chapter 26: extraoral radiography

extraoral radiograph

• radiograph 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 radiographs

• evaluate large areas of the skull or jaws

• evaluate growth and development

• evaluate impacted teeth

• detect diseases, lesions and conditions of jaws

• examine the extent of large lesions

• evaluate trauma

• evaluate the TMJ area

extraoral x-ray machine

standard machine may be used for a variety of projections

• some special head positioning and beam alignment devices can be added

• some pano units an be used for these
  - pano tubehead is used in conjunction with cephalostat

cephalostat

special extension arm for pano unit used for extraoral exposures

extraoral film

most are made with screen film placed in a cassette with intensifying screens

screen film

sensitive to light emitted from intensifying screens

intensifying screens

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 (blue) — conventional
  - rare earth (green) — less radiation

cassette purpose

hold the film in tight contact with intensifying screen and to protect the film for exposure to light
- must be labeled to orient specific radiograph
- front side is typically constructed of plastic, back side is made of metal

grid

device used to reduce 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 patients head and film

grid function during exposure

permits passage of x-ray beam between lead strips

• scatter is absorbed by lead strips and does not reach the surface of the film
  - grid = lead foil (functionally)

infection control procedures must be complete before exposing an extraoral film

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

extraoral equipment preparation

• load the extraoral cassette in the darkroom under safelight conditions

• set the exposure factors according to the manufacturers recommendations

extraoral patient prep

explain radiographic procedure to patient

• place double sided lead apron without thyroid collar

• remove all objects from the head and neck region that may interfere with exposure
  - earrings, necklaces, glasses, partials, hearing aids, barrettes, ponytails, clips

lateral jaw radiography

used to examine posterior region of mandible
- body of mandible projection
- ramus of the mandible projection

body of the mandible projection purpose

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

ramus of the mandible projection purpose

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; most often used in oral surgery and ortho
- lateral cephalometric projection
- posteroanterior projection
- waters projection
- submentovertex projection
- reverse towne projection

lateral cephalometric projection purpose

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

posteroanterior projection purpose

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

waters projection purpose

to evaluate the maxillary sinus area

submentovertex projection purpose

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

reverse towne projection purpose

to identify fractures of the condylar neck and ramus area

TMJ radiography

image includes the joint — temporal bone and mandible, as well as, glenoid fossa and articular eminence of the temporal bone, the condyle of the mandible, and the articular disk between the bones
- transcranial projection
- temporomandibular joint tomography

transcranial projection (lindblom technique) purpose

evaluate the superior surface of the condyle and the articular eminence

temporomandibular joint tomography purpose

used to examine the TMJ

• show structures in one area while blurring structures in another area (def of tomography)

• location of rotational point determines what plane of the TMJ will be imaged

• special x-ray equipment is required for tomography

because of limitations existing with interpretation of traditional two-dimensional radiographs,

imaging manufacturers have developed 3D imaging devices specifically for dental purposes using cone-beam technology

cone-beam technology

refers to the use of a cone-shaped x-ray beam to acquire an image
- during scanning a series of projections are acquired

benefits of cone beam technology

• lower radiation dose than traditional

• quick scanning time

• high degree of patient cooperation

• production of anatomically true images

• optimized computer to scan the tissues of oral and maxillofacial complex