“How wide can you open your mouth?” Pretty straightforward question, right?
But during a TMJ examination, the range of motion of your jaw can tell us a lot about what is happening around and inside your joint, as well as within the muscles that control it.
The point is not just how many millimetres you can open. Rather, we look at how you open, how far you open, whether it hurts, whether the movement is smooth, whether the jaw deviates, whether there are sounds, and whether the movement feels restricted or excessive.
So, what is considered normal? In an Indian adult, a comfortable mouth opening is generally approximately 42 mm, without pain, discomfort or significant joint sounds.
What if my mouth doesn’t open enough?
It is something that needs to be investigated. Reduced opening can occur for many different reasons which may or may not be related to the TMJ.
If TMJ Related, it could be because of –
- Masticatory muscle contraction or spasm
- Disc displacement without reduction
- Coronoid hyperplasia
- TMJ Ankylosis
It could also be non-TMJ related like –
- Trauma
- Oral submucous fibrosis
- Space-occupying or malignant growths
- Other structural or inflammatory conditions
And this is where checking the way your jaw is restricted becomes important.
A sudden change in opening pattern, particularly when accompanied by a history of clicking that has disappeared, can occur with disc displacement without reduction.
This is one reason why a patient saying:
“My jaw used to click, and now it doesn’t, but now I can’t open properly.” is clinically important.
Another important question, What if the jaw opens too much?
Some people have hypermobility or increased ligamentous laxity, allowing the condyle to translate excessively. In susceptible individuals, this can contribute to:
Subluxation
Open-lock episodes
TMJ dislocation
A sensation that the jaw is “slipping out”
Difficulty closing the mouth after very wide opening
We want to know whether that movement is controlled and stable. The way your jaw opens matters too. If you notice, your jaw doesn’t always travel perfectly straight.
During opening, we observe whether it:
- Opens straight – relatively symmetrical movement
- Deviates and then returns toward the midline – may provide clues about movement of the condyles and disc
- Deflects consistently to one side – may indicate restriction or altered movement on that side
The direction, timing and extent of deviation can provide useful information when combined with the rest of the examination.
About side-to-side movement-
Also called lateral excursion – how far your lower jaw can move to either side. About 1-2mm each side is considered normal. And we don’t look at the movement in isolation. We compare right and left movements, observe the quality of movement and assess whether the restriction is associated with pain, joint sounds or muscular tenderness.
So what are we really assessing?
When we measure your jaw opening, the question is not if you can open exactly 42 mm
We’re asking:
- How far?
- How smoothly?
- How symmetrically?
- With or without pain?
- With or without clicking or crepitus ?
- Does the jaw deviate?
- Is there a hard or soft endpoint?
- Can you move comfortably from side to side?
- Is the movement restricted or excessive?
- Has your range of motion changed over time?
All of these pieces together help us understand what’s happening with the TMJ, disc, muscles, ligaments and surrounding structures.
Your jaw’s range of motion isn’t just a number. It’s a window into how your jaw is functioning.