Head
Mandible
Anatomy
Students should be able to identify the following structures on themselves, the patient or radiographic images:
Bony Anatomy
Mandible, Body, Mental protuberance, Mental point, Mental foramina, Symphysis menti, Angle (gonion), Rami, Coronoid process, Condylar process, mandibular fossa of the temporal bone, Mandibular notch, Alveolar process.
Topographical Landmarks & Positioning Lines
- Gonion: Posterior angle of the mandible; palpable landmark used for centering oblique views.
- Mentum (mental point): Most anterior midpoint of the chin; used for symphyseal and body projections.
- Orbitomeatal line (OML): Outer canthus to EAM; baseline for Towne projection.
- Infraorbitomeatal line (IOML): Infraorbital margin to EAM; alternate baseline if neck flexion limited.
- Midsagittal plane (MSP): Divides head into right and left halves; perpendicular for PA and AP Axial projections.
- Interpupillary line (IPL): Perpendicular to IR for axiolateral projections to prevent tilt.
Articulations
- Temporomandibular joint (TMJ): Between mandibular condyle and temporal bone; diarthrodial hinge–gliding joint.
- Gomphoses: Between alveolar sockets and teeth; fibrous, synarthrodial (immovable) joints.
Routine Projections (ARRT Required)
Axiolateral Oblique Mandible
Clinical Indications: Fractures, neoplastic or inflammatory processes (both sides for comparison).
CR Location & Positioning
- SID: 40″
- Patient position: Erect or recumbent; true lateral with side of interest closest to IR
- Adjustments:
- Slight extension of neck (avoid superimposition of gonion over spine)
- Rotate head toward IR to place area of interest parallel to IR
- True lateral → ramus
- 30° rotation → body
- 45° rotation → mentum
- 10°–15° rotation → general survey
- CR: Angle 25° cephalad from IPL (alternatives: tilt + CR angle combination not exceeding 25°; or 25° head tilt with perpendicular CR). Direct through mandibular region of interest.
- Pt. Instructions: Suspend respiration.
- Exposure: Digital 75–80 kV, no AEC.
Evaluation Criteria
- Coverage (what anatomy must be included and how you verify it’s complete): Rami, body, mentum, condylar and coronoid processes of side closest to IR
- Rotation checks (how symmetry or alignment tells you if positioning is correct): Correct obliquity prevents foreshortening; side of interest free from opposite side superimposition
- Motion checks (how sharpness confirms patient cooperation/exposure timing): Sharp mandibular margins
- Technique checks (what contrast, density, soft tissue visibility, and artifacts to look for): Adequate contrast/density to visualize entire mandible
- Clinical aim (when applicable, e.g., reflux, obstruction, displacement, etc.): Identify fractures, displacement, or pathology in specific region
PA or PA Axial Mandible
CR Location & Positioning
- SID: 40″
- Patient position: Erect or prone
- Adjustments: Nose & forehead on IR; OML ⟂ IR; MSP ⟂ IR
- CR:
- PA: Perpendicular, exiting junction of lips
- PA axial: 20°–25° cephalad, exiting acanthion
- Pt. Instructions: Suspend respiration.
- Exposure: Digital 75–85 kV.
Evaluation Criteria
- Coverage: Rami and lateral body (PA); condyloid processes and TMJs (PA axial)
- Rotation checks: Symmetry of rami lateral to spine; no tilt
- Motion checks: Sharp bone detail
- Technique checks: Adequate contrast for mandible/TMJ region
- Clinical aim: Assess rami and condyloid processes
AP Axial Mandible (Towne Method)
CR Location & Positioning
- SID: 40″
- Patient position: Erect or supine
- Adjustments: OML ⟂ IR; if IOML used, increase CR angle by 7°; MSP ⟂ IR
- CR: 35°–42° caudad to OML (40° for TM fossae), centered at glabella
- Pt. Instructions: Suspend respiration.
- Exposure: Digital 75–85 kV.
