiation to image a curved layer.  The patient is stationary while the film and radiation move continuously. This principle is called the curved surface laminography.  The cassette and the tube head move in opposite directions while the patient stands or sits still.  The rotational center is defined as the axis on which the tube head and the cassette rotate is the functional focus of the projection.  The radiation emerges from a narrow vertical slit opening in the tube head and are constricted to form a narrow band.  The narrow opening in the tube head, the radiation beam is collimated and much less radiation passes through the patient to the slit in the cassette.  Depending on the manufacturer the number of rotational centers vary  Three basic types of rotational centers  Double-centered—the left and right sides of the arc formed by the teeth and jaws coincide with the arcs of the two circles with centers at “X” and “O”. Two separate exposures are necessary resulting in a split image.

 Triple-centered—three centers of rotation are used. Three separate segments yet the radiation can be shifted form one center to the other with minor interruptions  Moving-centered—good diagnostic results can be obtained with this type of machine. The beam rotates around a center that moves continuously in a path that is similar in shape to the anatomy being examine. Both horizontal and vertical magnification of the image are relatively constant. Concept of the Focal Trough  A theoretical concept used in rotational panoramic radiograph to determine where the dental arches, the sinuses or other areas that are to be examined should be positioned in order to achieve the clearest image.  A plane extends through this trough and objects in that plane are recorded with diagnostic sharpness  Images located at various distances from the plane become less sharp as they get farther from the plane.  Size and shape of the focal trough  Is three dimensional and its actual shape varies depending on the equipment being used.  The main factor that determines the width of the focal trough is the distance from the functional center of the rotation to what is being radiographed.  A general rule the width of the focal trough increases whenever the distance from the rotational center to the object is increased.  Variations in the shape of focal trough  Double—centered rotation  Wide both anteriorly and posteriorly  The distal ends of trough curve mesially  Inward curving is unfavorable to obtaining the best sharpness in the TMJ area  Triple—centered rotation  Show wide posterior and narrow anterior  Requires that the anterior be positioned accurately.  Moving—centered rotation  Show wide posterior and narrow anterior  Requires that the anterior be positioned accurately  Good for facilitating TMJ studies Geometry and Sharpness of the Panoramic Image  Distortion or geometric shape is defined as unequal vertical and horizontal magnification.  Controlled by two different factors:  Vertical direction the focal spot is the actual focal spot in the anode of the tube head.  Horizontal direction the focal spot is the center of rotation.

Errors in Panoramic Radiography Positioning errors

  • Patient is too far forward, too close to film—anterior teeth are blurred and diminished in width
  • Patient is too far back towards the tube head—anterior teeth are blurred and magnified
  • Patient's head is rotated—teeth on the side closer to the film are diminished while the other side is enlarged Positioning of the Spine If the patient’s spine is not straight, the cervical spine will appear as a radiopaque artifact in the center of the film and obscure diagnostic information. Patient’s chin is tipped too low—maxillary teeth are positioned within the focal trough and the mandibular teeth are blurred and magnified. Patient’s chin is raised too high—mandibular teeth are positioned within the focal trough, the maxillary teeth appear blurred and magnified Other Positioning Errors ► Failure to position the chin on the chin rest ► Failure to remove earrings or prostheses ► Failure to keep lips closed ► Failure to keep the tongue on the palate ► Patient movement. ► Failure to use a thyroid collar on the lead apron.