Mandibular Nerve Block

 

Background

Mandibular nerve block involves blockage of the auriculotemporal, inferior alveolar, buccal, mental, incisive, mylohyoid, and lingual nerves. It results in anesthesia of the following areas:

  • Ipsilateral mandibular teeth up to the midline

  • Buccal and lingual hard and soft tissue on the side of the block

  • Anterior two-thirds of the tongue

  • Floor of the mouth

  • Skin over the jaw, the posterior part of the cheek, and the temporal area

Mandibular nerve block is a safe procedure. The process of obtaining informed consent should include discussion of the risk of temporary numbness and paresthesia in the involved region.

Indications

The mandibular nerve area is generally blocked by using more specific nerve blocks rather than by performing a complete nerve block. Indications for complete nerve block include the following:

  • Patients in whom the inferior alveolar nerve (IAN) block fails or is not feasible – Sometimes the teeth may be innervated by an accessory nerve that arises proximal to the IAN and thus may be spared by an IAN block

  • Patients undergoing surgical procedures of the mandible – Mandibular nerve block may be done either as an isolated nerve block or as a complement to general anesthesia; this is applicable to several dental procedures on the lower teeth and surrounding soft tissues

The mandibular nerve block has a success rate of 95%-98%, whereas the IAN block is successful in only 65%-85% of cases.

Contraindications

Contraindications for mandibular nerve block include the following:

  • Acute inflammation at the site of injection

  • Trismatic patients, uncooperative patients, and children (these are specific to the Gow-Gates block [see Technique])

  • Acute infection in the pterygomandibular space, fracture of the mandible, presence of a tumor, or distortion of the regional anatomy (these are specific to the Vazirani-Akinosi block [see Technique])

  • Patients with known allergies to local anesthetic

Technical Considerations

The mandibular nerve is the largest division of the trigeminal nerve, with sensory roots from the trigeminal ganglion and motor roots from the pons and the medulla. The 2 roots exit the cranium via the foramen ovale and unite just outside the cranium to form the mandibular nerve. After giving off 2 branches, the mandibular nerve bifurcates into anterior and posterior divisions (see the image below).

Branches of the mandibular nerve Branches of the mandibular nerve

From the main trunk, the nervus spinosus reenters the cranium via the foramen spinosum to provide sensory innervation to the meninges. The nerve to the medial pterygoid is a motor branch that innervates the medial pterygoid muscle. It divides into 2 branches, which are the nerves to the tensor tympani and the tensor veli palatini.

Motor nerves from the anterior division include the following:

  • Masseteric nerve, which supplies the masseters

  • Temporal nerve, which serves the temporalis

  • Lateral pterygoid nerve, which supplies the lateral pterygoid muscle

Sensory nerves from the anterior division include the buccal nerve, which is sensory to the mucosa of the mouth and gums and the skin on the cheek.

Sensory nerves from the posterior division include the following:

  • Auriculotemporal nerve, which is sensory to the external auditory meatus and the external surface of the tympanic membrane

  • Lingual nerve, which travels inferiorly into the pterygomandibular space between the mandibular ramus laterally and the medial pterygoid muscle medially; this nerve provides general sensation to the anterior two-thirds of the tongue, the floor of the mouth, and the lingual gingiva

The IAN descends into the pterygomandibular space along with the lingual nerve. Its sensory branch enters the mandibular canal and is sensory to the lower teeth and gums. It then exits via the mental foramen as the mental and incisive nerves, which are sensory to the chin and the lower teeth. The motor branch to the mylohyoid is given off before the nerve enters the mandibular canal and serves as motor supply to the mylohyoid muscle.


Mandibular Nerve Block Periprocedural Care


Equipment

Equipment used for mandibular nerve block includes the following:

  • 25-gauge long needle (36 mm)

  • Sterile syringe (either aspirating or nonaspirating)

  • Cotton-tip applicators for controlling bleeding

  • Mouth retractors

  • Local anesthetic solutions – Lidocaine 1-2% with or without epinephrine (1:100,000 or 1:200,000 concentration), bupivacaine 0.5%, or mepivacaine 2-3%

Generally, a dose of 1-5 mL is adequate for small dental procedures. If larger volumes are used, care must be taken not to exceed the maximum allowable dose. Reduction of the dose is required in pediatric and older populations, as well as in patients with cardiac, renal, or liver diseases.

