Inferior Alveolar Nerve Block 

The inferior alveolar nerve block is the most common type of nerve block used for dental procedures. Knowledge of mouth and inferior alveolar nerve anatomy is required to perform the procedure.

See the image shown below.

The mandibular nerve exits at the base of the skull through the foramen ovale.

The first branch from the main trunk is the nervous spinosus, which runs superiorly through the foramen spinosum to supply the meninges.

The second branch is the first motor nerve, which supplies the medial pterygoid muscle. Inferior to that branch, the mandibular nerve splits into an anterior trunk (both sensory and motor) and a posterior trunk.

The motor component supplies the masseter, temporal, and lateral pterygoid muscles.

The posterior trunk radiates from the auriculotemporal nerve that gives sensory perception to the side of the head and scalp and sends twigs to the external auditory meatus, the tympanic membrane, and the temporomandibular joint. The posterior trunk then almost immediately divides into the lingual nerve and the inferior alveolar nerve.

The sensory trunk is the long buccal nerve that supplies the buccal soft tissue distal to the first molar.

The lingual nerve supplies the anterior two thirds of the tongue and the lingual surface of the mandibular gingiva.

The mandibular nerve sends a branch to the mylohyoid muscle and the anterior belly of the digastric muscle and then enters the mandibular canal. The mandibular nerve furnishes sensation to the following areas:

• Mandible
• Buccal gingiva anterior to the first molar
• Lower lip and the pulps of all the mandibular teeth in that quadrant

The inferior alveolar nerve is the larger branch of the posterior division of the mandibular nerve. The inferior alveolar nerve enters the mandibular foramen in the ramus of the mandible (see the image below) to occupy the inferior alveolar canal in the body of the mandible.

When the inferior alveolar nerve approaches the apex of the second bicuspid, it divides into two terminal branches, the mental and the incisive.

A nerve block of the intraoral mandibular or inferior alveolar nerve anesthetizes the following:

• The body of the mandible and the lower portion of the ramus
• All mandibular teeth
• The floor of the mouth
• The anterior two thirds of the tongue
• Gingivae on the lingual surface of the mandible
• Gingivae on the labial surface of the mandible
• Mucosa and skin of the lower lip and chin

Understanding the underlying anatomy of the pterygomandibular space helps increase the effectiveness of inferior alveolar nerve blocks.^[1]

An inferior alveolar nerve block is required to work in the following areas of the mouth:

• Mandibular teeth to the midline
• The anterior two thirds of the tongue
• The floor of the oral cavity

Absolute contraindication

• Hypersensitivity to local anesthetic agents, which occurs in less than 1% of the general population

Relative contraindication

• History of malignant hyperthermia

Various types and quantities of local anesthetic agents have been suggested for an inferior alveolar nerve block.

Monheim in 1961^[2] suggested 1.5-2 mL of solution. Prescribing information for articaine (Septocaine) recommends up to 3.4 mL for a nerve block,^[3] although Lemay in 1984^[4] suggested 3.6 mL. Prescribing information for lidocaine suggests up to 5 mL of lidocaine 2%,^[5] whereas Gaum recommends a minimum of 3.6 mL of lidocaine 2% with 1:100,000 concentration of epinephrine for inferior alveolar block anesthesia.^[6] Administering less may prove to be ineffective in many cases.

Generally, for temporary relief of pain prior to obtaining definitive dental care, the preferred agent is 0.5% bupivacaine (Marcaine, Sensorcaine) with 1:200,000 epinephrine. This provides 1-3 hours of dental pulp analgesia and 4-9 hours of soft tissue analgesia. Epinephrine prolongs duration of action through vasoconstriction at the injection site, which decreases systemic absorption.

Determining local anesthetic concentrations and dilutions

Concentrations: Drug concentration is expressed as a percentage (eg, bupivacaine 0.5%, lidocaine 1%).

• Percentage is measured in grams per 100 mL (ie, 1% is 1 g/100 mL [1000 mg/100 mL], or 10 mg/mL)

  • Calculate the mg/mL concentration quickly from the percentage by moving the decimal point 1 place to the right, as follows:
    • Bupivacaine 0.5% = 5 mg/mL
    • Lidocaine 2% = 20 mg/mL

Dilutions: When epinephrine is combined in an anesthetic solution, the result is expressed as a dilution (eg, 1:100,000).

• 1:100,000 means 1 mg per 100 mL (ie, 0.001%)
• 1:200,000 means 1 mg per 200 mL (ie, 0.0005%)

Table. Epinephrine Content Examples (Open Table in a new window)

Common local anesthetic agents for dental anesthesia

Articaine 4% (Septocaine) with epinephrine 1:100,000

• Adult total dose ranges for submucosal injection

  • Infiltrative administration: 0.5-2.5 mL (20-100 mg)
  • Nerve block: 0.5-3.4 mL (20-136 mg)
  • Oral surgery: 1-5.1 mL (40-204 mg)
  • Not to exceed 7 mg/kg (0.175 mL/kg)
• Decrease dose in pediatric patients (>4 y), elderly patients, or those with hepatic impairment; use in children younger than 4 y not recommended

