Trigeminal nerve



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Dr. Kaan Yücel http://yeditepedentistryanatomy.wordpress.com




23.November.2011 Wednesday

TRIGEMINAL NERVE

The trigeminal nerve (CN V) has two roots: motor and sensory. The largest of all the cranial nerves, the trigeminal nerve gives rise to a small motor root originating in the motor nucleus within the pons and medulla oblongata, and a larger sensory root which finds its origin in the anterior aspect of the pons. CN V is the sensory nerve for the face and the motor nerve for the muscles of mastication and several small muscles. The sensory portion of the trigeminal supplies touch-pain-temperature to the face.

The trigeminal nerve [V] divides into three major divisions-the ophthalmic [V1], maxillary [V2], and mandibular [V3] nerves-before leaving the middle cranial fossa. These nerves are named according to their main areas of termination: the eye, maxilla, and mandible, respectively.

Each of these divisions passes out of the cranial cavity to innervate a part of the face, so most of the skin covering the face is innervated by branches of the trigeminal nerve [V]. The exception is a small area covering the angle and lower border of the ramus of mandible and parts of the ear, which are innervated by the trigeminal [V], facial [VII], vagus [X], and cervical nerves.

The mandibular division carries the motor portion. The motor portion conveys proprioceptive impulses from the temporomandibular joint. The motor division of the nerve supplies the muscles of mastication: masseter, temporal, pterygoid, mylohyoid, and digastric. These muscles produce elevation, depression, protrusion, retraction, and the side-to-side movements of the mandible. The motor division also supplies the tensor tympani and tensor palati muscles.

Trigeminal Ganglion

The sensory root of the trigeminal nerve forms the trigeminal (semilunar or gasserian) ganglion situated within Meckel’s cavity on the anterior surface of the petrous portion of the temporal bone. The trigeminal gangion, which is also termed the semilunar ganglion, is equivalent to the dorsal sensory ganglion of a spinal nerve. It is crescent-shaped and is situiated within an invaginated pocket of dura in the middle cranial fossa. It lies near the apex of the petrous temporal bone. The trigeminal ganglion represents the first cell station for all sensory fibres of the trigeminal nerve except those subserving proprioception. In addition, the trigeminal nerve is associated with four autonomic ganglia, the ciliary, pterygopalatine, otic and submandibular.

The central connections of the trigeminal nerve:

The central process of the trigeminal ganglion cells enter the lateral aspect of the pons and divide into ascending and descending branches which terminate in one or other component of the sensory nucleus of V. This nucleus consists of three parts, each of which appears to subserve different sensory modalities: a chief sensory nucleus in the pontine tegmentum concerned with touch; a descending, or spinal nucleus receiving proprioceptive afferents. The motor root of the trigeminal nerve lies just medial to the sensory nucleus in the upper part of the pons; its efferents pass out with the sensory fibres and are distributed by the way of the mandibular division of the nerve.



OPHTHALMIC NERVE

The ophthalmic nerve (CN V1), the superior division of the trigeminal nerve, is the smallest of the three divisions of CN V. It exits the skull through the superior orbital fissure and enters the orbit.



MAXILLARY NERVE (see appendix for Table 1)

The maxillary nerve (CN V2), the intermediate division of the trigeminal nerve, arises as a wholly sensory nerve. CN V2 supplies upper lip, lateral and posterior portions of nose, upper cheek, anterior temple, mucosa of nose, upper jaw, upper teeth, roof of mouth, and dura of part of the middle cranial fossa.

CN V2 passes anteriorly from the trigeminal ganglion and leaves the cranium through the foramen rotundum in the base of the greater wing of the sphenoid. It enters the pterygopalatine fossa, where it gives off branches to the pterygopalatine ganglion and continues anteriorly, entering the orbit through the inferior orbital fissure.

The middle meningeal nerve is the only branch of the maxillary division within the cranium and provides sensory innervation to the dura mater in the middle cranial fossa.

Within the pterygopalatine fossa, several branches are given off including the pterygopalatine, zygomatic, and posterior superior alveolar nerves. The anterior nasal septum, floor of the nose and premaxilla from canine to canine is innervated by a branch known as the nasopalatine nerve. The nasopalatine nerve courses downward and forward from the roof of the nasal cavity to the floor to enter the incisive canal. It then enters the oral cavity through the incisive foramen to supply the palatal mucosa of the premaxilla.

