Mandibular Nerve and Inferior Alveolar Nerve Block

Mandibular Nerve

• The mandibular nerve is a branch of the trigeminal nerve
• It has an undivided nerve and a divided nerve with anterior and posterior divisions
• The undivided nerve includes the nerve to the medial pterygoid muscle and the nervus spinosus
• The anterior division include: nerve to lateral pterygoid muscle, nerve to masseter muscle, nerve to temporal muscle and buccal nerve
• The posterior division includes: auriculotemporal nerve, lingual nerve, mylohyoid nerve, inferior alveolar nerve with dental branches, and incisive branch with dental branches and mental nerve

Inferior Alveolar Nerve Block

Nerves Anesthetized

• Inferior alveolar nerve
• Incisive nerve
• Mental nerve
• Lingual nerve (commonly)

Indications

• Procedures on multiple mandibular teeth in one quadrant
• When buccal soft-tissue anesthesia is needed (anterior to the first molar)
• When lingual soft-tissue anesthesia is needed

Contraindications

• Infection or acute inflammation in the injection area (rare)
• Patients who might bite the lip or tongue (e.g., young children, physically or mentally challenged adults)

Advantages

• One injection provides a wide area of anesthesia (useful for quadrant dentistry)

Disadvantages

• Wide area of anesthesia (not necessary for localized procedures)
• Rate of inadequate anesthesia (15% to 20%)
• Intraoral landmarks are not consistently reliable
• Positive aspiration (10% to 15%, highest rate of all intraoral injection techniques)
• Lingual and lower lip anesthesia, potentially discomforting
• Partial anesthesia possible with bifid inferior alveolar nerve and bifid mandibular canals

Alternatives

• Mental nerve block (buccal soft-tissue anesthesia anterior to the first molar)
• Incisive nerve block (pulpal and buccal soft-tissue anesthesia of teeth anterior to the mental foramen)
• Supraperiosteal injection (pulpal anesthesia of central and lateral incisors, and sometimes premolars)
• Gow-Gates mandibular nerve block
• Vazirani-Akinosi mandibular nerve block
• PDL injection (pulpal anesthesia of any mandibular tooth)
• Intraosseous (IO) injection (osseous and soft-tissue anesthesia of any mandibular region, especially molars)
• Intraseptal injection (osseous and soft-tissue anesthesia of any mandibular region)

Technique

• 25-gauge long needle recommended for adult patients
• Area of insertion: mucous membrane on medial side of mandibular ramus, at the intersection of horizontal and vertical lines

Landmarks

• Coronoid notch (greatest concavity on anterior border of the ramus)
• Pterygomandibular raphe
• Occlusal plane of mandibular posterior teeth

Operator Position

• Right-handed administrator sits at 8 o'clock position, facing patient

Positioning the patient

• Supine or semi-supine
• Head positioned so mandible is parallel to the floor when mouth is open

Palpation of Intraoral Landmarks

• Palpate mucobuccal fold with left index finger or thumb
• Move finger/thumb posteriorly to external oblique ridge on anterior border of mandibular ramus
• Move finger/thumb up and down to identify coronoid notch (in line with mandibular sulcus)
• Move finger lingually across retromolar triangle and onto internal oblique ridge

Needle Insertion

• Syringe with 1 5/8 inch, 25-gauge needle
• Insert parallel to the occlusal plane of mandibular teeth, opposite side of the mouth
• Bisect finger/thumb level, penetrate pterygotemporal depression, enter pterygomandibular space
• Patient should keep mouth wide open during insertion
• Penetrate tissues to the internal surface of the mandibular ramus to make bony contact
• Average depth of penetration is 20-25mm (approximately two-thirds to three-fourths length of long dental needle)

Technique: Right Inferior Alveolar Nerve Block

• Withdraw approximately 1 mm when bone is contacted to prevent subperiosteal injection
• Aspirate in two planes
• If negative, deposit 1.5 mL of anesthetic over 60 seconds (slow injection, reaspiration, slow injection, reaspiration is recommended)
• Slowly withdraw syringe; reaspirate when approximately half length remains within tissues
• Deposit a portion of the remaining solution (0.2 mL) to anesthetize the lingual nerve (often not necessary)

Technique: Left Inferior Alveolar Nerve Block

• Right-handed administrator sits at 10 o'clock position, facing patient
• Left arm of dentist placed around patient's head for palpating landmarks with left index finger or thumb

Signs and Symptoms

• Subjective: Tingling or numbness of lower lip (mental nerve)
• Subjective: Tingling or numbness of tongue (lingual nerve)
• Objective: Use of freezing spray/electric pulp tester (EPT) showing no response after maximal output (80/80) for two tests (at least 2 minutes apart) - considered a "guarantee" (approximately 99%)
• Objective: No pain during dental therapy

Precautions

• Don't deposit local anesthetic if bone is not contacted (needle tip could be in parotid gland near facial nerve, leading to transient paralysis)
• Avoid forcefully contacting bone

Failures of Anesthesia

• Deposition of anesthetic too low (below mandibular foramen)
• Deposition of anesthetic too far anteriorly/laterally on the ramus
• Accessory innervation to the mandibular teeth

Complications

• Hematoma (rare): swelling of tissues on medial side of mandibular ramus; manage with pressure and cold
• Trismus (rare): muscle soreness, limited movement, may be slight or severe
• Transient facial paralysis: local anesthetic deposition into parotid gland; inability to close lower eyelid, drooping upper lip