How do you elicit normal temporomandibular joint (TMJ) mobility?

How to Elicit Normal Temporomandibular Joint (TMJ) Mobility

Normal TMJ mobility is assessed by measuring maximum interincisal mouth opening (MMO), which should be ≥40mm in healthy adults, combined with evaluation of lateral excursions (≥7mm bilaterally) and protrusive movement (≥7mm). 1

Primary Assessment Method: Linear Mouth Opening (LMO)

• Measure the interincisal distance at maximal mouth opening and add the vertical overlap (overbite) of the dentition to obtain the true linear mouth opening measurement 1
• Normal values: ≥40mm for adults without TMJ disorders 2
• This is the most practical and widely used clinical method for assessing TMJ mobility 1

Supplementary Mobility Assessments

Lateral Excursion Testing

• Measure lateral jaw movement to both right and left sides 3
• Normal lateral excursion: ≥7mm bilaterally 3
• Asymmetry >2mm between sides may indicate unilateral TMJ dysfunction 3

Protrusive Movement

• Assess forward mandibular movement from maximum intercuspation 3
• Normal protrusive range: ≥7mm 3

Angular Mouth Opening (AMO)

• Measure angular displacement of the mandible relative to the cranium at maximal mouth opening 1
• This method strongly correlates with linear mouth opening (r = 0.71) 1
• AMO is significantly influenced by mandibular length, making it useful for comparing mobility across different facial morphologies 1

Clinical Examination Technique

Patient Positioning

• Position the patient seated upright with head in neutral position 3
• Ensure relaxed posture to avoid muscle guarding that may limit opening 3

Measurement Protocol

• Use a millimeter ruler or digital caliper for precise measurement 1, 2
• Measure from the incisal edge of the maxillary central incisor to the incisal edge of the mandibular central incisor 1
• Add the vertical overlap (overbite) to obtain true TMJ mobility 1
• Perform three measurements and record the maximum value 2

Assessment of Movement Quality

• Observe the opening pathway for deviation or deflection 3
• Deviation: temporary shift from midline that self-corrects during opening 3
• Deflection: persistent shift from midline throughout opening, suggesting disc displacement or structural asymmetry 3
• Palpate the TMJ bilaterally during opening to detect clicking, crepitus, or asymmetric condylar translation 3

Advanced Assessment Methods

Condylar Mobility Assessment

• Radiographic assessment of condylar position relative to the articular eminence can be performed using transpharyngeal radiographs 1
• Condylar mobility strongly correlates with angular mouth opening (r = 0.72) but weakly with linear mouth opening (r = 0.42) 1
• This method is reserved for cases where structural pathology is suspected 1

Radiographic Angle of Mouth Opening (RAMO)

• Measure angular displacement on transpharyngeal radiographs comparing closed and maximally opened positions 1
• No significant difference exists between clinical AMO and radiographic RAMO, making clinical measurement sufficient for most cases 1

Standardized Approach for Longitudinal Monitoring

• Use a standardized clinical examination protocol to monitor changes over time 3
• The American Academy of Oral Medicine recommends regular reassessment of TMJ mobility in patients with TMJ disorders 3
• Document baseline measurements and track changes at each follow-up visit 3
• Surface electromyography (SEMG) of masseter muscles can serve as an adjunctive tool to assess therapeutic effectiveness in patients with restricted mobility 4

Common Pitfalls to Avoid

• Do not rely solely on patient-reported symptoms, as TMJ dysfunction is often asymptomatic 3
• Failing to add the vertical overlap to interincisal distance underestimates true TMJ mobility 1
• Avoid assessing mobility when acute pain or muscle spasm is present, as this artificially limits opening 3
• Do not compare measurements across patients without considering mandibular length, as this significantly influences absolute opening values 1

Clinical Context

• Approximately 85-90% of TMJ disorders are muscular in origin rather than true intra-articular pathology 5
• Only 5% represent genuine joint pathology requiring advanced imaging or surgical intervention 5
• Reduced mobility (<40mm) combined with myofascial pain indicates hypomobility requiring conservative management 2
• Manual therapy and jaw exercises are strongly recommended first-line interventions for restricted TMJ mobility 3, 4