What diagnostic studies are used for a patient with a locked jaw?

Diagnostic Studies for a Locked Jaw

The primary diagnostic studies for a patient with a locked jaw should include periapical intraoral radiographs and, if needed, cone beam computed tomography (CBCT) to evaluate the temporomandibular joint and surrounding structures. 1

Initial Diagnostic Approach

Clinical Evaluation

• Assess for:
  • Limitation of mandibular movements
  • Pain on palpation of the temporomandibular joint
  • Altered dental occlusion
  • Facial asymmetry
  • Deviation of the chin towards the affected side during mouth opening 2

First-Line Imaging

1. Periapical Intraoral Radiography

   • Gold standard for initial assessment of localized dental/jaw problems
   • Should be performed with an adequate paralleling system
   • Provides sufficient information for treatment planning in most cases 1
   • Higher spatial resolution compared to panoramic radiographs for localized issues

2. Orthopantomography (OPG/Panoramic X-ray)

   • Consider if multiple areas need to be visualized
   • Sensitivity of 86-92% for mandibular fractures 2
   • Advantages: includes both jaws in one image with reduced radiation exposure
   • Not recommended for localized trauma due to lower resolution 1

Advanced Imaging (When First-Line Is Insufficient)

Cone Beam Computed Tomography (CBCT)

• Indicated when:
  • 2D imaging is insufficient to clarify anatomical relationships
  • Root fracture or alveolar bone fracture is suspected
  • Evaluation of the fracture line on the buccal-lingual plane is needed
  • Assessment of tooth luxation is required 1
  • Relationship between mandibular structures and canal needs evaluation 1

Magnetic Resonance Imaging (MRI)

• Gold standard for temporomandibular joint (TMJ) soft tissue evaluation
• Specifically indicated for:
  • Detection of active TMJ arthritis
  • Evaluation of disc displacement
  • Assessment of joint effusion 1
• Contrast-enhanced MRI is the best method to detect active TMJ inflammation 1

Diagnostic Algorithm for Locked Jaw

1. For suspected TMJ disorder or dysfunction:

   • Begin with periapical radiographs
   • If findings are inconclusive → proceed to CBCT
   • If soft tissue involvement is suspected → consider MRI, especially contrast-enhanced 1

2. For suspected mandibular fracture:

   • Initial OPG for overview
   • CT scan with multiplanar reconstructions for definitive diagnosis (sensitivity nearly 100%) 2
   • Verify no associated fractures (mandibular fractures present in pairs in 67% of cases) 2

3. For suspected dental trauma:

   • Periapical intraoral radiographs as first choice
   • CBCT if root fracture or alveolar bone fracture is suspected 1

Important Considerations

• Follow the ALARA principle (As Low As Reasonably Achievable) when ordering radiographic studies
• CBCT imaging should be as targeted as possible to minimize radiation exposure while maintaining optimal spatial resolution 1
• Consider that locked jaw may be related to non-traumatic causes such as TMJ arthritis, which requires different imaging approaches 1
• In cases of neuropathic facial pain or burning mouth syndrome, imaging may be normal, and diagnosis relies more on clinical features 1

Pitfalls to Avoid

• Relying solely on 2D imaging for complex cases involving the temporomandibular joint
• Overlooking the possibility of paired mandibular fractures when one is identified
• Failing to consider non-traumatic causes of locked jaw (arthritis, myofascial pain, etc.)
• Using OPT/panoramic imaging for localized trauma (higher risk of movement artifacts and lower resolution) 1
• Neglecting to evaluate for nerve injury when fractures involve the mandibular canal 2

By following this diagnostic approach, clinicians can accurately identify the cause of a locked jaw and develop an appropriate treatment plan to address the underlying condition.