The hard and soft palate is innervated by the palatine branches; the greater (anterior) and lesser (middle and posterior) palatine nerves. The greater palatine nerve exits the greater palatine foramen onto the hard palate and provides sensory innervation to the palatal mucosa and bone of the hard and soft palate. The lesser palatine nerves emerge from the lesser palatine foramen to innervate the soft palate and tonsillar region.

The pharyngeal branch leaves the pterygopalatine ganglion from its posterior aspect to innervate the nasopharynx.

The zygomatic nerve gives rise to two branches after passing anteriorly from the pterygopalatine fossa to the orbit. The nerve passes through the inferior orbital fissure and divides into the zygomaticofacial and zygomaticotemporal nerves supplying the skin over the malar prominence and skin over the side of the forehead respectively. The zygomatic nerve also communicates with the ophthalmic division via the lacrimal nerve sending fibers to the lacrimal gland.

The posterior superior alveolar (PSA) nerve branches off within the pterygopalatine fossa prior to the maxillary nerve’s entrance into the orbit. The PSA travels downward along the posterior aspect of the maxilla to supply the maxillary molar dentition including the periodontal ligament and pulpal tissues, as well as the adjacent gingiva and alveolar process. The mucous membrane of the maxillary sinus is also innervated by the PSA. It is of clinical significance to note that the PSA does not always innervate the mesiobuccal root of the 1st molar. Several dissection studies have been performed tracing the innervation of the 1st molar back to the parent trunk. In the absence of the middle superior alveolar nerve, the posterior superior alveolar nerve may provide innervation to the premolar region. The PSA was found to innervate the premolar region in 26% of dissections where the MSA was not present

Within the infraorbital canal, the maxillary division is known as the infraorbital nerve and gives off the middle and anterior superior alveolar nerves. When present, the middle superior alveolar (MSA) nerve descends along the lateral wall of the maxillary sinus to innervate the 1st and 2nd premolar teeth. It provides sensation to the periodontal ligament, pulpal tissues, gingiva and alveolar process of the premolar region as well as the mesiobuccal root of the 1st molar in some cases.. In its absence, the premolar region derives it’s innervation from the PSA and ASA nerves.

The anterior superior alveolar (ASA) nerve descends within the anterior wall of the maxillary sinus. A small terminal branch of the ASA communicates with the MSA to supply a small area of the lateral wall and floor of the nose. It also provides sensory innervation to the periodontal ligament, pulpal tissue, gingiva and alveolar process of the central and lateral incisor and canine teeth. In the absence of the MSA, the ASA has been shown to provide innervation to the premolar teeth.

The three superior alveolar nerves anastomose to form a network known as the dental plexus which is comprised of terminal branches coming off the larger nerve trunks. These terminal branches are known as the dental, interdental, and interradicular nerves. The dental nerves innervate each root of each individual tooth in the maxilla by entering the root through the apical foramen and supplying sensation to the pulp. Interdental and interradicular branches provide sensation to the periodontal ligaments, interdental papillae and buccal gingiva of adjacent teeth.



MANDIBULAR NERVE (see appendix for Table 2)

The mandibular nerve (CN V3) is the inferior and largest division of the trigeminal nerve. The mandibular nerve [V3] exits the skull through the foramen ovale. CNV3 supplies lower lip, chin, posterior cheek, temple, external ear, mucosa of lower part of mouth, anterior two-thirds of the tongue, and portions of the dura of anterior and middle cranial fossae. It is formed by the union of sensory fibers from the sensory ganglion and the motor root of CN V in the foramen ovale in the greater wing of the sphenoid, through which CN V3 emerges from the cranium. CN V3 has three sensory branches that supply the area of skin derived from the embryonic mandibular prominence. It also supplies motor fibers to the muscles of mastication. CN V3 is the only division of CN V that carries motor fibers. The major cutaneous branches of CN V3 are the auriculotemporal, buccal, and mental nerves.

