Mandible X-Ray Positioning: AP Axial, PA Axial, and Axiolateral Oblique Views
The mandible is the largest and strongest facial bone, forming the lower jaw and supporting the lower teeth. Although projection radiography remains an important positioning competency, noncontrast maxillofacial CT is usually the initial imaging choice for significant acute mandibular trauma; plain views are used selectively according to the clinical setting and local protocol.
Projection imaging is challenging because the mandible curves through several planes and one side can superimpose the other or the cervical spine. Multiple projections may therefore be used to profile the ramus, body, mentum (chin), and condyloid/coronoid processes. The exact ordered series is institution- and indication-specific, not a universal fixed three-view examination.
This guide reviews commonly taught positioning parameters, rotation adjustments, image-evaluation criteria, trauma precautions, and the distinction between ARRT examination content and local clinical protocols.
For foundational anatomy and projection logic, see our Skull X-Ray Positioning Guide and Facial Bones X-Ray Positioning Guide.
Anatomy of the Mandible
Before positioning, let's review the key anatomic landmarks you'll reference:
| Structure | Description | Palpable? | Positioning Significance |
|---|---|---|---|
| Body | Horizontal U-shaped portion | Yes (jawline) | Visible on PA and oblique views |
| Ramus | Vertical ascending portion (left and right) | No (deep) | Profiled with a true-lateral head position in the axiolateral technique |
| Angle (Gonion) | Junction of body and ramus | Yes — key landmark | Centering point for oblique views |
| Mental protuberance | Chin prominence | Yes | Anterior body reference |
| Condylar process | Posterior superior process whose head articulates at the TMJ | No | Demonstrated on AP axial and PA axial projections |
| Coronoid process | Anterior upper projection | No | Visible on oblique and PA axial |
| Mandibular notch | Depression between condylar and coronoid processes | No | Region assessed with the superior ramus |
| Alveolar process | Tooth-bearing ridge | Yes (gums) | Lower dental arch |
Articulations
The mandible articulates with the temporal bone at the temporomandibular joint (TMJ) — a synovial modified hinge joint permitting rotation and translation. Teeth are anchored in the alveolar sockets by gomphoses, fibrous joints with very limited physiologic mobility.
Core Projection Techniques (Protocol Dependent)
The ARRT Radiography Content Specifications say that listed positions and projections may be covered on the examination. For the mandible, that list contains six projections: axiolateral oblique, PA, AP axial (Towne), PA axial, PA modified Waters, and SMV. It does not define one mandatory three-view clinical series. The following commonly taught techniques must be reconciled with the imaging order and department protocol.
1. Axiolateral Oblique Mandible
The key variable in this projection is the degree of head rotation, which profiles different regions of the side closest to the receptor.
Positioning Parameters
| Parameter | Detail |
|---|---|
| Position | Erect or recumbent; true lateral with side of interest closest to IR |
| SID | 40" (102 cm) |
| CR | 25° cephalad relative to the interpupillary line, directed from the elevated side through the mandibular region of interest |
| Technique | Use the validated technique chart for the detector and patient; 75–85 kVp with a grid is a commonly published teaching range, not a universal prescription |
| Grid/AEC | Grid use and manual versus AEC technique are equipment- and protocol-dependent; collimate closely and do not select a fixed grid ratio from this article |
| Breathing | Suspend respiration |
Rotation Guide
| Region of Interest | Rotation Toward IR | What It Shows |
|---|---|---|
| Ramus | True lateral (0°) | Vertical ramus free of opposite-side superimposition |
| Body | 30° | Mandibular body in profile, elongated |
| Mentum (symphysis) | 45° | Anterior chin projected free of superimposition |
| General survey | Approximately 15° | Overview of the hemi-mandible (when specified by protocol) |
Key positioning points:
- For a nontrauma patient who can move safely, slight neck extension helps prevent the gonion from superimposing the cervical spine
- The CR angle (25° cephalad) combined with appropriate rotation separates the side of interest from the opposite hemi-mandible
- When axiolateral obliques are ordered, both sides are commonly obtained for comparison; follow the ordered series
Evaluation criteria:
- Sharp mandibular margins (no motion)
- Correct obliquity — no foreshortening of the targeted region
- Side of interest free from opposite-side superimposition
- Cervical spine does not overlap the gonion
💡 ARRT Exam Tip
For the standard textbook axiolateral-oblique technique: 0° (true lateral) profiles the ramus, 30° profiles the body, and 45° profiles the mentum. A mnemonic is "Ramus at Rest (0°), Body at Thirty, Mentum at Forty-Five." The usual CR is 25° cephalad relative to the IPL. ARRT identifies this projection as testable, but it does not publish or endorse this mnemonic.