Bupivacaine 0.5% (Sensorcaine)

• Maxillary and mandibular area for oral surgery
• Adult total dose range is 1.8 mL to a maximum of 18 mL (9-90 mg)
• Not to exceed 18 mL (90 mg) per dental sitting
• Reduce dose in pediatric or elderly patients, those with cardiac disease, those who are debilitated, or those with hepatic impairment

Lidocaine 2% (Xylocaine) with epinephrine 1:100,000 (or 1:50,000 when greater depth and hemostasis are required)

• Maxillary and mandibular area for oral surgery
• Adult total dose range for submucosal injection: 1-5 mL (20-100 mg)
• Children younger than 10 years: 0.9-1 mL (18-20 mg)
• Maximum dose for adult and pediatric patients

  • Not to exceed 7 mg/kg (with epinephrine)
  • Not to exceed 4.5 mg/kg (without epinephrine)

Mepivacaine 2-3% (Carbocaine, Polocaine)

• Also available with epinephrine 1:200,000 or levonordefrin 1:20,000; each prolongs duration of action
• Dental infiltration or nerve block
• Adult dose range

  • 2% with levonordefrin: 1.8 mL (36 mg)
  • Not to exceed 3 mg/kg or 400 mg in adults
  • 3%: 1.8 mL (54 mg)
  • Not to exceed 3 mg/kg or 400 mg in adults
• Pediatric dose: Not to exceed 9 mL (ie, 180 mg as the 2% solution or 270 mg as the 3% solution)

Prilocaine 4% (Citanest)

• Adult dose range: 1-2 mL (40-80 mg)
• Not to exceed 8 mg/kg or 600 mg within a 2-hour period
• Not to exceed 1 mL (40 mg) in children younger than 10 years

• Standard dental equipment should be present.
• The examination table or chair can be adjusted to accommodate the patient's height.
• An overhead light of sufficient intensity should be present.
• Sterile thumb-control syringe
• Topical anesthetic (in the form of pastes or gels)
• 2% lidocaine with epinephrine or 0.5% bupivacaine with epinephrine
• Cotton-tipped applicators to administer topical anesthetic and control bleeding
• Small-gauge (ga) needles (The longer the needle, the easier the inferior alveolar nerve block is to accomplish.)

  • 1 5/8 inch, 23 ga
  • 1 3/8 inch, 25 ga; some recommend 1 1/8 inch, 27 ga needle
  • 1 3/8 inch, 25 ga (probably the most popular choice of needle)

• Patients should be placed in a dental chair.
• The head should be tilted back.
• The patient should open his or her mouth.

The technique is as follows, based on the description of Powell:^[7]

• Apply topical anesthetic to the target area, which is the mucosa lateral to the pterygomandibular raphe but medial to the anterior border of the mandibular ramus and about 6-10 mm above the occlusal plane of the maxillary teeth.
• Place the thumb of the nondominant hand on the coronoid notch and the index finger just anterior to the ear to stretch the tissues over the injection site, maximizing visibility and minimizing the pain of the injection as depicted below. Holding back cheek
• With the anterior ramus technique, palpate the anterior border of the ramus with the thumb and find the greatest concavity, which is the coronoid notch.^[6]
• Orient the syringe so that the barrel is in the opposite corner of the mouth, resting on the premolars.
• With the anterior ramus technique, use the middle finger and thumb to determine the width of the ramus in its anterior-posterior dimension. Anatomically, the mandibular foramen lies in the middle of the ramus in this dimension. The average width of the ramus, including the thickness of the soft tissue in the coronoid notch, is approximately 35 mm, which is also the length of the needle.^[6]
• Aim toward the index finger and slowly penetrate the mucosa until bone is contacted.

  • Bone is usually contacted within about 2.5 cm.
  • If the attempt does not result in contact with bone, reorient the syringe more laterally and repeat attempt.
• Withdraw slightly and aspirate.

  • Rotate the bevel of the needle and re-aspirate; if no blood is returned, inject 1.5-2 mL of anesthetic.
  • If aspiration is positive, pull back about 5 mm and redirect slightly, then repeat attempt at aspiration.
• If the injection fails to result in adequate analgesia, it may safely be repeated 2 additional times.
• Patients often report mild jaw muscle soreness for 2-3 days following this injection.

• Anatomic landmarks are important to note.
• An appropriate needle should be used.
• Understanding and palpating landmarks is critical in a successful attempt.

• A failure rate of 15-20% is seen, even in experienced hands.
• With an unsuccessful attempt, the patient experiences pain with no therapeutic benefit.
• Inadequate anesthesia may also result from the formation of a blood clot due to the traumatized, lacerated, and bleeding vessel. The blood from the formation of a hematoma may dilute the local anesthetic solution. This may weaken the anesthetic effects.
• Fracture of a dental needle while performing an inferior alveolar nerve block has been reported.^[8]
• Trismus and sensory deficit following resolution of trismus have been reported in 2 patients as delayed complications of inferior alveolar nerve block.^[9]
• Medial pterygoid trismus i.e. myospasm occurring after inferior alveolar nerve block has occurred.^[10]