The sensory root of the mandibular nerve arises from the trigeminal ganglion, whereas the motor root arises from the motor nucleus of the pons and medulla oblongata. The sensory root passes through the foramen ovale almost immediately after coming off the trigeminal ganglion. The motor root passes underneath the ganglion and through the foramen ovale to unite with the sensory root just outside the cranium forming the main trunk of the mandibular nerve. The nerve then divides into anterior and posterior divisions. The mandibular nerve gives off branches from its main trunk as well as the anterior and posterior divisions.

The main trunk gives off two branches known as the nervus spinosus (meningeal branch) and the nerve to the medial pterygoid. The nervus spinosus supplies the meninges of the middle cranial fossa as well as the mastoid air cells. The nerve to the medial pterygoid is a small motor branch that supplies the medial (internal) pterygoid muscle.

Three motor and one sensory branch are given off by the anterior division of the mandibular nerve. The masseteric, deep temporal, and lateral pterygoid nerves supply the masseter, temporalis and lateral (external) pterygoid muscles respectively. The sensory division known as the buccal (buccinator or long buccal) nerve, runs forward between the two heads of the lateral pterygoid muscle, along the inferior aspect of the temporalis muscle, to the anterior border of the masseter muscle. Here it passes anterolaterally to enter the buccinator muscle however it does not innervate this muscle. The buccinator muscle is innervated by the buccal branch of the facial nerve. The buccal nerve provides sensory innervation to the skin of the cheek, buccal mucosa and buccal gingiva in the mandibular molar region.

The posterior division of the mandibular branch gives off two sensory branches (the auriculotemporal and lingual nerves) and one branch made up of both sensory and motor fibers (the inferior alveolar nerve).

The auriculotemporal nerve ascends from the upper border of the parotid gland between the superficial temporal vessels and the auricle. It supplies the skin of the auricle, the external auditory meatus, the outer surface of the tympanic membrane, and the skin of the scalp above the auricle.

The lingual nerve provides sensory innervation to the anterior two thirds of the tongue, mucosa of the floor of the mouth, and lingual gingiva.

The inferior alveolar branch of the mandibular nerve descends in the region between the lateral aspect of the sphenomandibular ligament and the medial aspect of the ramus of the mandible. It travels along with, but lateral and posterior to, the lingual nerve. While the lingual nerve continues to descend within the pterygomandibular space, the inferior alveolar nerve enters the mandibular canal through the mandibular foramen. Just before entering the mandibular canal the inferior alveolar nerve gives off a motor branch known as the mylohyoid nerve. The nerve travels along with the inferior alveolar artery and vein within the mandibular canal and divides into the mental and incisive nerve branches at the mental foramen. The inferior alveolar nerve provides sensation to the mandibular posterior teeth.

The incisive nerve is a branch of the inferior alveolar nerve which continues within the mandibular canal to provide sensory innervation to the mandibular anterior teeth.

The mental nerve emerges from the mental foramen to provide sensory innervation to the mucosa in the premolar/canine region as well as the skin of the chin and lower lip.

The mylohyoid nerve supplies the mylohyoid muscle as well as the anterior belly of the digastric.



THE ANATOMY OF THE TRIGEMINAL NERVE ANESTHESIA

(see appendix Table 3)
The local infiltration technique anesthetizes the terminal nerve endings of the dental plexus. It is indicated when an individual tooth or a specific, isolated area requires anesthesia. The procedure is performed in the direct vicinity of the site of infiltration.

The field block anesthetizes the terminal nerve branches in the area of treatment. Treatment can then be performed in an area slightly distal to the site of injection. The deposition of local anesthetic at the apex of a tooth for the purposes of achieving pulpal and soft tissue anesthesia is often employed by many dental and maxillofacial professionals.

A nerve block anesthetizes the main branch of a specific nerve allowing treatment to be performed in the region innervated by the nerve.

The most commonly anesthetized nerves in dentistry are branches or nerve trunks associated with the maxillary and mandibular divisions of the trigeminal nerve. Current studies afford a more detailed knowledge of the branching of various divisions of the trigeminal nerve, the great sensory nerve of the head region.

Anesthesia of the teeth and soft and hard tissues of the oral cavity cannot be achieved without knowledge of the trigeminal nerve (fifth cranial nerve) and its branches. Regional, field, and local anesthesia of the maxilla and mandible depend upon the deposition of anesthetic solution near terminal nerve branches or a main nerve trunk of the trigeminal nerve.

