Inferior Alveolar Nerve block – Local Anesthesia Technique, Landmarks and Symptoms

It is sometimes called the Inferior Dental Nerve which gives off a motor branch supplying the Mylohyoid and the anterior belly of digastric and travels through the Mandibular foramen and enters the Mandible. After entering the Mandible it supplies to the following Mandibular Teeth: 2^nd Premolar, 1^st, 2^nd, and 3^rd Molars.

It extends Anteriorly forming the Mental Nerve at the level of Mandibular 2^nd Molar roots exiting the mandible through the Mental foramen. And Supplying Sensory nerve fibres to the Chin and Lower lip of that Side. It further extends anteriorly as the mandibular incisive nerve to supply the Mandibular incisors and Canine.

Anatomical Landmarks of Inferior alveolar nerve block:

1. Mucobuccal fold
2. Anterior border of Mandibular ramus
3. External oblique ridge
4. Internal oblique ridge
5. Retromolar triangle
6. Pterygomandibular ligament
7. Buccal sucking pad
8. Pterygomandibular space

Nerves Anesthetized by Inferior alveolar nerve block:

Inferior Alveolar Nerve and its Sub-divisions

1. Mental Nerve
2. Incisive Nerve
3. Lingual Nerve
4. Buccinator Nerve

Areas Anesthetized by Inferior alveolar nerve block:

1. Body of Mandible and an inferior portion of the ramus
2. Mandibular teeth: Incisors, Canine, Premolars and Molars
3. Mucous membrane and underlying tissues anterior to the first mandibular molar (supplied by Lingual nerve)

Note: To anesthetize the soft tissue posterior to the 1^st molar Long Buccal nerve should be anesthetized.

Indications:

1. For Extraction, Root Canal Treatment, Flap surgery, Implant placement or any other Procedure on Mandibular Teeth.
2. Surgical procedures performed on Soft tissue and Hard tissue anterior to the First Mandibular Molar where Inferior alveolar nerve block along with anesthesia to Lingual nerve should be given.
3. Surgical procedures performed on Soft tissue and Hard tissue posterior to the First Mandibular Molar where Inferior alveolar nerve block along with anesthesia to Long Buccal nerve should be given.
4. In diagnosis of Pulp Vitality, Trigeminal Neuralgia… etc

Needle Pathway during Insertion:

Needle passes through the Mucosa, Thin Plate of Buccinatormuscle, Loose connective tissue and Fat.

Approximating Structures to the Needle when in Position:

These are the structures present adjacent or surrounding the Needle when the needle is in final position where the Local Anesthetic Agent is deposited.

Needle is present Superior to the following structures:

• Inferior Alveolar vessels
• Inferior alveolar nerve
• Inferior of the internal pterygoid muscle
• Mylohyoid vessels
• Mylohyoid Nerve

Needle is present Anterior to the following structures:

• Deep part of Parotid Gland

Needle is present Medial to the following structures:

• Inner Ramus of Mandibile

Needle is present Lateral to the following structures:

• Lingual Nerve
• Internal Pterygoid Muscle
• Sphenomandibular ligament

Injection Technique used for Inferior Alveolar Nerve Block (Patient Left Side):

The Patient is seated comfortably on the Dental chair and the dentist stands on the right side of the patient partially facing the patient. For the Left side IANB the Dentist stands more to the Front of the patient. (These are for a Right Handed Dentist)

The Head of the patient is placed such that his/her Mouth is open and the Body of Mandible is parallel to the floor.

The Dentist / Operator uses his/her left index finger or Thumb to palpate the Mucobuccal fold. If thumb is used teh index finger can be placed on extra orally behind the ramus thus holding the mandible between your thumb and index finger to assess the width of the Ramus.

The finger is then moved posterior to contact the External oblique ridge on the anterior border of the Ramus of mandible.

From here it is moved up or Down in search of the greatest depression called the Coronoid Notch which is in direct line with the Mandibular sulcus.

The palpating finger is moved lingually across the retromolar triangle and onto the internal oblique ridge.

The finger which is on the coronoid notch and in contact with the internal oblique ridge is moved to the buccal side to move the Buccal Sucking pad away the path of insertion.

This gives better exposure to the internal oblique ridge, the pterygomandibular raphae and the pterygomandibular depression.

The patient is asked to keep his/her mouth wide open.

The Needle is inserted parallel to the occlusal plane of the mandibular teeth from the opposite side (Approximately over opposite side Premolar) of the mouth at a level bisecting the finger or thumbnail penetrating the tissues of the pterygotemporal depression, and entering the pterygomandibular space.

The needle is penetrated until bone is contacted on the internal surface of the ramus of the mandible.

This is the place where the Mandibular sulcus funnels into the Mandibular foramen.

After contacting bone the needle is withdrawn about 1mm and then 1 to 2 ml of solution is deposited slowly over a duration of 2 minutes into the tissue.

Technique for Anesthetizing Lingual Nerve: The needle is withdrawn about half of its length which was inserted and the Local anaesthetic solution is injected in the area which anesthetizes the Lingual Nerve.

• Modifications of Inferior alveolar nerve block

How to determine the depth or length of the needle to be inserted in Inferior alveolar nerve block ?

The Amount of needle to be inserted should be estimating when the needle tip has been advanced half the distance between the Thumb and index finger (Or half the width of Ramus)

Symptoms of Anesthesia in Inferior Alveolar Nerve Block:

1. Subjective Symptoms: Tingling sensation and Numbness of the lower lip and the tip of the tongue when Lingual Nerve is anesthetized.
2. Objective Symptoms: Instrumentation should be done, use either the Tip of a blunt Probe or Elevator to check for Objective symptoms. The anesthetized tissue and teeth should be pressed and tapped as compared to the normal side without anesthesia.

Complications of Inferior Alveolar Nerve Block:

Muscle Trismus, Hematoma, Needle Breakage, Mucosal irritation and Transient Hemifacial Paralysis is the term used for depicting the Complication of Inferior Alveolar nerve block.

Click on Link to Read more about Transient Hemifacial Paralysis and its Management

Also Check out other nerve block techniques like Infra Orbital Nerve Block Technique and Posterior Superior Alveolar Nerve Block.