A client may report difficulty opening the mouth, jaw stiffness, clicking, discomfort chewing, symptoms with yawning, or a change in jaw movement after a flare-up or period of guarding.
The TMJ Depression Test gives a simple way to quantify jaw opening. It does not explain the cause of reduced opening on its own, but it provides useful baseline information when interpreted alongside pain, symptoms, jaw deviation, TMJ sounds, cervical range of motion, headache history, chewing tolerance and related jaw movement tests.
Test name: TMJ Depression Test
Purpose: Measure jaw opening range of motion
Movement: Opening the mouth by lowering the mandible
Joint/body region: Temporomandibular joint and jaw
Plane: Primarily sagittal plane
ROM type: Active opening, comfortable opening, assisted opening or passive opening
Score: Maximum interincisal opening in millimetres
Equipment: Millimetre ruler, disposable measurement card, calipers or Measurz recording workflow
Best used with: TMJ translation, lateral deviation, jaw closing, cervical ROM, headache assessment, chewing function and symptom tracking
Key limitation: Jaw opening values vary by age, sex, body size, pain, dental status, overbite, measurement method and symptom irritability
The TMJ Depression Test measures the range available when the mouth opens.
In most clinical and field settings, jaw opening is measured as the distance between the edges of the upper and lower central incisors during maximum opening. This is often called maximum interincisal opening.
The test can be performed as:
comfortable opening
active maximum opening
assisted opening
passive opening
Each version should be recorded separately because results may differ.
The test is used to establish a baseline, compare change over time and monitor jaw movement.
It may help inform:
jaw opening capacity
symptom response during mouth opening
chewing and yawning tolerance
mouth opening limitation
TMJ movement monitoring
headache or neck-related assessment context
progress tracking after changes in symptoms or loading
decisions about whether related tests would add context
The test measures jaw opening range, usually in millimetres.
It may be influenced by:
TMJ movement
mandibular control
pain or symptoms
muscle guarding
jaw deviation
dental alignment
overbite or overjet
joint sounds
cervical posture
headache symptoms
measurement method
client effort or apprehension
Reduced TMJ depression provides movement information, but it does not explain the cause on its own.
Active TMJ depression measures how far the client can open the mouth using their own control.
Passive or assisted TMJ depression measures how far the mouth can open when gentle assistance is provided.
Comparing active and assisted opening can help separate available movement from pain inhibition, guarding, confidence or motor control.
Passive or assisted opening should be gentle and should not force symptoms.
This test may be useful for clients with:
jaw stiffness
reduced mouth opening
chewing discomfort
jaw clicking or catching
symptoms during yawning
headache or neck symptoms with jaw involvement
sport-related jaw or facial impact history
difficulty with dental or oral tasks
side-to-side jaw movement differences
It is also useful when comparing jaw movement across sessions.
Disposable millimetre ruler or measurement card
Calipers if available and appropriate
Gloves if required by setting
Mirror if observing deviation
Pain or symptom scale
Measurz for recording ROM, pain, symptoms and progress
Optional notes for TMJ sounds, jaw deviation and cervical symptoms
Position the client sitting upright in a relaxed posture.
Use the same position for every retest.
The client keeps the head steady, shoulders relaxed and eyes facing forward.
Stand or sit in front of the client so the jaw, lips and teeth can be observed.
Ask the client to start with the teeth lightly together or jaw relaxed, depending on the protocol.
Avoid holding the jaw unless performing an assisted version. Keep the head and neck position consistent.
For active ROM, ask the client to open the mouth as wide as comfortably possible.
For comfortable opening, ask the client to open as far as feels comfortable without pushing into symptoms.
For assisted opening, gently assist only if appropriate and within scope.
Measure the vertical distance between the incisal edge of the upper central incisor and the incisal edge of the lower central incisor.
If teeth are missing, use consistent alternative landmarks and record them clearly.
Ask about pain, stiffness, clicking, catching, locking, headache symptoms, ear symptoms, tooth discomfort and whether the movement feels familiar.
Stop if pain increases sharply, the jaw locks, symptoms spread, dizziness occurs, the client becomes apprehensive, or movement is not tolerated.
Record active or assisted method, opening distance in millimetres, pain score, symptom location, joint sounds, deviation, dental landmark used and stopping reason.
One to three trials may be used. Record the best, average or selected trial consistently.
Use the same position, landmarks, measurement tool, opening instruction and endpoint definition each time.
The score is recorded in millimetres.
A higher value generally indicates greater jaw opening under the tested setup. A lower value indicates less mouth opening compared with previous baseline, broad reference values or the client’s functional needs.
Interpretation is stronger when combined with:
pain score
symptom location
comfortable versus maximum opening
active versus assisted opening
jaw deviation
TMJ sounds
chewing tolerance
cervical ROM
headache symptoms
related TMJ movement tests
The result does not explain the cause of reduced movement by itself. It helps guide monitoring, education and further assessment decisions.
Evidence level: Level 3 — broad reference values are available, but exact values vary by method, age, sex, dental status and symptoms.
Common adult teaching and clinical references often describe maximum mouth opening around 35–55 mm, with many people falling around 40–50 mm or higher.