Achieving excellence in pain control is an intrinsic, yet challenging, goal of dentistry. Dentists are aware of the relative ease of successfully performing pain-free intraoperative procedures in maxillary teeth. The maxilla’s relatively porous alveolar bone allows for the use of straightforward local anesthetic techniques of paraperiosteal field blocks or infiltrations. The mandible is different. The outer layer of cortical bone is thick and nonporous and thus normally requires the use of a nerve block at a site away from the teeth being treated.



ANESTHESIA OF THE MAXILLARY TEETH

From an anatomical perspective, maxillary injections generally are believed to be not only more predictable than mandibular injections, but also more benign and associated with fewer complications. However, this is not necessarily true, particularly for block injections. For example, the posterior superior

alveolar, or PSA, or tuberosity block, infraorbital block and the second division block carry the needle into the depths of the midface and approximate to the base of the skull, the orbit and associated structures. Complications associated with such maxillary injections (such as arterial bleeding and temporary blindness [amaurosia]) can result in considerable difficulty and discomfort for the patient.

Maxillary nerve block (V2 block) can be used to anesthetize maxillary teeth, alveolus, hard and soft tissue on the palate, gingiva, and skin of the lower eyelid, lateral aspect of nose, cheek, and upper lip skin and mucosa on side blocked.



Techniques of Maxillary Regional Anesthesia

The techniques most commonly employed in maxillary anesthesia include supraperiosteal (local) infiltration, periodontal ligament (intraligamentary) injection, posterior superior alveolar nerve block, middle superior alveolar nerve block, anterior superior alveolar nerve block, greater palatine nerve block, nasopalatine nerve block, local infiltration of the palate, and intrapulpal injection. Of less clinical application are the maxillary nerve block and intraseptal injection.



Supraperiosteal (Local) Infiltration

The supraperiosteal or local infiltration is the one of the simplest and most commonly employed techniques for achieving anesthesia of the maxillary dentition. This technique is indicated when any individual tooth or soft tissue in a localized area is to be treated. a useful adjunct to the supraperiosteal injection or a nerve block. Indications for the use of this technique are the need to anesthetize an individual tooth or teeth, need for soft tissue anesthesia in the immediate vicinity of a tooth, and partial anesthesia following a field block or nerve block.


Periodontal Ligament (Intraligamentary Injection)


The periodontal ligament or intraligamentary injection is is a useful adjunct to the supraperiosteal injection or a nerve block. Often, it is used to supplement these techniques to achieve profound anesthesia of the area to be treated. Indications for the use of this technique are the need to anesthetize an individual tooth or teeth, need for soft tissue anesthesia in the immediate vicinity of a tooth, and partial anesthesia following a field block or nerve block. The sulcus between the gingiva and the tooth is the injection site for the periodontal ligament injection.

POSTERIOR SUPERIOR ALVEOLAR (PSA) NERVE BLOCK

The posterior superior alveolar (PSA) nerve block is otherwise known as the tuberosity block or the zygomatic block. The PSA nerve block is used to anesthetize the pulpal tissue, corresponding alveolar bone, and buccal gingival tissue to the maxillary 1st, 2nd, and 3rd molars. The area of insertion is the height of mucobuccal fold between1st and 2nd nd molar. With this block injection, the dentist directs the needle high onto the tuberosity of the maxilla to approach the PSA nerve before it enters the bony maxilla.

Occasionally, the PSA block will not result in complete maxillary molar anesthesia. This may occur because of displaced branches of the PSA nerves entering the palatal root of the molars, the lingual aspect of the premolars, or both. In these instances, the dentist must remember that the greater palatine injection may add to the efficiency of a PSA injection.

MIDDLE SUPERIOR ALVEOLAR (MSA) NERVE BLOCK

The middle superior alveolar (MSA) nerve block is useful for procedures where the maxillary premolar teeth or the mesiobuccal root of the 1st molar require anesthesia. Although not always present, it is useful if the posterior or anterior superior alveolar nerve blocks or supraperiosteal infiltration fails to achieve adequate anesthesia. The MSA nerve block is used to anesthetize the maxillary premolars, corresponding alveolus, and buccal gingival tissue. It is present in about 28% of the population.

