Modified Law Method : TMJ

Tuesday, January 13, 2015

X-ray of the Temporomandibular Joint (TMJ)

Axiolateral Projection - Right or Left Positions

Abnormal relationship or rang of motion between condyle and TM fossa is shown. Usually these projection taken in open and closed mouth positions.
Modified Law method is an x-ray special projection to best demonstrate the abnormal relationship of temporo-mandibular fossa or TMJ, which also known as rang of motion between condyles and TM fossa. Commonly this projectjion is taken in open and closed mouth position.
Technical Factors and Patient Position:
tmj oblique
Upright Axiolateral (Right Anterior Oblique)
  • Image receptor size is 18 x 24 or 8 x 10 inches, Lengthwise
  • Moving or Stationary Grids
  • 70 to 80 kV range, mAs is 14 and use small focal spot.
  • Patient is in erect or semiprone position but erect is preferred in this projection/method if patient condition allows. The lateral portion of the head is rested against IR, table or bucky, with the area of interest closest to image receptor
Part Position, Central Ray, Collimation and Respiration:
  • IPL is perpendicular to cassette to prevent tilting.
  • Midsagittal plane is parallel to cassette.
  • IOML is perpendicular to front edge of cassette.
  • Rotate head from lateral position (face down towards bucky or cassette by 15°)
  • midsagittal plane of the head is rotated 15° from flat surface or plane of cassette.
  • Angle central ray 15° caudad centered to 4 cm superior to upside EAM. (to pass through downside TMJ).
  • Image receptor and collimation must be align and centered.
  • SID is 40 inches.
  • Collimate on all side of IR to yield a field size of apprx. 4 inches square.
  • Suspended respiration during exposure to minimize patient motion.
Radiographic Criteria on Modified Law Method:
Structure Shown:
  • The Temporomadibular joint nearest to cassette is visible. Closed mouth position demonstrate condyle within mandibular fossa.
  • In open mouth the condyle moves to the anterior margins of the madibular fossa.
tmj oblique
Open Mouth Axiolateral Projection
Correct Patient Positioning:
  • The TMJ or the area of interest is clearly demonstrated with superimposition of opposite TMJ. (15° rotation of head from lateral prevent this superimposition.)
  • Cervical spine is not superimposed to the Temporomandibular Joint interest.
Correct Collomation and Central Ray:
  • TMJ of interest is in the middle of image.
Correct Exposure or Technic Factor use:
  • Contrast and density are enough to visualize TMJ.
  • Sharp bony margins indicates no motion.

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