Why Does My Jaw Deviate to One Side When I Open?
Stand in front of a mirror and slowly open your mouth.
Does your chin travel straight down, or does it shift to one side?
Some people notice that their jaw moves sideways and then comes back toward the middle. Others notice that it gradually moves toward one side and stays there.
This can happen for several reasons, and the way the jaw moves can give us useful clues about what the two temporomandibular joints (TMJs) are doing.
But there is an important distinction:
A jaw that deviates is showing us a movement pattern, not giving us a diagnosis.
Why Should the Jaw Normally Stay Near the Middle?
Your lower jaw is one bone controlled by two TMJs, one on each side of your head.
During mouth opening, each mandibular condyle initially rotates and then progressively translates forward and downward along the articular surface. The right and left sides have to coordinate these movements.
When the two condyles move with reasonably similar timing and excursion, the chin tends to remain relatively close to the midline.
If one condyle translates differently from the other, however, the mandible can rotate slightly in the horizontal plane, and the chin moves sideways.
That is the basic biomechanical reason a jaw deviates.
Deviation: The Jaw Moves Sideways, Then Comes Back
Imagine that during opening the left condyle begins translating forward sooner or farther than the right.
Because the two condyles are attached to the same mandible, the jaw cannot simply open with one side moving forward independently. The difference between the two sides produces a temporary rotation of the mandible, and the chin shifts toward the side that is moving less.
If the slower side subsequently catches up, the right and left condyles become more symmetrical again and the chin returns toward the middle.
Clinically, this is often described as a deviation.
So when we see:
sideways → then back toward centre
we are often thinking about a temporary difference in the timing or coordination of condylar translation.
Several things could potentially produce that pattern.
One possibility is disc displacement with reduction. In this situation, the disc-condyle relationship is altered when the mouth is closed. During opening, the condyle may move differently until the disc reduces, after which translation can continue more normally. This can produce clicking and altered or asynchronous jaw movement.
Research examining three-dimensional jaw movement in people with disc displacement with reduction has demonstrated greater asynchrony between the two condyles during opening and closing.
But disc displacement is only one possible explanation. Differences in joint mobility, pain-related guarding, and motor coordination can also alter the timing of movement.
This is why we cannot look at a deviation and simply say, “Your disc is displaced.”
Deflection: The Jaw Moves Sideways and Stays There
A different pattern occurs when the jaw gradually moves toward one side and does not return toward the centre at the end of opening.
This is commonly described clinically as a deflection.
Biomechanically, this suggests something somewhat different.
If one condyle continues translating normally while the other has less forward translation, the difference between the two sides remains throughout opening. The mandible therefore continues to rotate toward the side with less movement.
For example, if the right condyle translates less than the left, the chin will generally deflect toward the right.
So a useful clinical principle is:
Persistent deflection tends to occur toward the side with reduced condylar translation.
Why might that condyle translate less?
Possible contributors include:
joint hypomobility,
pain and protective guarding,
disc displacement without reduction,
muscular restriction or altered motor control,
joint degenerative or structural changes,
or previous trauma.
Again, the direction of the jaw gives us a biomechanical clue, but it does not tell us which of these explanations is responsible.
Why Can a Disc Problem Change the Path of Opening?
The articular disc sits between the mandibular condyle and the temporal bone and normally moves as part of the disc-condyle complex.
With disc displacement with reduction, the disc is displaced when the mouth is closed but returns to a more normal relationship with the condyle during opening.
The condyle may therefore translate less smoothly until reduction occurs. Once the disc reduces, movement can become freer, allowing the previously lagging side to catch up.
That helps explain why some people demonstrate a:
shift → click → return toward midline
pattern.
With disc displacement without reduction, the disc does not return to its usual relationship during opening. In some presentations, this can interfere with condylar translation and contribute to restricted opening and persistent deflection toward the more restricted side.
However, these patterns are not sufficiently specific to diagnose disc displacement without a complete clinical assessment.
The Muscles and Nervous System Matter Too
The TMJ is not simply a mechanical hinge.
Jaw movement requires coordinated activity from the muscles of mastication and other muscles involved in mandibular and hyoid control. Pain can also change how the nervous system organizes movement.
Someone with a painful joint or muscle may unconsciously protect that side, altering the speed, timing, or amount of condylar movement.
This means that two people whose jaws deviate in the same direction may have very different reasons for doing so.
That is why treating every crooked opening by simply telling the patient to “open straight” misses the bigger picture.
What About the Neck?
The cervical and jaw systems are functionally related, and neck pain and TMD frequently coexist. Cervical movement, headache, muscle function, and sensorimotor control may therefore be relevant in some patients, particularly following injuries such as motor vehicle collisions.
But we should be careful not to oversimplify this relationship.
A forward-head posture does not automatically explain a jaw deviation, and seeing an asymmetrical jaw does not mean that the neck caused the problem.
The cervical region should be assessed when the patient's symptoms and examination suggest that it is clinically relevant.
When Does Jaw Deviation Matter?
A small, painless deviation does not automatically require treatment.
It becomes more important when the movement is new, progressively changing, or accompanied by:
pain,
restricted mouth opening,
catching or locking,
painful clicking,
difficulty chewing,
a change in bite,
or symptoms following trauma.
In those situations, the opening pathway becomes one useful part of a larger TMJ assessment.
We look at where the jaw moves, when it deviates, whether it returns to midline, how far each side moves, whether clicking occurs at the same point, whether movement is restricted, and whether the pattern changes with repeated opening.
Together, those findings tell us much more than the direction of deviation alone.
The Bottom Line
When your jaw moves to one side during opening, the simplest biomechanical explanation is that the two sides of the jaw are not moving forward with exactly the same timing or amount.
If the jaw moves sideways and then returns toward the centre, the difference may be temporary—the slower side eventually catches up.
If the jaw progressively moves toward one side and stays there, there may be a more persistent difference in translation between the two TMJs.
Disc mechanics, joint mobility, pain, muscle function, motor control, and previous injury can all potentially contribute.
The important point is that the movement pattern tells us where to investigate—it does not, by itself, tell us the diagnosis.
A good TMJ assessment therefore doesn't simply ask:
“Which way does your jaw move?”
It asks:
“Why are the two sides moving differently?”
And that is usually the more useful question.
References:
Armijo-Olivo, S., Pitance, L., Singh, V., Neto, F., Thie, N. M. R., & Michelotti, A. (2016). Effectiveness of manual therapy and therapeutic exercise for temporomandibular disorders: Systematic review and meta-analysis. Physical Therapy, 96(1), 9–25.
Mapelli, A., Machado, B. C. Z., Garcia, D. M., Rodrigues Da Silva, M. A. M., & Sforza, C. (2016). Three-dimensional analysis of jaw kinematic alterations in patients with chronic TMD—disc displacement with reduction. Journal of Oral Rehabilitation, 43(11), 824–832.
Poluha, R. L., Canales, G. T., Costa, Y. M., Grossmann, E., Bonjardim, L. R., & Conti, P. C. R. (2019). Temporomandibular joint disc displacement with reduction: A review of mechanisms and clinical presentation. Journal of Applied Oral Science, 27, e20180433.
Schiffman, E., Ohrbach, R., Truelove, E., et al. (2014). Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) for clinical and research applications: Recommendations of the International RDC/TMD Consortium Network and Orofacial Pain Special Interest Group. Journal of Oral & Facial Pain and Headache, 28(1), 6–27.
