Mandible X-Ray Positioning: AP Axial, PA Axial, and Axiolateral Oblique Views
The mandible is the largest and strongest bone of the face, forming the lower jaw and housing the lower teeth. Mandible X-rays are among the most common facial trauma exams performed in the emergency department, and they're a staple of the ARRT radiography exam.
Mandible imaging presents a unique challenge: the bone is curved, thick, and partially superimposed over the cervical spine. That's why no single view tells the whole story. A complete mandible series uses oblique, PA/PA axial, and AP axial projections to visualize each region — the ramus, body, mentum (chin), and the condyloid/coronoid processes — without overlap.
In this guide, you'll learn the exact positioning parameters for each of the three routine projections, the rotation adjustments that target different anatomic regions, common positioning errors, and ARRT exam–tested facts.
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) | Shown in true lateral axiolateral; requires rotation |
| 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 | Upper articular portion (TMJ) | No | Shown on AP axial (Towne) |
| Coronoid process | Anterior upper projection | No | Visible on oblique and PA axial |
| Mandibular notch | Depression between condyle and coronoid | No | Bony landmark for CR centering |
| Alveolar process | Tooth-bearing ridge | Yes (gums) | Lower dental arch |
Articulations
The mandible articulates with the temporal bone at the temporomandibular joint (TMJ) — a diarthrodial hinge-gliding joint that allows opening, closing, and lateral grinding. The teeth articulate with the alveolar sockets via gomphoses — fibrous, immovable joints.
Routine Projections (ARRT Required)
The ARRT radiography content specifications require competency in three projections for the mandible series. According to Clark's Pocket Handbook for Radiographers and Bontrager's Textbook of Radiographic Positioning, these are:
1. Axiolateral Oblique Mandible
This is the most frequently used projection for mandible imaging. The key variable is the degree of head rotation, which targets different regions of the mandible.
Positioning Parameters
| Parameter | Detail |
|---|---|
| Position | Erect or recumbent; true lateral with side of interest closest to IR |
| SID | 40" (102 cm) |
| CR | 25° cephalad from interpupillary line; direct through mandibular region of interest |
| kVp | 75–80 (digital) |
| Grid | Yes (8:1 or 10:1) |
| Breathing | Suspend respiration |
| AEC | Not recommended |
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 | 10°–15° | Overview of entire hemi-mandible |
Key positioning points:
- Extend the neck slightly — this prevents 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
- Always obtain both sides for comparison in trauma cases
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
The rotation degrees for the axiolateral oblique are frequently tested: 0° (true lateral) = ramus, 30° = body, 45° = mentum. A mnemonic to remember: "Ramus at Rest (0°), Body at Thirty, Mentum at Forty-Five." The CR is always 25° cephalad regardless of rotation. This is a classic registry question — know the rotation values cold.
2. PA / PA Axial Mandible
The PA projection provides a straight-on view of the mandibular body and rami. The PA axial (Caldwell-style) version with cephalic angulation elongates the condyloid processes for better TMJ assessment.
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) |
| kVp | 75–85 (digital) |
PA Axial (Caldwell Method for Mandible)
| Parameter | Detail |
|---|---|
| CR | 20°–25° cephalad, exiting at the acanthion (junction of upper lip and nose) |
| Result | Elongates condyloid processes; better demonstrates TMJ region |
Key positioning points:
- Head must not be tilted — the MSP must be truly perpendicular to the IR
- The PA axial with cephalic angulation is preferred when condylar pathology is suspected
- 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
Why is the PA axial sometimes preferred over the standard PA? The 20–25° cephalad CR angle elongates the condyloid processes and shows the TMJ region more clearly. This is a commonly tested distinction: PA = condyles foreshortened, PA axial = condyles elongated. Also note: the PA axial is not the same as the Waters or Caldwell views for facial bones — those are different projections with their own centering. For more on those, see our facial bones positioning guide.
3. AP Axial Mandible (Towne Method)
The Towne method (also called the AP axial or fronto-occipital projection) is essential for visualizing the condyloid processes and mandibular fossae of the temporal bone — areas that are obscured on the PA projections.
| Parameter | Detail |
|---|---|
| Position | Erect or supine |
| Part | OML ⊥ IR; MSP ⊥ IR. If using IOML, increase CR angle by 7° |
| CR | 30°–37° caudad to OML (or 35°–42° per other standard references), centered at the glabella |
| SID | 40" (102 cm) |
| kVp | 75–85 (digital) |
Key positioning points:
- The OML must be perpendicular to the IR — this is critical for correct CR angle application
- If the patient cannot flex the neck enough for OML perpendicular, use the IOML baseline and increase CR angle by approximately 7°
- The CR should pass through the foramen magnum to project the condyles lateral to the spine
- A mouth-open Towne brings the condyles forward out of the mandibular fossae, giving better visualization of condylar fractures
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
🚨 Clinical Pearl
A mouth-open Towne brings the condyles forward out of the TM fossae, which is especially useful for trauma patients with suspected condylar fractures — a common injury in falls and facial trauma. However, for unconscious or uncooperative patients who cannot hold their mouth open, the closed-mouth Towne still provides diagnostic information about condylar position and displacement.