Practical benchmarks:
Typical adult field range: approximately 40–55 mm
Functional opening for many daily and dental tasks: often around 35–40 mm or more
Reduced opening profile: below approximately 35–40 mm may be worth monitoring, especially with symptoms
Marked limitation: substantially below 30–35 mm may require closer assessment and appropriate referral consideration
These values should be treated as broad guides, not diagnostic cut-offs.
The most useful comparisons are often:
baseline to retest
comfortable versus maximum opening
active versus assisted opening
pain at end range
deviation pattern
chewing or yawning function
related cervical and TMJ findings
TMJ range-of-motion measurements are commonly used in jaw assessment and can be useful when measurement procedures are consistent.
Reliability improves when:
the same measurement landmarks are used
the same ruler or device is used
active and assisted measurements are labelled separately
comfortable and maximum opening are labelled separately
symptoms are recorded
joint sounds are documented
the same client position is used
the same endpoint definition is used
Validity depends on the purpose. TMJ depression measurement reflects mouth opening range under the chosen protocol. It does not identify the cause of reduced movement, diagnose a TMJ disorder, or determine whether symptoms are joint, muscle, dental or cervical in origin.
Small changes should be interpreted cautiously unless they are repeated and align with symptoms, function or related testing.
Common errors include:
not recording active versus assisted opening
not recording comfortable versus maximum opening
measuring from inconsistent landmarks
ignoring overbite or dental differences
forcing end range
not recording pain or symptoms
not recording deviation or joint sounds
comparing different measurement methods
using the result as a diagnosis
Limitations include:
dental landmarks may vary or be missing
pain and guarding may reduce opening
jaw deviation can affect measurement
overbite and tooth position may influence readings
client effort influences active opening
symptoms may fluctuate day to day
the test does not identify tissue source
the test does not determine treatment need on its own
Use TMJ depression measurement to:
establish baseline jaw opening
monitor jaw mobility over time
compare comfortable and maximum opening
track symptom response
record jaw deviation or joint sounds
support chewing, yawning and speaking assessment
decide whether related tests would add context
monitor progress after changes in symptoms, loading or function
It is most useful with:
TMJ translation
lateral jaw deviation
jaw closing control
cervical ROM
headache history
postural assessment
chewing tolerance
pain and symptom questionnaires
In Measurz, record the baseline opening measurement in millimetres.
Record:
active, comfortable, maximum or assisted opening
mouth opening in millimetres
pain score
symptom location
joint sounds
jaw deviation
dental landmarks used
client position
measurement tool
endpoint definition
stopping reason
retest date
Track progress across sessions and compare with TMJ translation, lateral deviation, cervical ROM, headache symptoms and functional notes such as chewing, speaking and yawning tolerance.
TMJ Translation
TMJ Lateral Deviation
Jaw Closing Control
Cervical Flexion
Cervical Extension
Cervical Rotation
Neck Flexion Rotation C1–2
Headache Disability Index
Neck Disability Index
Postural Assessment
It measures how far the mouth opens, usually recorded as maximum interincisal opening in millimetres.
Many adult references describe typical opening around 35–55 mm, with 40–50 mm commonly used as a practical clinical guide.
Measure the distance between the upper and lower central incisors during mouth opening.
Both can be useful. Comfortable opening and maximum active opening should be labelled separately.
It means the jaw opens less under the tested setup. It does not explain the cause by itself.
Yes. Record clicking, catching, locking, pain and deviation because they provide useful context.
No. It measures movement but does not diagnose the cause of jaw symptoms.
Use the same position, landmarks, measurement tool, opening instruction and symptom scale across sessions.
TMJ Depression measures jaw opening range.
The result is usually recorded as interincisal opening in millimetres.
Comfortable, active maximum and assisted opening should be labelled separately.
Broad reference values are useful, but baseline and retest comparison are often more practical.
Pain, clicking, catching, deviation and locking should be recorded.
Measurz should capture millimetres, symptoms, jaw deviation, joint sounds, test type and progress.
The test does not diagnose jaw symptoms or explain the cause on its own.
Dworkin, S. F., & LeResche, L. (1992). Research diagnostic criteria for temporomandibular disorders: Review, criteria, examinations and specifications, critique. Journal of Craniomandibular Disorders, 6(4), 301–355.
Kropmans, T. J. B., Dijkstra, P. U., Stegenga, B., Stewart, R., & de Bont, L. G. M. (1999). Smallest detectable difference in outcome variables related to painful restriction of the temporomandibular joint. Journal of Dental Research, 78(3), 784–789.
NICE Clinical Knowledge Summaries. (2024). Temporomandibular disorders: Assessment. National Institute for Health and Care Excellence.
Shaffer, S. M., Brismée, J.-M., Sizer, P. S., & Courtney, C. A. (2014). Temporomandibular disorders. Part 1: Anatomy and examination/diagnosis. Journal of Manual & Manipulative Therapy, 22(1), 2–12. https://doi.org/10.1179/2042618613Y.0000000060
Walker, N., Bohannon, R. W., & Cameron, D. (2000). Discriminant validity of temporomandibular joint range of motion measurements obtained with a ruler. Journal of Orthopaedic & Sports Physical Therapy, 30(8), 484–492. https://doi.org/10.2519/jospt.2000.30.8.484