Evaluation Criteria
- Coverage: Condyloid processes and TM fossae
- Rotation checks: Symmetry of condyloid processes lateral to spine
- Motion checks: Sharp condylar margins
- Technique checks: Adequate contrast/density for TM region
- Clinical aim: Condylar displacement, TM joint evaluation
Supplemental Projections
SMV Mandible
CR Location & Positioning
- SID: 40″
- Patient position: Erect preferred (or supine)
- Adjustments: Hyperextend neck until IOML ∥ IR; MSP ⟂ IR
- CR: Perpendicular to IOML, centered midway between angles of mandible (or 1.5″ inferior to symphysis)
- Pt. Instructions: Suspend respiration.
- Exposure: Digital 75–90 kV.
Evaluation Criteria
- Coverage: Entire mandible, including condyloid and coronoid processes
- Rotation checks: Mandible symmetric; condyles equidistant
- Motion checks: Sharp bone margins
- Technique checks: Adequate penetration of mandibular body through skull base
- Clinical aim: Evaluate entire mandible with single projection
Orthopantomography (Panorex) – Mandible
Clinical Indications: Fractures, infection, pre-transplant evaluation; TMJ study.
Key Points
- Digital panoramic system; IOML parallel to floor; MSP aligned with bite-block center line
- Occlusal plane angled slightly down (10° posterior–anterior decline)
- Instruct patient to close lips and place tongue on roof of mouth
- Advantages:
- Low radiation dose (slit collimation)
- Panoramic view of entire mandible, TMJs, teeth, sinuses
- Convenient, less repositioning, shorter exam
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Hows & Whys of Mandible Radiography
Positioning
- Why should mandible images be obtained in oblique positions rather than true lateral?
Oblique positioning prevents superimposition of the opposite mandibular side, allowing clear visualization of the rami, body, or mentum. - Why do you rotate the head 30° toward the IR for the axiolateral oblique projection of the mandible?
This rotation places the mandibular body parallel to the IR for best demonstration. - Why do you rotate the head 45° toward the IR for the axiolateral oblique?
This best demonstrates the mentum (symphysis and anterior portion of the mandible). - Why do you keep the head in a true lateral for the axiolateral oblique?
This position best demonstrates the ramus without superimposition. - Why is slight neck extension important in mandible imaging?
To prevent the gonion from superimposing the cervical spine. - Why is the PA axial projection sometimes preferred over the PA?
The cephalic CR angle elongates the condyloid processes and shows the TMJ region more clearly. - Why is the Towne (AP axial) projection included in mandible studies?
It demonstrates the condyloid processes and TM fossae, which are not well seen on other views. - What other exam can demonstrate the mandible comprehensively?
Orthopantomography (Panorex) provides a panoramic image of the mandible, TMJs, and teeth with lower dose and greater patient comfort. - What are the basic projections required for the mandible?
Axiolateral oblique, PA or PA axial, and AP axial (Towne method). - What is the advantage of a Panorex over routine mandible series?
One panoramic image shows the entire mandible and TMJs with less distortion, reduced radiation exposure, and higher convenience for the patient.
Technique & Image Evaluation
- How do you know the rotation was correct for the ramus on an axiolateral oblique?
The ramus appears without foreshortening and free of overlap from the opposite side. - How do you know the rotation was correct for the body on an axiolateral oblique?
The body appears in profile, elongated, without overlap. - How do you know the rotation was correct for the mentum on an axiolateral oblique?
The mentum is projected free of superimposition and well elongated. - What indicates proper neck extension on axiolateral oblique mandible?
The cervical spine does not overlap the gonion. - How do you check for rotation on a PA or PA axial mandible?
The mandibular rami should appear symmetrical, equidistant from the cervical spine. - What indicates correct CR angle on a Caldwell-style PA axial mandible?
The condyloid processes are elongated and the TMJ region is clearly demonstrated. - How do you know the Towne (AP axial) was positioned correctly?
The condyloid processes are projected symmetrically lateral to the cervical spine, with minimal superimposition of the mastoid portions. - What exposure factors are typical for digital mandible radiography?
Generally 75–85 kVp with a grid; images should show sharp cortical outlines and trabecular detail without motion.
