Zygomatic Arches, Mandible and TM Joints Flashcards
SMV zygomatic arches
- MSP perp to IR
- IOML parallel to IR
- CP: 1” posterior to outer canthus of the eye
- SID 100
- CR: perpendicular to IOML - exiting through the arches
- strip collimate
- bilateral arches
SMV zygomatic arches evaluation criteria
- zygomatic arches free from overlying structures
- symmetric and without foreshortening
- no rotation or tilt of head
Oblique Axial Tangential projection - Zygomatic arches
- IOML parallel to IR
- CR perp to IOML
- rotate MSP 15 toward side being examined
- tilt chin 15 toward the side being examined
- CP - through zygomatic arch - 1” posterior to outer canthus of the eye
AP Axial - Modified Towne - Zygomatic Arch
- OML perp to IR
- CR - 30 caudad
- CR passes through the middle of the arches
- strip collimation
AP Axial - Modified Towne - Zygomatic Arch - evaluation criteria
no rotation
- symmetric projection of both zygomatic arches
- no overlap by mandible
zygomatic arches are projected lateral to mandibular rami
what is countercoup?
mandible fractured in 2 places
Lateral mandible
- IOML perp to front edge of IR
- IPL perp to IR
- CR perp
- CP - center of mandible
- affected side closest to IR
Axiolateral oblique mandible
- project one side above the other - imaging side closest to the IR
- CR - 25 cephalad
- IP perp to IR
- erect (semi prone), or semi-supine on table
Axiolateral mandible for the ramus
keep head in true lateral
Axiolateral mandible for the body
rotate nose 30 toward IR or until body of mandible is parallel to IR
Axiolateral mandible for the symphysis
rotate nose 45 toward IR
Axiolateral mandible for general survey
rotate nose 15-20 toward IR
Erect Axiolateral oblique for the Ramus
- head in a true lateral
- chin elevated
- CR 25 cephalad OR tilt vertex 15 towards IR and angle CR 10 cephalad
- CP enter between symphysis menti and EAM - inferior and anterior to remote gonion
- must include TMJ on dependent side - do not need TMJ on remote side
- shadow of the shoulder must be below the mandible
why is a 25 degree tilt not recommended?
when tilt is used the ramus becomes foreshortened
Erect axiolateral oblique for the body
- nose rotated 30 towards IR - body of the mandible parallel with IR
- CR - 25 cephalad
- CP - just inferior to gonion - light will go posterior to remote EAM
Semi supine axiolateral mandible
- place 45 sponge behind patient
- head true lateral on detector
- CR 25 cephalad - provided IP line is perpendicular to the IR
- Demos dependent side
- non grid technique
AP/PA mandible
- forehead and nose on Bucky
- OML perp to IR
- make sure light above EAM and below symphysis menti
- suspend respiration
AP Axial - Modified Towne - Mandible
- OML perp IR
- CR - 35 caudad
- CP - midway between EAM and Symphysis Menti
Angle for modified Towne mandible
- For any Modified Towne involving the Mandible requires More angle. This includes the TM joints.
- The Modified Towne for zygomatic arches…30° caudad because the arches are not part of the mandible
AP Axial - modified towne - mandible - evaluation criteria
- include symphysis menti
- good visualization of the condyles
- increased angle equals increased elongation
- assess medial or lateral displacement
PA Axial Mandible
- OML perp to IR
- CR - 20-25 cephalad
- CP - exits near acanthion - center between EAM and symphysis menti
- suspend respiration
why is less angle used for PA Axial mandible versus AP Axial mandible?
Less angle compared to the AP axial because too much of the spine is projected over the mandible with the larger angle
PA Axial mandible - evaluation criteria
- demonstrates body and ramus
- good for medial or lateral displacement of fractures
- not good for visualization of symphysis menti
- condyles demonstrated
what is panoramic tomography?
digital xray beam that is sharply collimated at a fixed SID
- rotation takes 10-20 seconds
