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The inferior alveolar nerve block is the second most frequently used (after infiltration) and possibly the most important injection technique in dentistry.  Unfortunately, it also proves to be the most frustrating with the highest percentage of clinical failures even when properly administered.  Administration of bilateral inferior alveolar nerve blocks is rarely indicated and highly discouraged.  They produce a considerable amount of discomfort, primarily from the lingual soft tissue anesthesia.  The patient feels unable to swallow and, because of the absence of all sensation, is more likely to self-injure the anesthetized soft tissues.  Additional residual soft tissue anesthesia affects the patient's ability to speak and to swallow.   

The nerves that are anesthetized are the inferior alveolar (a branch of the posterior division of the mandibular division of the trigeminal nerve (V3), incisive, mental, and lingual).  The areas anesthetized include the mandibular teeth to the midline, the body of the mandible, inferior portion of the ramus, buccal mucoperiosteum, mucous membrane anterior to the mental foramen (mental nerve), anterior 2/3 of the tongue and floor of the oral cavity (lingual nerve), and lingual soft tissues and periosteum (lingual nerve).  

Proper technique:

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  1. 25-gauge long needle is recommended 

  2. Area of insertion: mucous membrane on the medial (lingual) side of the mandibular ramus, at the intersection of two lines- horizontal (height of needle insertion and vertical (anteroposterior plane of injection)

  3. Target area: inferior alveolar nerve as it passes downward toward the mandibular foramen but before it enters into the foramen

  4. Landmarks

    • Coronoid notch (greatest concavity on the anterior border of the ramus)​

    • Pterygomandibular raphe (vertical portion)

    • Occlusal plane of the mandibular posterior teeth

  5. Orientation of the bevel: less critical than with other nerve blocks, because the needle approaches the inferior alveolar nerve at roughly a right angle 

Procedures:

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  1. Correct patient & clinician positioning

    • Right IA/Li, right-handed clinician sit at 8:00 facing patient / left-handed clinician sit at 4:00 facing patient 

    • Left IA/Li, right-handed clinician sit at 10:00 facing in the same direction as the patient  / left-handed clinician sit at 2:00 facing in the same direction as the patient

    • Position patient supine (recommended) or semisupine (if necessary) 

  2. The mouth should be opened wide to allow greater visibility of, and access to, the injection site

  3. Locate and prepare the injection site

    • Dry with gauze or blow air with air/water syringe​

    • Apply topical anesthetic for minimum of 1 minute

  4. When locating the injection site, three parameters must be considered: height of the injection, anteroposterior placement of the needle (which helps to locate a precise needle entry point), and depth of penetration (which determines the location of the inferior alveolar nerve)

    • Height of injection: place the index finger or the thumb of your opposite hand in the coronoid notch​

      • An imaginary line extends posteriorly from the fingertip in the coronoid notch to the deepest part of the pterygomandibular raphe (as it turns vertically upward toward the maxilla), determining the height of injection.  The imaginary line should be parallel to the occlusal plane of the mandibular molar teeth.  In most patients, this line lies 6-10mm above the occlusal plane​

      • The finger on the coronoid notch is used to pull the tissues laterally, stretching them over the injection site, making them taut, and enabling needle insertion to be less traumatic, while providing better visibility

      • The needle insertion point lies 3/4 of the anteroposterior distance from the coronoid notch back to the deepest part of the pterygomandibular raphe

      • The posterior border of the mandibular ramus can be approximated intraorally by using the pterygomandibular raphe as it bends vertically upward toward the maxilla

      • Prepare the injection site

        • Dry with gauze or blow air with air/water syringe​

        • Apply topical anesthetic for 1-2 minutes

      • Place the barrel of the syringe in the corner of the mouth on the contralateral side 

    • Anteroposterior site of injection: needle penetration occurs at the intersection of two points

      • Point 1: along the horizontal line from the coronoid notch to the deepest part of the pterygomandibular raphe as it ascends vertically toward the palate​

      • Point 2: vertical line through point 1 about 3/4 of the distance from the anterior border of the ramus

    • Penetration depth: bone should be contacted.  Slowly advance the needle until you can feel it meet bony resistance.

      • For most patients, it is not necessary to inject any local anesthetic solution as soft tissue is penetrated​ (can be deposited in small volumes for anxious and sensitive patients)

      • Average depth of penetration to bony contact will be about 20-25mm (about 2/3 to 3/4 the length of the long needle 

      • Needle tip should now be located slightly superior to the mandibular foramen

      • If the bone is contacted too soon (less than 1/2 the length of a long needle), the needle tip is usually located too far anteriorly (laterally) on the ramus

        • To correct:​

          • Withdraw needle slight​ly but do not remove it from tissue

          • Bring syringe barrel more toward front of the mouth, over the canine or lateral incisor on the contralateral side

          • Redirect needle until a more appropriate depth of insertion is obtained.  The needle tip is now located more posteriorly in the mandibular sulcus 

      • If bone is not contacted, needle tip usually is located too far posterior (medial)

        • To correct:​

          • Withdraw it slightly in tissue (leaving approximately 1/4 ​its length in tissue) and reposition the syringe barrel more posteriorly (over the mandibular molars)

          • Continue needle insertion until contact with bone is made at an appropriate depth (20-25mm)

  5. Once the needle is inserted and bone is contacted, withdraw approximately 1mm to prevent subperiosteal injection

  6. Aspirate in two planes​​

  7. If negative, slowly deposit 0.9-1.5mL of anesthetic solution (1/2 to 2/3 cartridge) approximately 60 seconds 

  8. Slowly withdraw needle until half the length of the needle remains within the tissues, reaspirate

  9. If negative, deposit a portion of the remaining 0.2-0.6mL solution to anesthetize the lingual nerve

  10. Slowly withdraw needle and safely recap

  11. After about 20 seconds, return the patient to the upright or semisupine position

  12. Wait a minimum of 3-5 minutes before testing for pulpal anesthesia 

I N F E R I O R   A L V E O L A R  /  L I N G U A L   ( I A / L i ) 

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