Standard monitoring modalities (eg, pulse oximetry, noninvasive blood pressure [NIBP] monitoring, and electrocardiography [ECG]) should be available. Basic resuscitative drugs and equipment should be on hand.


Mandibular Nerve Block Technique



Approach Considerations

The following 3 techniques are used to perform a mandibular nerve block [12:

  • Gow-Gates technique

  • Vazirani-Akinosi technique

  • Coronoid approach

For a clear understanding of the technical descriptions that follow (see below), it is important to be conversant with some dental anatomic terminology. These terms may be illustrated by considering the anatomy of the second maxillary molar tooth.

The second maxillary molar tooth is placed between the first and third molar teeth and is the seventh tooth from the midline. The visible part of the tooth is called the crown, and the parts covered by the gum are the 3 roots of the tooth. The dividing line that separates the roots from the crown is called the cervical line.

The crown has the following 5 surfaces:

  • Occlusal

  • Buccal

  • Lingual (palatal)

  • Mesial

  • Distal

The occlusal, buccal, and lingual surfaces are self-explanatory, referring to those particular surfaces of the tooth. The mesial surface is the anterior surface of the tooth—in this case, the surface adjoining the first molar tooth. The distal surface is the posterior surface—in this case, the surface adjoining the third molar tooth.

The buccal surface of the tooth has the following 2 protuberances or cusps, which are separated by the buccal groove:

  • An anterior protuberance, called the mesiobuccal cusp

  • A posterior protuberance, called the distobuccal cusp

Similarly, the lingual surface has a mesiolingual cusp and a distolingual cusp, which are separated by the lingual groove.

Techniques for Mandibular Nerve Block

Gow-Gates technique

This technique is mainly indicated in patients undergoing dental procedures in whom inferior alveolar nerve block does not provide adequate analgesia owing either to anatomical variation or due to accessory nerve supply. This approach provides true mandibular nerve block as it blocks the trunk of the nerve before it divides into its three main terminal branches. The incidence of intravascular injection is also lesser with this approach.

A disadvantage of this approach is that there is undesired anesthesia of the lower lip and temporal region. The onset time of the block is also prolonged. 

The patient is placed in a semisupine position or on a dental chair with the operator standing on the same side as the block to be performed. [345The mouth is opened as wide as possible. This is essential for the success of this block. Anatomic landmarks include the following:

  • Corner of the mouth

  • The intertragic notch

  • Distolingual cusp of the second maxillary molar tooth

The aim is to reach the neck of the mandibular condyle.

The second maxillary molar tooth is identified, and a needle is inserted at the level of the mesiolingual cusp along the medial side of the mandibular ramus (see the image below). The point of insertion is much higher than that for an inferior alveolar nerve (IAN) block. The needle is inserted in such a way that it lies parallel to an imaginary line drawn from the intertragic notch to the angle of the mouth.

The Gow-Gates approach for mandibular nerve block The Gow-Gates approach for mandibular nerve block

The needle is advanced by 2.5 cm so as to contact the bony neck of the mandibular condyle. It is then slightly withdrawn, and negative aspiration is confirmed in 2 planes. Finally, 1.8 mL of local anesthetic is injected slowly over 1 minute. This blocks the IAN and its branches and the lingual, mylohyoid, auriculotemporal, and buccal nerves.

Vazirani-Akinosi (closed-mouth) technique

The Vazirani-Akinosi technique has several advantages over the Gow-Gates technique. [67It is useful in trismatic patients and those with ankylotic temporomandibular joint; in addition, it is less traumatic and has a lower complication rate. However, the Vazirani-Akinosi technique is less effective than the Gow-Gates technique. Recent studies have not shown any difference in the quality of pain relief with either of the approaches. [8 This approach is contraindicated if the patient has an infection or inflammation involving the pterygomandibular region or maxillary tuberosity. The main advantages with this approach include a faster onset of action, lesser post-procedure complications, and lesser pain during injection.

