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TMJ X-Ray Positioning: Open and Closed Mouth Views for Radiologic Technologists

The temporomandibular joint (TMJ) is a paired synovial, ginglymoarthrodial (hinge-and-glide) joint between the mandibular condyle and the temporal bone. Early opening is predominantly rotation; translation becomes more prominent as the condyle-disc complex moves anteriorly along the articular eminence.

This guide separates commonly confused named methods and places conventional radiography in its modern clinical context. Plain films show osseous contours and gross condylar excursion, but they do not directly show the articular disc, capsule, effusion or muscles and should not be used to diagnose internal derangement.

Anatomy and What a Plain Film Can Show

Structure	Accurate imaging statement
Mandibular condyle and neck	Visible on appropriately positioned projections; assess contour, alignment and gross displacement.
Mandibular fossa and articular eminence	Temporal-bone landmarks visible to varying degrees, with projectional distortion and superimposition.
Articular disc	Dense fibrous connective tissue; not visible on plain radiography. MRI is the preferred examination for disc position and morphology.
Joint “space”	A projectional radiolucency, not a direct image of disc thickness. Head position and beam geometry alter its appearance.
External acoustic meatus (EAM)	A positioning landmark. Entry points differ by named projection and refer to the upside EAM when the ray exits the downside joint.

Indications and Modality Selection

Imaging is chosen after clinical assessment when the result is expected to affect management. Examples include trauma or dislocation, suspected osseous degenerative/inflammatory disease, developmental abnormality, neoplasm, and suspected internal derangement. Pain, clicking or limited opening alone does not make a particular X-ray series automatically appropriate.

Clinical question	Typical imaging role
Initial broad osseous survey	Panoramic radiography may be used, recognizing limited sensitivity and superimposition.
Fracture/acute complex trauma	CT is generally preferred; CBCT can provide excellent osseous detail when soft-tissue assessment is not required and local capability is appropriate.
Degenerative osseous change, ankylosis, developmental anomaly	CBCT or CT provides multiplanar bony assessment superior to conventional radiography.
Disc displacement, effusion or other internal derangement	MRI, usually with closed- and open-mouth sequences, is preferred.
Inflammatory arthritis	Modality depends on the question: MRI for active synovitis/effusion and marrow/soft tissue; CBCT/CT for osseous change.

How Many Images Are in a TMJ Series?

There is no universal fixed count. A common conventional series comprises right and left axiolateral or axiolateral-oblique views, each closed and open (four images). A department that also requires an AP axial modified Towne closed/open pair will obtain six. Some orders require fewer images or another modality. Follow the written order and departmental protocol rather than adding exposures to satisfy a memorized number.

1. Axiolateral TMJ — Schüller Method

In commonly taught U.S. radiographic positioning, Schüller is a true-lateral, transcranial axiolateral method. It is not synonymous with modified Law.

Parameter	Commonly taught Schüller protocol
Position	Erect or recumbent true lateral; side of interest (downside TMJ) against the receptor; MSP parallel and IPL perpendicular to the receptor.
Central ray	25–30° caudad, directed from the upside to the downside TMJ.
Entry/exit	A common textbook entry is about 1.3 cm (½ in) anterior and 5 cm (2 in) superior to the upside EAM, exiting the downside TMJ. Confirm the exact landmark specified by the department's adopted procedure guide.
Mouth	Closed and open exposures when ordered and safe. Do not force opening.
Demonstrates	The TMJ nearest the receptor, projected inferior to the opposite side; osseous relationship and gross change in condylar position.

Evaluation: include the downside condyle, fossa and articular eminence; avoid rotation/tilt between paired images; show sharp cortical margins and adequate separation from the opposite joint. Do not require a supposedly “uniform 2–3 mm” joint space or infer disc integrity from this projection.

2. Axiolateral Oblique TMJ — Modified Law Method

Modified Law combines head rotation with a smaller tube angle. Mixing its 15° angle with the Schüller name was the central technical error in the previous version of this page.

Parameter	Commonly taught modified Law protocol
Position	Side of interest nearest the receptor; from lateral rotate the face/MSP 15° toward the receptor; keep IPL perpendicular.
Central ray	15° caudad, centered to exit the downside TMJ.
Entry	Common procedure guides describe entry about 3.8 cm (1½ in) superior to the upside EAM; centering language varies, so follow the adopted protocol.
Mouth	Closed and open exposures when ordered and tolerated.
Demonstrates	Downside TMJ with the opposite joint displaced by the combined rotation and caudad angulation.

3. AP Axial TMJ — Modified Towne Method

This bilateral projection demonstrates the condylar processes in an AP axial orientation. It does not project the condyles “through the foramen magnum”; that description confuses this view with a different skull evaluation criterion.

Parameter	Commonly taught modified Towne protocol
Position	Supine or erect with posterior skull at receptor; MSP perpendicular; OML perpendicular if safely achievable.
Central ray	35° caudad to the OML, entering approximately 7.5 cm (3 in) superior to the nasion. If IOML is perpendicular, use 42° caudad to the IOML.
Mouth	Closed and open exposures may be specified. Do not open the mouth if contraindicated by trauma, pain or instability.
Demonstrates	Bilateral condylar processes and gross side-to-side symmetry/relationship.

Evaluation: condylar processes should be symmetric, with no head rotation; petrous portions should be symmetric; open and closed images should have reproducible head position. A modified Towne image does not establish disc status.