The dentist identifies the height of the mucobuccal fold above the maxillary 2nd premolar. This will be the injection site.

Traditionally, researchers and clinicians have understood that there are three nerves (the anterior superior alveolar, or ASA, middle superior alveolar, or MSA, and the PSA) that carry sensation to the maxillary teeth. It is interesting that many patients have only two maxillary alveolar nerves; the MSA nerve, the innervation ascribed to the premolar teeth, often is missing. In these instances, the PSA nerve innervates the premolar/ canine region, and infiltration anesthesia in the region of the molars induces primary anesthesia for the premolars. There are no anatomical predictors of the pattern of innervation for an individual. When attempting to anesthetize the maxillary premolars, the dentist should understand that infiltration in the vicinity of the apexes of these teeth will induce anesthesia regardless of the origin of the dental nerves.

In addition, the clinician may have to modify his or her approach to infiltrating in the premolar area because of an occasional anatomical feature. In some patients, an extensive bony prominence, the zygomaticoalveolar crest, can approximate the apexes of the premolar teeth, which prevents the needle’s approach to this vicinity. Because most, if not all, of the MSA fibers are incorporated into the PSA nerve, molar infiltration or a PSA nerve block would be the alternative choice in these cases.

ANTERIOR SUPERIOR ALVEOLAR (ASA) NERVE BLOCK

The ASA nerve block is used to anesthetize the maxillary canine, lateral incisor, central incisor, alveolus, and buccal gingiva. The area of insertion is height of mucobuccal fold in area of lateral incisor and canine. In order to anesthetically block the anterior and middle superior alveolar nerves, it is essential to localize the infraorbital foramen which, when reached with a needle, permits the diffusion of the anesthetic solution through the infraorbital canal.

Some dentists consider the infraorbital or ASA nerve block to be a complicated injection fraught with risks and to be avoided. Accordingly, dentists do not use the ASA nerve block with the same frequency as they do the PSA block. This might seem to be primarily because of the dentist’s lack of understanding ofthe anatomy involved, as well as a misconception regarding the dangers to the eye. Actually, the ASA nerve block can be extremely safe as well as highly successful when one adheres to a particular protocol based on a sound knowledge of the anatomy, specifically an awareness of the relative location of the infraorbital foramen.

Infraorbital block anesthetizes the anterior and middle maxillary alveolar nerves, inferior palpebral, lateral nasal and superior labial with insensibility of the maxillary incisors, canines and pre-molars, including their vestibular osseous support and the soft tissues which cover them, as well as the mesiovestibular root of the maxillary first molar, part of the maxillary sinus, nose, superior labial and inferior palpebral.

The anatomical location of this foramen has been studied by numerous authors. Martani and Stefani (1965), studying the position of this anatomic accident within statistical, morphological and topographical aspects, provide an extensive bibliographical review of this topic.

In adults, the infraorbital foramen lies significantly below the infraorbital rim (8 to 10 millimeters), a safe distance from the cavity of the orbit. To locate the infraorbital foramen, the dentist can palpate a small depression in the infraorbital rim—the infraorbital notch—created by the zygomaticomaxillary suture. The clinician places his or her finger in this notch, and directs the needle through the vestibular mucosa over the first premolar tooth and toward the finger. The tip of the needle stays approximately 10 mm below the infraorbital rim. The needle actually penetrates the soft tissue to a minimum depth of approximately 10 to 12 mm because of the height of the maxillary vestibule and the relative position of the foramen. The needle should stay adjacent to the periosteum to avoid engaging the overlying soft tissues of the face, where the facial artery could be encountered, creating significant bleeding. In addition, the clinician should be aware that with this injection, he or she may anesthetize peripheral branches of the facial nerve (VII) and render the patient with a partial facial paralysis. The dentist should advise the patient that this paralysis is transient and is of no lasting consequence.



The superior lateral labial frenum as the new anatomical reference to be observed for the locafization of the needle insertion point in infraorbital intrabuccal blockage. The superior lateral labial frenum is a fold in the mucosa of the gingival sulcus, inserting in the region of the maxillary canines and pre-molars.

In children and adolescents, the vertical growth of the facial skeleton is incomplete, and the infraorbital foramen is closer to the infraorbital rim than it is in adults. For this reason, the dentist should exercise more caution when administering an infraorbital block in the younger patient.