2. PA / PA Axial Mandible
The PA projection demonstrates the rami and lateral body. The PA axial version uses cephalic angulation to elongate the condyloid processes and demonstrate the TMJ region. It should not be called a “Caldwell mandible”: Caldwell is a separately named skull/facial-bone projection.
Standard PA
| Parameter | Detail |
|---|---|
| Position | Erect or prone |
| Part | Nose and forehead on IR; OML ⊥ IR; MSP ⊥ IR |
| CR | Perpendicular, exiting at junction of lips |
| SID | 40" (102 cm) |
| Technique | Use the department's validated technique chart; 75–85 kVp is a published teaching range, not a universal setting |
PA Axial Mandible
| Parameter | Detail |
|---|---|
| CR | 20°–25° cephalad, exiting at the acanthion (junction of upper lip and nose) |
| Result | Elongates the condyloid processes and demonstrates the TMJ region |
Key positioning points:
- Head must not be tilted — the MSP must be truly perpendicular to the IR
- Use PA axial when it is part of the ordered/local protocol; significant acute trauma generally proceeds to noncontrast maxillofacial CT
- Remove dentures, facial jewelry, and earrings before exposure
Evaluation criteria:
- Symmetry of mandibular rami lateral to the spine
- No tilt (equal distance from lateral skull margin to rami on both sides)
- PA axial: condyloid processes elongated and TMJ region clearly demonstrated
- Sharp bone detail (no motion)
💡 ARRT Exam Tip
The 20–25° cephalad CR angle elongates the condyloid processes and demonstrates the TMJ region, whereas the perpendicular PA primarily demonstrates the rami and lateral body. The PA axial mandible is not the Waters or Caldwell facial-bone projection; those have different positioning and centering. See the facial bones positioning guide.
3. AP Axial Mandible (Towne Method)
The AP axial (Towne) projection demonstrates the condyloid processes and temporomandibular fossae, projecting the condyloid processes lateral to the cervical spine when positioning is correct.
| Parameter | Detail |
|---|---|
| Position | Erect or supine |
| Part | OML ⊥ IR; MSP ⊥ IR. If using IOML, increase CR angle by 7° |
| CR | 35° caudad to the OML for the condyloid processes or 42° caudad for the TM fossae, centered at the glabella; if the IOML is perpendicular, use 42° or 49°, respectively |
| SID | 40" (102 cm) |
| Technique | Use the department's validated technique chart; 75–85 kVp is a published teaching range, not a universal setting |
Key positioning points:
- The OML must be perpendicular to the IR — this is critical for correct CR angle application
- If the patient cannot flex enough for OML perpendicular and movement is safe, use the IOML and add 7° to the selected CR angle
- Correct angulation projects the condyloid processes symmetrically lateral to the cervical spine
Evaluation criteria:
- Condyloid processes projected symmetrically lateral to the cervical spine
- Minimal superimposition of mastoid portions over condyles
- Sharp condylar margins (no motion)
- Symmetry between left and right TMJ fossae
🚨 Trauma Safety
Do not flex, extend, or rotate the head and do not remove a cervical collar until the cervical spine has been cleared by the responsible clinical team. If standard positioning is unsafe, maintain immobilization and use the department's trauma modification or proceed to CT as ordered. Do not ask a patient with suspected unstable facial injury to force the mouth open.