Incorrect and Historical Projection Names

Term	Accuracy note
“PA transoral TMJ”	Not a standard bilateral TMJ projection. A perpendicular beam through the open mouth does not create the claimed unobstructed view of both TMJs. It has been removed from this guide.
Transpharyngeal (Parma and variants)	Historical lateral-oblique dental view through the pharynx, primarily depicting the condyle/neck with distortion and superimposition. Parma's contact technique is specifically discouraged in the reviewed literature.
Transorbital (Zimmer and variants)	Historical frontal approach through the ipsilateral orbit toward the TMJ. It places the lens in or near the primary beam and is not recommended for routine TMJ evaluation.
Transcranial	A category that includes lateral approaches such as Schüller/modified Law; it provides only a projectional view of part of the osseous joint.

Do not improvise angles for historical dental views. If one is specifically requested, obtain the facility's validated protocol and confirm the order with the radiologist or appropriately authorized practitioner.

Positioning Summary

Projection	Head	Central ray	Side shown
Schüller axiolateral	True lateral	25–30° caudad	Downside/nearest receptor
Modified Law axiolateral oblique	15° toward receptor	15° caudad, exits downside TMJ	Downside/nearest receptor
Modified Towne AP axial	OML perpendicular (or IOML alternative)	35° caudad to OML (42° to IOML), entering ~7.5 cm above nasion	Both condylar processes

Technique, Dose and Patient Safety

• Technique: use the current equipment-specific technique chart, appropriate SID/receptor/grid policy, tight pre-exposure collimation and the shortest practical exposure time. A universal kVp or grid ratio is not evidence-based across all detector systems.
• Dose: do not quote one “TMJ series dose” without the device, projection count and dose metric. Avoid repeats by confirming side, mouth position, baseline and tube angle before exposure.
• Pregnancy: a medically indicated head examination should not be withheld solely because of pregnancy. Verify pregnancy according to policy, explain that the uterus is outside the primary beam, optimize/collimate, and consult the radiologist or medical physicist for case-specific concerns.
• Shielding: AAPM recommends discontinuing routine patient gonadal/fetal shielding because benefit is negligible and shields can obscure anatomy or interfere with exposure systems. Follow current law and facility policy; never place shielding in the primary beam.
• Scope: radiographers acquire images at the request of and for interpretation by a licensed practitioner. They assess image quality and document observations/procedure details under policy, but do not independently diagnose disc displacement, fracture or dislocation.

Trauma and Cervical-Spine Safeguards

Do not attempt reduction. After a clinician reduces a dislocation, perform only the ordered post-reduction imaging and remain alert to pain, airway difficulty and recurrent dislocation.

Common Errors and Corrections

Problem	Likely issue	Response
Opposite TMJ overlaps the downside joint	Wrong named-method geometry, head rotation/tilt, or centering error	Confirm whether Schüller or modified Law was ordered; restore that method's complete geometry rather than arbitrarily increasing angle.
Open/closed pair cannot be compared	Head moved between exposures	Reproduce MSP/IPL and centering; repeat only if the image is nondiagnostic and authorized by policy.
Modified Towne condyles asymmetric	Head rotation or tilt	Correct MSP/IPL if safe; do not manipulate a potentially unstable cervical spine.
Blur	Motion during uncomfortable open-mouth hold	Explain first, prepare completely before opening, support safely, and use a short exposure. Never force or insert an unapproved bite device.
Exposure or anatomy inadequate	Generic technique, large field, wrong landmark	Use the validated technique chart and projection-specific landmark; collimate to required anatomy.

Interpreting Open and Closed Mouth Images

Observation on plain film	What may safely be said	What cannot be concluded
Change in condylar position with opening	Gross osseous excursion can be compared if positioning is reproducible.	Normal disc function cannot be proved.
Limited/asymmetric excursion	Nonspecific finding that may support further clinical/imaging assessment.	Does not diagnose disc displacement, effusion or muscle spasm.
Condyle persistently anterior to eminence in a patient unable to close	May support suspected anterior dislocation; urgent clinical/radiologist assessment is appropriate.	The technologist should not make or communicate an independent final diagnosis.
Flattening, sclerosis, erosion or osteophyte	Possible osseous degenerative change; CBCT/CT characterizes bone better.	Symptoms, inflammatory cause or disc status cannot be determined from the film alone.
Suspected fracture/displacement	Escalate promptly under critical-findings policy.	A negative conventional series does not reliably exclude fracture.

Frequently Asked Questions

How many images are in a conventional TMJ series?

There is no universal count. Bilateral axiolateral or axiolateral-oblique closed/open pairs commonly produce four images. A protocol that also requests a modified Towne closed/open pair produces six. Obtain only the ordered, locally approved images.

Are Schüller and modified Law the same projection?

No. In the teaching conventions used here, Schüller uses a true-lateral head and a 25–30° caudad CR. Modified Law uses 15° rotation toward the receptor and a 15° caudad CR. Both depict the downside joint, but their geometry must not be mixed.

What do closed- and open-mouth radiographs establish?

They compare osseous condylar position and gross excursion when positioning is reproducible. They do not directly depict the disc and cannot by themselves diagnose disc displacement, effusion or muscle spasm.

Is a PA transoral image a standard TMJ projection?

No. It does not provide the previously claimed unobstructed bilateral TMJ image. Historical transpharyngeal and transorbital methods also are not recommended for routine TMJ evaluation by current AAOMR/AAOP guidance.

Which modality is preferred for bone versus the articular disc?

CBCT or CT is selected for detailed osseous assessment, including fracture or degenerative change. MRI is preferred for disc position, effusion and other soft tissues. Modality selection depends on the clinical question and authorized order.

Practice Questions

Authoritative Sources

• AAOMR/AAOP position statement: Recommendations for imaging of the temporomandibular joint
• Peer-reviewed review of TMJ imaging modalities and limitations of classical projections
• AAPM patient gonadal and fetal shielding position statement
• ASRT Practice Standards
• ARRT Examination Content Specifications