PALATAL INNERVATION

The mucosa of the hard palate and the palatal gingiva are supplied by the nasopalatine and greater palatine nerves. The boundary between the areas innervated by the two nerves corresponds roughly to a line drawn between the maxillary canines; however, the two areas are not so sharply delineated as such an

imaginary line might suggest. The greater palatine nerve may play a larger role in the innervation of the anterior palate than had previously been thought.

NASOPALATINE NERVE BLOCK

The nasopalatine nerve block can be used to anesthetize the soft and hard tissue of the maxillary anterior palate from canine to canine. The area of insertion is incisive papilla into incisive foramen.

Fibers of the superior alveolar plexus occasionally join the nasopalatine nerve just below the nasal floor and travel with the nasopalatine nerve to reach the central incisor on the side of the mouth being innervated. It may be necessary to anesthetize the nasopalatine nerve to completely anesthetize the central incisors. This is best accomplished by injecting immediately lateral to the incisive papilla.

GREATER PALATINE NERVE BLOCK

The greater palatine nerve block is useful when treatment is necessary on the palatal aspect of the maxillary premolar and molar dentition. This technique targets the area just anterior to the greater palatine canal. In the greater palatine canal technique, the area of insertion is greater palatine canal. The target area is the maxillary nerve in the pterygopalatine fossa. The greater palatine nerve exits the canal and travels forward between the bone and soft tissue of the palate. The dentist performs a greater palatine block and waits 3 3-5 mins. Then h/she inserts needle in previous area and walks into greater palatine foramen.

Most anatomy textbooks place the greater palatine foramen, which is accessed to administer a greater palatine nerve block or a second division nerve block, palatally opposite the second molar. More recent studies, however, localize the greater palatine foramen farther posteriorly than is traditionally depicted.

The foramen has been shown to lie 1.9 mm in front of the posterior border of the hard palate and 15 mm from the palatal midline. These measurements are useful for more easily locating the greater palatine foramen and enhancing the anesthetic injection technique in the posterior palate.

The greater palatine foramen can be located by on the palatal tissue approximately one centimeter medial to the junction of the 2nd and 3rd molar. While this is the usual position for the foramen, it may be located slightly anterior or posterior to this location.

ANESTHESIA OF THE MANDIBULAR TEETH

The buccal cortical plate of the mandible most often is sufficiently dense to preclude effective infiltration anesthesia in its vicinity. The infiltration techniques do not work in the adult

mandible due to the dense cortical bone. Therefore, the dentist must rely on block anesthesia for effectively anesthetizing mandibular teeth. Nerve blocks are utilized to anesthetize the inferior alveolar, lingual, and buccal nerves. It provides anesthesia to the pulpal, alveolar, lingual and buccal gingival tissue, and skin of lower lip and medial aspect of chin on side injected.

It is interesting to note that various descriptions of the socalled usual innervation of mandibular teeth are generalized and incomplete. They do not accurately reflect the anatomical variability of various sensory nerves to the mandible. This could be one reason why the rate of failure in achieving adequate pulpal anesthesia via the inferior alveolar nerve block injection has been so high.



INFERIOR ALVEOLAR NERVE BLOCK

The most common approach to inferior alveolar anesthesia is the traditional Halstead method. The area of insertion is the mucous membrane on the medial border of the mandibular ramus at the intersection of a horizontal line (height of injection) and vertical line (anteroposterior plane). As the target site for the deposition of anesthetic solution in the conventional inferior alveolar block injection, the mandibular foramen is an essential structure to accurately locate. The target for this technique is the mandibular nerve as it travels on the medial aspect of the ramus, prior to its entry into the mandibular foramen. The lingual, mental, and incisive nerves are also anesthetized.

It was found that the position of the foramen was indeed variable, and it was usually found anterior to the midpoint of the ramus of the mandible when the anterior border of the mandible is defined as the internal oblique ridge (that is, temporal crest). It was also described that the foramen was slightly above the level of the molars; however, others could not confirm this. It was also found that the foramen was located below the occlusal surface of the molars in many cases. It was,therefore, concluded that clinicians should be aware of the variability in the location of the mandibular foramen when seeking to anesthetize the inferior alveolar nerve. In particular, it was suggested that dentists consider use of panoramic radiographs in locating the mandibular foramen rather than relying on bony landmarks.