Supplemental Projections
SMV (Submentovertex) Mandible
Provides a "bird's-eye" view of the entire mandible, including both condyloid and coronoid processes in a single exposure.
| Parameter | Detail |
|---|---|
| Position | Erect preferred (or supine with hyperextension) |
| Part | Hyperextend neck until IOML ∥ IR; MSP ⊥ IR |
| CR | Perpendicular to IOML, centered midway between mandibular angles |
| Technique | Use the validated local technique chart; exposure and grid use are detector-, patient-, and protocol-dependent |
Demonstrates: A basal two-dimensional view of the mandibular body with the rami and condyloid/coronoid processes. It does not provide three-dimensional fracture assessment. Do not hyperextend a patient whose cervical spine is not cleared; use CT when cross-sectional characterization is required.
Orthopantomography (Panorex)
Panoramic radiography can be useful for selected dental disease or an isolated, uncomplicated mandibular injury in a cooperative patient. It is not the preferred initial study for significant acute mandibular or multi-region facial trauma; the ACR rates noncontrast maxillofacial CT as usually appropriate in that setting.
| Parameter | Detail |
|---|---|
| Patient position | Follow the unit manufacturer's positioning lights/bite-block and local protocol; typically center the MSP without rotation and align the unit's horizontal reference plane |
| Instructions | When the unit requires it, bite in the positioning groove, close the lips, place the tongue against the palate, and remain still |
| Feasibility | Requires cooperation and positioning in the focal trough; may be unsuitable for an immobilized, unstable, or severely injured patient |
| Dose | Varies by unit, field, patient size, and comparison examination; do not promise that it is always lower than a projection series |
Potential advantages in selected patients:
- A single acquisition gives a broad overview of the mandible and dentition
- May reduce the number of separate projections and repositioning steps in a cooperative patient
- Can depict a fracture not visible on one conventional projection
Limitations:
- Inherent magnification, geometric distortion, superimposition, and focal-trough positioning artifacts
- A two-dimensional image does not provide cross-sectional localization or reliable characterization of complex displacement
- Nondisplaced fractures—particularly in the anterior mandible—can be missed
- Does not replace CT when significant or complex facial trauma is suspected
Positioning Summary Table
| Projection | Patient Position | CR | Centering | Key Angle |
|---|---|---|---|---|
| Axiolateral Oblique (Ramus) | Lateral, 0° rotation | 25° cephalad | Mandibular region of interest | 25° cephalad |
| Axiolateral Oblique (Body) | Lateral, 30° rotation | 25° cephalad | Body of mandible | 25° cephalad |
| Axiolateral Oblique (Mentum) | Lateral, 45° rotation | 25° cephalad | Mentum/symphysis | 25° cephalad |
| PA Mandible | Prone or erect | Perpendicular | Exits at lip junction | 0° |
| PA Axial Mandible | Prone or erect | 20–25° cephalad | Exits at acanthion | 20–25° cephalad |
| AP Axial (Towne) | Supine or erect | 35° (condyloid processes) or 42° (TM fossae) caudad to OML | Glabella | Add 7° if using IOML |
| SMV Mandible | Erect (hyperextended) | Perpendicular | Between mandibular angles | Perpendicular to IOML |
For a complete reference on adjacent anatomy, see our Cervical Spine Positioning Guide and Skull X-Ray Positioning Guide.
