Procedures · Head, spine and pelvis3 min read5-question check
Mandible, TMJ, Nasal Bones and Orbits
Rotate the head to choose the part of the mandible, take TMJs open and closed, and use a Caldwell or modified Waters for the orbits.
Mandible
The axiolateral oblique mandible starts with the head lateral, the neck extended so the mandible clears the cervical spine, and the CR angled 25 degrees cephalad. Head rotation picks the part shown. A true lateral shows the ramus. Rotating the head 30 degrees toward the IR shows the body. Rotating 45 degrees shows the mentum, and 10 to 15 degrees gives a general survey. The PA mandible, with the OML perpendicular, shows the rami and body. The PA axial adds a 20 to 25 degree cephalad angle to show the condyles. The AP axial, or Towne, uses 35 degrees caudad to the OML, or 42 degrees to the IOML, to show the condyloid processes and TMJ fossae.
TMJ
The temporomandibular joints are always imaged with the mouth closed and open, because the exam shows motion as well as structure. On the open-mouth image, a normal condyle glides forward to the articular tubercle, also called the eminence. The modified Law method is an axiolateral oblique: start lateral, rotate the face 15 degrees toward the IR, and angle 15 degrees caudad, centering to the TMJ closest to the IR. Both sides are done for comparison. The modified Towne for TMJs uses the AP axial angle above, again open and closed.
Nasal bones
Nasal bones are imaged with laterals of both sides plus a superoinferior tangential, or axial, projection, often with a Waters. For the lateral, center the CR 1/2 inch distal to the nasion. Use a small focal spot and a detail technique with low mAs and kVp, because the bones are small and thin and almost all soft tissue. A lateral with too much technique can burn out a nondisplaced fracture.
Orbits
The Waters, with the OML at 37 degrees to the IR, shows the orbital rims and floors. The modified Waters reduces head extension so the OML forms 55 degrees with the IR and the LML is perpendicular, projecting the petrous ridges into the lower half of the maxillary sinuses. It is a good view of the orbital floors for blowout fractures. For the orbits, the PA axial Caldwell uses 30 degrees caudad, projecting the petrous ridges below the orbits so the orbital floors are clear. The standard 15 degree caudad Caldwell, used for facial bones and sinuses, places them in the lower third of the orbits. The lateral completes the series. Orbit views are also used to screen for metal foreign bodies before MRI.
Clinical Example
A patient who was punched in the left eye has double vision and numbness below the eye. A blowout fracture of the orbital floor is suspected. The radiographer performs a modified Waters, Caldwell, and lateral, and the modified Waters shows soft tissue hanging into the top of the left maxillary sinus.
Common Mistakes
- Doing only a closed-mouth TMJ view; motion needs open and closed images.
- Leaving the neck flexed on a mandible oblique, so the spine overlaps the ramus.
- Using a standard facial bone technique for nasal bones and burning them out.
- Mixing up the 37 degree Waters with the 55 degree modified Waters, or the 15 degree Caldwell with the 30 degree orbits Caldwell.
Why It Matters
The 2027 projection list names the mandible, TMJ, nasal bone, and orbit views directly. These angles and rotations are classic registry facts, and they are easy to confuse without one clear reference.
Key Relationships
- Mandible oblique: 25 degrees cephalad; 0 ramus, 30 body, 45 mentum
- Towne mandible or TMJ: 35 degrees caudad to OML
- Modified Law: 15 degree rotation, 15 degrees caudad
- Nasal bones: CR 1/2 inch distal to nasion, detail technique
- Modified Waters: OML 55 degrees; orbits Caldwell: 30 degrees caudad