With the mouth open maximally, identify the coronoid notch and the pterygomandibular raphae. Three quarters of the anteroposterior distance between these two landmarks, and approximately six to ten millimeters above the occlusal plane is the injection site.

During administration of anesthetic to the inferior alveolar nerve, the clinician must be aware of the proximal extremity of the maxillary artery, as well as the course of the inferior alveolar artery. Fortunately, at the level of the mandibular foramen, the position of the inferior alveolar artery is such that it is protected from the dental needle.

Traditionally, the inferior alveolar nerve block (IANB), also known as the “standard mandibular nerve block” or the “Halsted block,” has been used to provide anesthesia in mandibular teeth. This technique, however, has a success rate of only 80 to 85 percent, with reports of even lower rates. Investigators have described other techniques as alternatives to the traditional approach, of which the Gow-Gates mandibular nerve blockand Akinosi-Vazirani closed-mouth mandibular nerve block techniques have proven to be reliable. Dentists who know how to perform all three techniques increase their probability of providing successful mandibular anesthesia in any patient.

Dentists who are skilled at using the Gow-Gates and Akinosi- Vazirani techniques will have a higher likelihood of successfully providing anesthesia in patients who have anatomy that differs from what is expected. Similarly, these two techniques have a higher likelihood of bathing an accessory branch of the inferior alveolar nerve with local anesthetic, because they result in the drug’s being administered at a site deeper than that accomplished through the traditional IANB.

The primary goal of each of the three mandibular nerve blocks is anesthesia of the inferior alveolar nerve, which innervates the pulps of the mandibular teeth on the same side of the mouth, as well as the buccal periodontium anterior to the mental foramen. For each of the three techniques, this goal is accomplished by depositing anesthetic within the pterygomandibular space. This anatomical space contains the inferior alveolar nerve, as well as the lingual nerve, which usually also is anesthetized by means of these techniques. The pterygomandibular space also contains the inferior alveolar artery and vein and the sphenomandibular ligament. This space is bordered laterally by the ramus of the mandible, medially and inferiorly by the medial pterygoid muscle, superiorly by the lateral pterygoid muscle, posteriorly by the parotid gland and anteriorly by the thin buccinator muscle.

Any of these techniques may be used, and they can be the first choice when performing dental work in the mandibular arch. The Gow-Gates and Akinosi-Vazirani methods are indicated particularly when there is anatomical variation or accessory innervation. The Akinosi- Vazirani method also is indicated when the patient has trouble opening his or her mouth or whose tongue persistently obstructs the view of the soft-tissue landmarks used in the IANB.

GOW-GATES MANDIBULAR NERVE BLOCK

Gow-Gates initially described what became known as the “Gow-Gates mandibular nerve block” in 1973. The objective of the technique is to place the needle tip and administer the local anesthetic at the neck of the condyle. This position is in proximity to the mandibular branch of the trigeminal nerve after it exits the foramen ovale.



AKINOSI-VAZIRANI CLOSED-MOUTH MANDIBULAR NERVE BLOCK

Two dentists independently described the closed mouth mandibular nerve block as an alternative to the IANB. In 1977, Akinosi brought this method to the attention of educators, but they soon realized that this technique had been published by Vazirani in 1960. What makes this technique unique is that the patient’s mouth is closed. The objective is to place the needle tip between the ramus and the medial pterygoid muscle.



LINGUAL NERVE BLOCK

Branches of the lingual nerve supply the lingual gingiva and adjacent mucosa of the mandible. The lingual nerve courses through the infratemporal fossa anterior to the inferior alveolar nerve. This nerve typically is anesthetized with a bolus of anesthetic solution injected during withdrawal of the needle after an inferior alveolar nerve block. Although the lingual nerve is frequently anesthetized during the inferior alveolar nerve block, the bolus delivery ensures lingual nerve anesthesia. The lingual nerve passes from the infratemporal fossa into the floor of the mouth close to the alveolus just distolingual to the third molar. Along its course, adjacent to the alveolar process in the vicinity of the second and third molars, the lingual nerve is quite vulnerable to trauma.



