ch 26: Extraoral Radiography

extraoral radiograph

-A radiograph that is placed outside the mouth during x-ray exposure

-Used to image large areas of the skull or jaws

-Often used in orthodontics and oral surgery

purpose and use of extraoral radiograph

-To evaluate large areas of the skull or jaws

-To evaluate growth and development

-To evaluate impacted teeth

-To detect diseases, lesions, and conditions of the jaws

-To examine the extent of large lesions

-To evaluate trauma

-To evaluate the temporomandibular joint area

x-ray unit

-A standard intraoral x-ray machine may be used for a variety of extraoral projections

-Special head positioning and beam alignment devices can be added

-Some panoramic x-ray units can be used for extraoral projections

-The panoramic tubehead is used in conjunction with a special extension arm and a device known as a cephalostat

film

Most extraoral exposures are made with screen film placed in a cassette with intensifying screens

screen film

sensitive to the light emitted from intensifying screens

intensifying screen

-A device that converts x-ray energy into light; the light, in turn, exposes the film

-the film must be compatible with the light emitted from the screen

-Specific film must be used with certain screens

Calcium tungstate (conventional)

blue

Rare earth

green; uses less radiation

cassette

-Purpose is to hold the film in tight contact with the intensifying screen and to protect the film from exposure to light

-Must be labelled to orient the finished radiograph (R & L)

-The front side is typically constructed of plastic, back side is made of metal

grid

-A device used to reduce the amount of scatter radiation that reached an extraoral film during exposure

-A series of thin lead strips embedded in a material that permits passage of the x-ray beam

-placed between the patient’s head and the film

-During exposure, the grid permits passage of the x-ray beam between the lead strips

-Scatter radiation is absorbed by the lead strips and does not reach the surface of the film

-made of lead foil

step-by-step procedures

-Infection control procedures must be complete before exposing an extraoral film

-If an extraoral unit with cephalostat is used, the ear rods must be wiped with disinfectant between patients

equipment preparation

-Load the extraoral cassette in the darkroom under safelight conditions

-Set the exposure factors according to the manufacturer’s recommendations

patient preparation

-Explain the radiographic procedure to the patient

-Place a double sided lead apron (if applicable) without a thyroid collar over the patient and secure it

-Remove all objects from the head and neck region that may interfere with film exposure (Earrings, necklaces, glasses, partials, hearing aids, barrettes, ponytail ties)

patient positioning

Varies with each extraoral radiographic projection

lateral jaw radiography

Used to examine the posterior region of the mandible

types of lateral jaw radiography

-Body of the mandible projection

-Ramus of the mandible projection

purpose of the body of the mandible projection

To evaluate impacted teeth, fractures, and lesions located in the body of the mandible

purpose of the ramus of the mandible projection

To evaluate impacted third molars, large lesions, and fractures that extend into the ramus of the mandible

skull radiography

-Used to examine the bones of the face and skull

-Used most often in oral surgery and orthodontics

types of skull radiography

-Lateral cephalometric projection

-Posteroanterior projection

-Waters projection

-Submentovertex projection

-Reverse Towne projection

purpose of lateral cephalometric projection

To evaluate facial growth and development, trauma, and disease and developmental

purpose of posteroanterior projection

To evaluate facial growth and development, trauma, and disease and developmental abnormalities

purpose of waters projection

To evaluate the maxillary sinus area

purpose of submentovertex projection

To identify the position of the condyles, demonstrate the base of the skull, and evaluate fractures of the zygomatic arch

purpose of the reverse towne projection

To identify fractures of the condylar neck and ramus area

TMJ radiography

The joint includes the temporal bone and the mandible

-The glenoid fossa and articular eminence of the temporal bone, the condyle of the mandible, and the articular disk between the bones comprise the TMJ

types of TMJ radiography

-Transcranial projection

-Temporomandibular joint tomography

purpose of transcranial projection (Lindblom Technique)

To evaluate the superior surface of the condyle and the articular eminence

purpose of TMJ tomography

-to examine the temporomandibular joint

-The location of the rotational point determines what plane of the TM joint will be imaged

tomography

Show structures in one area while blurring structures in another area

cone-beam technology

-Imaging manufacturers have developed three- dimensional imaging devices specifically for dental purposes

-refers to the use of a cone-shaped x-ray beam to acquire an image

-During scanning, a series of projections are acquired; this digital information provides data for reconstruction of the image using a computer

benefits of cone-beam technology

-A lower radiation dose for the patient than with traditional CT

-A quick scanning time

-A high degree of patient cooperation

-Production of anatomically true images

-Optimized computer to scan the tissues of the oral and maxillofacial complex