Common Positioning Errors
| Error | Cause | Fix |
|---|---|---|
| Targeted region foreshortened (oblique) | Rotation does not match the intended ramus/body/mentum view or CR is misangled | Recheck the requested target, head rotation, IPL, and 25° cephalad CR |
| Opposite side obscures the target | Head rotation/CR relationship is incorrect | Reposition to the specified 0°, 30°, 45°, or protocol survey angle; do not automatically add rotation |
| Gonion overlapped by spine | Insufficient extension in a patient safe to move | For a cleared, nontrauma patient, extend slightly; never move an uncleared cervical spine merely to improve the image |
| Condyloid processes poorly projected (Towne) | Wrong baseline, angulation, centering, or rotation | Verify OML versus IOML, use the corresponding 35°/42° or 42°/49° angle, center at glabella, and remove rotation |
| Asymmetric rami (PA) | Head rotation and/or tilt | Check MSP perpendicular and remove both rotation and lateral tilt |
| Motion blur | Motion or excessive exposure time | Explain breathing instructions, use safe immobilization aids that do not obscure anatomy, and use the validated shortest practical exposure |
Clinical Indications and Modality Choice
Projection or panoramic imaging may be ordered selectively for:
- Suspected isolated mandibular fracture: when radiography is appropriate under the local pathway; fractures can be multiple, so the entire mandible must be assessed
- TMJ symptoms: panoramic radiography may show gross osseous abnormality, but it does not evaluate the articular disc; modality selection depends on the clinical question
- Infection: selected evaluation of osteomyelitis or dental infection, often followed by cross-sectional imaging when extent or complications matter
- Neoplastic process: initial or follow-up assessment as directed, with CT/MRI used for characterization and extent
- Pre-/postoperative assessment: selected overview or alignment questions; implant and complex surgical planning commonly require dedicated dental and/or cross-sectional imaging
CT Escalation for Acute Trauma
For trismus, malocclusion, gingival or mucosal hemorrhage, or loose/fractured/displaced teeth after trauma, the ACR Appropriateness Criteria: Imaging of Facial Trauma Following Primary Survey (Variant 4) rates CT maxillofacial without IV contrast “Usually Appropriate” and mandible radiography only “May Be Appropriate.” Escalate directly for suspected complex, displaced, multiple-region, or high-energy injury, or when radiographs are negative/nondiagnostic despite persistent clinical concern.
Exposure, Pregnancy, and Shielding
- Technique: use the department's validated exposure chart, appropriate collimation, and exposure-index targets. Published kVp ranges are teaching examples, not prescriptions for every detector or patient.
- Grid/AEC: selection depends on patient thickness, detector, equipment, and protocol. A fixed grid ratio or blanket AEC rule is not justified across systems.
- Pregnancy: screen according to local policy, but clinically necessary head or facial imaging should not be withheld solely because a patient is pregnant. The uterus is outside the primary beam when the examination is properly collimated.
- Shielding: the current ACR–SPR Practice Parameter for Imaging Pregnant or Potentially Pregnant Patients states that shielding is no longer recommended. Contact shielding does not reduce internal scatter and can obscure anatomy or interfere with exposure control. Follow current facility policy.
For more on managing trauma patients in the X-ray room, see our Trauma Radiography Principles guide.
ARRT Exam FAQs
Q1: What are the three routine projections for the mandible?
There is no universal three-projection series. A common teaching set uses bilateral axiolateral obliques, PA or PA axial, and AP axial Towne, but local protocols vary. ARRT's content outline lists six mandible projections that may be tested and does not prescribe one clinical series.
Q2: Why are oblique positions used rather than a conventional lateral?
Rotation and cephalic angulation reduce superimposition of the opposite side and profile the requested ramus, body, or mentum on the side closest to the IR. A conventional true lateral superimposes both halves, although the axiolateral technique uses a true-lateral head position specifically to profile the ramus.
Q3: How do you check for correct rotation on a PA mandible?
The mandibular rami should appear symmetrical and equidistant from the cervical spine. Asymmetry can result from rotation and/or tilt, so assess both MSP alignment and equal bilateral distances.
Q4: How does PA axial differ from standard PA?
The 20–25° cephalad CR angle elongates the condyloid processes and demonstrates the TMJ region, whereas the perpendicular PA primarily demonstrates the rami and lateral body. Use the projection specified by the order/local protocol; significant acute trauma generally warrants CT.
Q5: What is the primary advantage of panoramic imaging (Panorex)?
A single acquisition provides a broad overview of the mandible and dentition with fewer separate positioning steps. It also has magnification, distortion, superimposition, focal-trough, and cooperation limitations; dose varies by system. It does not replace CT for significant or complex trauma.
📝 Key Takeaway
Know the projection logic: axiolateral oblique uses 0° for the ramus, 30° for the body, and 45° for the mentum with a usual 25° cephalad CR; PA axial uses 20–25° cephalad; mandible Towne uses 35° caudad to the OML for condyloid processes or 42° for TM fossae (add 7° with IOML). These are educational techniques, not a universal fixed series. Never compromise cervical-spine precautions for positioning, and use noncontrast maxillofacial CT for significant acute trauma as directed by the clinical pathway.