Assessment of Jaw Opening and Lateral Jaw Movement
Jaw Opening Assessment
For jaw opening assessment, resistance should be applied under the chin (submental region) in a downward direction while the patient attempts to open their mouth against this resistance. This tests the strength and function of the jaw-opening muscles, primarily the lateral pterygoid and suprahyoid muscle groups 1.
Technique for Jaw Opening Resistance
- Place your hand or fingers under the patient's chin and apply steady downward pressure while instructing the patient to open their mouth 1.
- The resistance should be applied in a controlled, gradual manner to allow assessment of muscle strength throughout the range of motion 2.
- Monitor for compensatory head extension movements, as patients may recruit neck extensors when jaw-opening muscles are weak or dysfunctional—an increased head/jaw ratio (>55% increase) during resistance suggests altered motor strategy and potential dysfunction 2.
- The patient should be able to maintain jaw opening against moderate resistance without significant deviation or pain 3.
Key Assessment Points
- Normal jaw-opening force in healthy individuals averages approximately 47.7 N, while patients with temporomandibular disorders demonstrate significantly reduced forces (approximately 18.5 N) 3.
- Observe for asymmetry or deviation during the movement, which may indicate unilateral muscle weakness or joint dysfunction 3.
- Assess maximum opening capacity before applying resistance—normal interincisal opening should be 40-50 mm 4.
Lateral Jaw Movement Assessment
For lateral jaw movement (excursion), resistance should be applied to the lateral aspect of the chin on the side toward which the jaw is moving. For example, when testing right lateral movement, apply resistance to the right side of the chin as the patient attempts to move the jaw to the right.
Technique for Lateral Movement Resistance
- Position your hand against the lateral surface of the chin on the side of intended movement 1.
- Apply steady lateral resistance while the patient attempts to move the jaw sideways against your hand 1.
- Test both directions separately (right and left lateral excursions) to identify unilateral weakness or asymmetry 3.
- Normal lateral excursion should be 8-12 mm to each side without significant resistance 4.
Critical Clinical Considerations
Cervical Spine Precautions
- Never use head-tilt/chin-lift maneuvers if cervical spine injury is suspected, as this produces three times more cervical movement than jaw thrust and can cause catastrophic cord injury 5.
- Use jaw thrust exclusively for airway management in trauma patients, as this produces significantly less cervical spine movement (mean 4.8° flexion-extension vs. 14.7° with head-tilt/chin-lift) 1.
- Maintain manual in-line stabilization during any jaw assessment if cervical spine injury cannot be excluded 5.
Common Pitfalls to Avoid
- Do not apply excessive force during resistance testing, as this can exacerbate temporomandibular joint dysfunction or cause patient discomfort 3.
- Avoid testing through pain—if the patient reports significant pain during resistance, this itself is a positive finding indicating dysfunction 3.
- Do not ignore compensatory movements—increased head movement during jaw opening with resistance (head/jaw ratio increase of 55.6%) indicates altered motor strategy and potential jaw-neck dysfunction 2.
- Recognize that passive positioning differs from active resistance testing—passive retruded positioning requires posterior pressure with passive hinge movement, which is distinct from active resistance testing 6.
Documentation Points
- Record the specific force applied and patient's ability to maintain position 3.
- Note any deviation patterns during opening or lateral movements 3.
- Document compensatory head movements that may indicate integrated jaw-neck dysfunction 2.
- Measure maximum opening before and after resistance to assess functional limitation 4.