How do dentists determine if wisdom teeth are close to or sitting on the inferior alveolar nerve (IAN)?

Diagnostic Imaging for Wisdom Teeth Near Nerves: Assessment and Implications

Dentists determine if wisdom teeth are close to or sitting on the inferior alveolar nerve primarily through CBCT imaging, which is essential for accurately assessing the relationship between third molars and the mandibular canal to prevent nerve injury during extraction. 1, 2

Diagnostic Imaging Process

Initial Assessment

• Orthopantomography (panoramic X-ray) should be the first diagnostic examination for suspected dental impaction 1, 2
• Panoramic X-rays provide initial information on:
  • Position of the impacted tooth
  • Relationship with the alveolar ridge
  • Projective relationships with adjacent teeth and structures
  • Presence of associated lesions 1

When CBCT Is Indicated

• CBCT is essential when panoramic imaging suggests contact between:
  • Third lower molars and the mandibular canal
  • Third upper molars and the maxillary sinus floor 1, 2
• 2D imaging techniques are significantly inferior to 3D CBCT in assessing relationships between impacted teeth and critical anatomical structures 1
• CBCT should be targeted to reduce radiation exposure following the ALARA principle (As Low As Reasonably Achievable) 1, 2

The Inferior Alveolar Nerve

The inferior alveolar nerve (IAN) is the nerve at risk during wisdom tooth extraction. This nerve:

• Runs through the mandibular canal in the lower jaw
• Provides sensation to the lower teeth, lower lip, and chin
• Is a branch of the mandibular division of the trigeminal nerve (fifth cranial nerve) 1

Implications of Nerve Damage

Damage to the inferior alveolar nerve during wisdom tooth extraction can result in:

• Temporary or permanent neurosensory disturbances 3
• Numbness, tingling, or altered sensation in the lower lip and chin
• Decreased quality of life due to functional and sensory impairment
• Difficulty with speech, eating, and drinking without biting the lip 4

Risk Assessment and Surgical Planning

Radiographic Risk Indicators

Specific radiographic signs that indicate higher risk of nerve damage include:

• Darkening of the wisdom tooth root
• Presence of two or more specific radiographic signs of proximity 4
• Interruption of the white line representing the mandibular canal 5

Surgical Decision Making

• CBCT contributes to optimal risk assessment and more adequate surgical planning compared to panoramic radiography alone 5
• In cases with high risk of nerve damage, alternative approaches may be considered:
  • Coronectomy (partial tooth removal leaving the roots intact) can significantly reduce the prevalence of nerve damage 4
  • Modified surgical techniques based on precise anatomical knowledge 2

Clinical Considerations and Limitations

• Despite improved imaging, nerve damage can still occur even with CBCT guidance 6
• A randomized controlled trial showed that for "moderate-risk" cases, CBCT was not significantly better than panoramic radiography in predicting postoperative complications 6
• The extremely large sample sizes required to prove CBCT superiority for preventing nerve damage suggests that routine CBCT should be reserved for high-risk wisdom tooth removals 3

Practical Approach to Imaging Selection

1. Start with panoramic radiography for all impacted wisdom teeth
2. If panoramic imaging shows no overlap between the mandibular canal and wisdom tooth, no additional imaging is needed 7
3. If panoramic imaging suggests proximity to the mandibular canal, CBCT is indicated 1, 2
4. Use targeted CBCT with appropriate field of view to minimize radiation exposure 1, 2

By following this evidence-based approach to imaging selection and surgical planning, dentists can minimize the risk of nerve damage during wisdom tooth extraction while avoiding unnecessary radiation exposure.