BUCCAL NERVE BLOCK

Traditionally, the buccal nerve block injection is delivered to the anterior ramus of the mandible at the level of the mandibular molar occlusal plane in the vicinity of the retromolar fossa. The dentist should identify the most distal molar tooth on the side to be treated. The tissue just distal and buccal to the last molar tooth is the target area for injection



MENTAL NERVE BLOCK

Mental and incisive nerves are the terminal branches for the inferior alveolar nerve. It provides sensory input for the lower lip skin, mucous membrane, pulpal/alveolar tissue for the premolars, canine, and incisors on side blocked. The area of injection mucobuccal fold at or anterior to the mental foramen. This lies between the mandibular premolars. The mental nerve is the terminal branch of the inferior alveolar nerve and exits the mandible via the mental foramen. The position of this foramen varies greatly, making it difficult to predictably locate this nerve using intraoral landmarks in a patient with an intact dentition. This task is even more daunting in a patient with a mutilated dentition or in the edentulous patient. In spite of the limitations inherent with the variable foramen locations, the success rate of a mental block injection approaches 100 percent, possibly because of the wider diffusion of the anesthetic solution in the soft tissues.



LEGAL COMPLAINTS

Most local anaesthesia 'failures' occur with IAN blocks. Injuries to inferior alveolar and lingual nerves are caused by local analgesia block injections and have an estimated injury incidence of between 1:26,762 to 1/800,000. The nerve that is usually damaged during inferior alveolar nerve block injections is the lingual nerve. which accounts for 70% of nerve injuries. Persisting anesthesia or paresthesia due to damage to various branches of the trigeminal nerve is a common complication in dental surgical procedures, especially associated with lower third molar removal. Cases relating to sensory loss of lingual nerve and inferior alveolar nerve following inferior dental block injections for restorative procedures have occasionally been presented as a legal complaint.


References

  • Bahl R. Local anesthesia in dentistry. Anesth Prog. 2004;51(4):138-42.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2007495/pdf/anesthprog00004-0030.pdf

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http://blogohj.oralhealthjournal.com/2011/06/trigeminal-nerve-injuries-related-to-local-anaesthesia-in-dentistry.html

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APPENDIX
Table 1.

Branches of the Maxillary Division

  1. Middle Meningeal

  2. Pterygopalatine Nerves
    • Sensory fibers to the orbit
    • Nasal Branches
    • Nasopalatine Nerve
    Greater Palatine Nerve
    • Lesser Palatine Nerve
    • Pharyngeal Branch

  3. Zygomatic
    • Zygomaticofacial
    • Zygomaticotemporal

  4. Posterior Superior Alveolar Nerve Block

  5. Infraorbital
    • Middle Superior Alveolar
    • Anterior Superior Alveolar
    • Inferior Palpebral
    • Lateral Nasal
    • Superior Labial

Table 2.


Branches of the Mandibular Division

  1. Main Trunk
    Nervous Spinosus
    Nerve to the Medial Pterygoid

  2. Anterior Division
    Masseteric
    Deep Temporal
    Lateral Pterygoid
    Buccal Nerve

  3. Posterior Division
    Auriculotemporal
    Lingual
    Inferior Alveolar
    Nerve to the Mylohyoid

Table 3.


Nerve to block

Technique / Area of insertion

Posterior Superior Alveolar

The height of the mucobuccal fold over the maxilalry 2nd molar

Middle Superior Alveolar

The height of the mucobuccal fold above the maxillary 2nd premolar

Anterior Superior Alveolar

The height of the mucobuccal fold above the maxillary 1st premolar

Nasopalatine

The area immediately lateral to the incisive papilla into incisive foramen

Greater Palatine

1 cm. medial to the junction of the 2nd and 3rd molar

Inferior Alveolar

With the mouth open maximally, identify the coronoid notch and the pterygomandibular raphae. Three quarters of the anteroposterior distance between these two landmarks, and approximately six to ten millimeters above the occlusal plane is the injection site.

Buccal

The dentist should identify the most distal molar tooth on the side to be treated. The tissue just distal and buccal to the last molar tooth is the target area for injection.

Mental

The mucobuccal fold at or anterior to the mental foramen which lies between the mandibular premolars

Nerves in italics are the branches of the mandibular nerve.



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