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 |
| kVp | 75–90 (digital) |
Best for: Evaluating the entire mandibular contour, especially in complex trauma where the relationship between fracture fragments must be assessed in three dimensions.
Orthopantomography (Panorex)
Panoramic radiography is often the first-line imaging study for mandible trauma and dental pathology.
| Parameter | Detail |
|---|---|
| Patient position | Erect with IOML parallel to floor, MSP aligned with bite-block center |
| Occlusal plane | ~10° posterior-anterior decline |
| Instructions | Close lips, place tongue on roof of mouth, remain still |
| Dose | Lower than a full mandible series (slit collimation) |
Advantages over routine series:
- Single panoramic image shows entire mandible, TMJs, and teeth
- Less distortion than manual series
- Lower radiation dose (slit-beam collimation)
- Faster exam with less patient repositioning
- Better tolerated by trauma patients
Limitations:
- Less spatial resolution than intraoral or direct radiography
- Does not replace orthogonal views for fracture characterization
- May miss non-displaced fractures of the anterior mandible
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 | 30–42° caudad | Glabella | 30–42° caudad (OML) |
| 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 |
|---|---|---|
| Ramus foreshortened | Insufficient rotation or incorrect CR angle | Ensure true lateral for ramus; verify 25° cephalad CR |
| Opposite side superimposing | Insufficient rotation | Increase rotation toward IR per the rotation guide |
| Gonion overlapped by spine | Neck not extended | Slightly extend neck to elevate the mandible away from C-spine |
| Condyles not visible (Towne) | CR angle too shallow | Increase to 35–42° caudad; verify OML ⊥ IR |
| Asymmetric rami (PA) | Head tilt | Check MSP ⊥ IR; ensure no lateral tilt |
| Motion blur | Insufficient immobilization | Use head clamps or sandbags; short exposure time |
| Petrous ridges over maxillae (PA) | Neck too extended | Flex neck so OML is truly perpendicular |
Clinical Indications for Mandible Imaging
Common reasons a mandible X-ray is ordered:
- Trauma: Falls, assault, motor vehicle accidents, sports injuries
- Mandibular fracture: Most common facial fracture after nasal bone; ~50% involve the body
- TMJ dysfunction: Pain, clicking, limited opening
- Infection: Osteomyelitis, dental abscess extension
- Neoplastic process: Primary or metastatic lesions
- Pre-surgical planning: Orthognathic surgery, dental implant assessment
- Post-reduction evaluation: Check alignment after fracture fixation
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?
The basic mandible series includes: (1) axiolateral oblique (with appropriate rotation for ramus, body, or mentum), (2) PA or PA axial, and (3) AP axial (Towne method). Each projection has a specific purpose and demonstrates different anatomic regions.
Q2: Why must mandible images be obtained in oblique positions rather than a true lateral?
Oblique positioning prevents superimposition of the opposite mandibular side, allowing clear visualization of the rami, body, or mentum of the side closest to the IR. A true lateral would superimpose both halves of the mandible, making interpretation impossible.
Q3: How do you check for correct rotation on a PA mandible?
The mandibular rami should appear symmetrical and equidistant from the cervical spine. Any asymmetry indicates head tilt or incorrect rotation. The distance from the lateral skull margin to the ramus should also be equal on both sides.
Q4: Why is the PA axial projection sometimes preferred over the standard PA?
The 20–25° cephalad CR angle elongates the condyloid processes and demonstrates the TMJ region more clearly than the perpendicular PA projection. Use PA axial when condylar or TMJ pathology is part of the clinical question.
Q5: What is the primary advantage of panoramic imaging (Panorex) over a routine mandible series?
A single panoramic image shows the entire mandible, TMJs, and teeth with less distortion, lower radiation dose, and greater patient convenience. However, it does not provide the orthogonal two-plane evaluation needed for definitive fracture characterization.
📝 Key Takeaway
Master the three-view mandible series: axiolateral oblique (with rotation guide: 0° ramus, 30° body, 45° mentum), PA/PA axial, and AP axial Towne. The axiolateral oblique is the workhorse view, the PA axial shows condyles best, and the Towne is essential for condylar fractures. On the ARRT, expect questions on rotation degrees, CR angles, and the rationale behind oblique positioning. Also know the Towne CR angle range (30–42° caudad) and why the PA axial elongates the condyles. For adjacent head and neck positioning, review our cervical spine and facial bones guides.