The patient is placed in a semisupine position or on a dental chair with the mouth closed. The operator stands on the same side as the block to be performed. Anatomic landmarks include the following:

  • Gingival margin over the second and third maxillary molars

  • Pterygomandibular raphe

The aim is to enter the pterygomandibular space where the IAN, lingual nerve, and mylohyoid nerve are present. This space is bordered laterally by the ramus of mandible, medially and inferiorly by the medial pterygoid muscle, posteriorly by the parotid gland, and anteriorly by buccinators muscle.

The cheek is retracted with a retractor, and the patient is asked to occlude his or her teeth gently. The needle is inserted over the medial aspect of the mandibular ramus, parallel to the occlusal plane at the height of the mucogingival junction of the second and third molars (see the image below). The needle is bent slightly to decrease the chance of entering the muscle belly.

Vazirani-Askinosi technique (a.) point of insertioVazirani-Askinosi technique (a.) point of insertion is medial to the mandibular ramus. (b) the needle is inserted till the hub of the needle is distal to the second upper molar.

The needle is then advanced through the mucous membrane and buccinator muscle to enter the pterygomandibular space. The needle is advanced until the hub is level with the distal surface of the second molar. After negative aspiration, 1.8 mL of local anesthetic is injected slowly over 1 minute.

Coronoid approach

The patient is placed in a supine position with the mouth in a neutral position. The coronoid notch on the side of the block is identified by opening and closing the mouth a few times.

After skin preparation, a 22-gauge needle is inserted at the middle of the notch and advanced to a depth of about 1-2 inches in a plane perpendicular to the base of the skull until the lateral pterygoid plate is reached. The tip of the needle is then withdrawn slightly and redirected posteriorly and inferiorly so that it goes beyond the lateral pterygoid plate. After redirection of the needle, paresthesias in the mandibular region are elicited at a depth of about 1 cm. After aspiration, 3-5 mL of local anesthetic solution is slowly injected.

Complications

If a large volume of the local anesthetic is administered or an inadvertent intravascular injection has taken place, the patient may manifest a systemic toxic response to the local anesthetic used. This may involve minimal to moderate symptoms (eg, anxiety, numbness, dizziness, weakness, and tremors), but in some cases, it can result in central nervous system (CNS) and cardiovascular collapse.

An allergic reaction may develop to the preservatives added to the local anesthetic (eg, methylparaben or sodium metabisulfite) or to an ester-group local anesthetic.

Persistent paresthesia and numbness may be due to trauma to the nerve or local hematoma formation.

Needle-track infection is possible. This can be avoided by employing single-use syringes and needles, using disinfectants, and avoiding areas with active infection.

Hematoma formation is possible. Edema and sloughing of tissues, although rare, can occur.


Mandibular Nerve Block Medication


Medication Summary

The goal of pharmacotherapy is to reduce pain during the procedure.

Local Anesthetics, Amides

Class Summary

Local anesthetics are used for local pain relief.

Lidocaine (Xylocaine with epinephrine)

Lidocaine 1-2% with or without epinephrine (1:100,000 or 1:200,000 concentration) is used. Lidocaine is an amide local anesthetic used in 1-2% concentration. The 1% preparation contains 10 mg of lidocaine for each 1 mL of solution; the 2% preparation contains 20 mg of lidocaine for each 1 mL of solution. Lidocaine inhibits depolarization of type C sensory neurons by blocking sodium channels. Epinephrine prolongs the duration of the anesthetic effects from bupivacaine by causing vasoconstriction of the blood vessels surrounding the nerve axons.

Mepivacaine (Polocaine MPF)

Mepivacaine 2-3% prevents the generation and conduction of nerve impulses.

Bupivacaine and epinephrine (Marcaine with epinephrine, Vivacaine, Sensorcaine with epinephrine)

Bupivacaine 0.5% with or without epinephrine may be used. It decreases permeability to sodium ions in neuronal membranes. This results in the inhibition of depolarization, blocking the transmission of nerve impulses. Epinephrine prolongs the duration of the anesthetic effects from bupivacaine by causing vasoconstriction of the blood vessels surrounding the nerve axons.

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