• Adam T. Hershkin, DMD
• Paul J. Seider, DMD
• Gregory M. Casey, DDS

        INTRODUCTION

Oral surgical and dental procedures are routinely performed in an outpatient setting. Regional anesthesia is the most common method of anesthetizing the patient before office-based procedures. Many techniques can be used to achieve anesthesia of the dentition and surrounding hard and soft tissues of the maxilla and mandible. The type of procedure to be performed as well as the location of the procedure determines the technique of anesthesia to be used. Orofacial anesthetic techniques can be classified into three main categories: local infiltration, field block, and nerve block.

        The local infiltration technique anesthetizes the terminal nerve endings of the dental plexus. This 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 used by many dental and maxillofacial professionals. Although this is commonly termed “local infiltration,” it is important to note that this is a misnomer. Terminal nerve branches are anesthetized in this technique, and it is therefore correctly termed a field block.

        A nerve block anesthetizes the main branch of a specific nerve, allowing treatment to be performed in the region innervated by the nerve.¹ This chapter reviews the essential anatomy of orofacial nerves and details the practical approach to performing nerve blocks and infiltrational anesthesia for a variety of surgical procedures in this region.

Anatomy of the Trigeminal Nerve

General Considerations

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 on the deposition of anesthetic solution near terminal nerve branches or a main nerve trunk of the trigeminal nerve.

        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. The nerve travels forward from the posterior cranial fossa to the petrous portion of the temporal bone within the middle cranial fossa. Here, the sensory root 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 ganglia are paired, one innervating each side of the face. The sensory root of the trigeminal nerve gives rise to the ophthalmic division (V₁), the maxillary division (V₂),and the mandibular division (V₃) from the trigeminal ganglion (Figure 20-1).

        The motor root travels from the brainstem along with but separate from the sensory root. It then leaves the middle cranial fossa through the foramen ovale after passing underneath the trigeminal ganglion in a lateral and inferior direction. The motor root exits the middle cranial fossa along with the third division of the sensory root; the mandibular nerve. It then unties with the mandibular nerve to form a single nerve trunk after exiting the skull. The motor fibers supply the muscles of mastication (masseter, temporalis, medial pterygoid, and lateral pterygoid), mylohyoid, anterior belly of the digastric, tensor veli palatini and tensor tympani muscles.

Figure 20-1. Anatomy of the trigeminal nerve The sensory root of the trigeminal nerve gives rise to the ophthalmic division (V₁), maxillary division (V₂), and the mandibular division (V₃) from the trigeminal ganglion.

Ophthalmic Division

The smallest of the three divisions, the ophthalmic division (V₁) is purely sensory and travels anteriorly in the lateral wall of the cavernous sinus in the middle cranial fossa to the medial part of the superior orbital fissure. Before its entrance into the orbit through the superior orbital fissure, the ophthalmic nerve divides into three branches: frontal, nasociliary, and lacrimal.

        The frontal nerve is the largest branch of the ophthalmic division and travels anteriorly in the orbit, terminating as the supratrochlear and supraorbital nerves. The supratrochlear nerve lies medial to the supraorbital nerve and supplies the skin and conjunctiva of the medial portion of the upper eyelid and skin over the lower forehead close to the midline. The supraorbital nerve supplies the skin and conjunctiva of the central portion of the upper eyelid, the skin of the forehead, and the scalp as far back as the parietal bone and lambdoid suture.

        The nasociliary branch travels along the medial aspect of the orbital roof, giving off various branches. The nasal cavity and the skin at the apex and ala of the nose are innervated by the anterior ethmoid and external nasal nerves. The mucous membrane of the anterior portion of the nasal septum and lateral wall of the nasal cavity are innervated by the internal nasal nerve. The skin of the lacrimal sac, lacrimal caruncle, and adjoining portion of the side of the nose are innervated by the infratrochlear branch. The ethmoid and sphenoid sinuses are supplied by the posterior ethmoidal nerve. The eyeball is innervated by the short and long ciliary nerves.

        The lacrimal nerve supplies the skin and conjunctiva of the lateral portion of the upper eyelid and is the smallest branch of the ophthalmic division.

Maxillary Division

The maxillary division (V₂) of the trigeminal nerve is also a purely sensory division. Arising from the trigeminal ganglion in the middle cranial fossa, the maxillary nerve travels forward along the lateral wall of the cavernous sinus. Shortly after stemming from the trigeminal ganglion, the maxillary nerve gives off the only branch within the cranium; the middle meningeal nerve. It then leaves the cranium through the foramen rotundum, located in the greater wing of the sphenoid bone. After exiting the foramen rotundum, the nerve enters a space located behind and below the orbital cavity known as the pterygopalatine fossa. After giving off several branches within the fossa, the nerve enters the orbit through the inferior orbital fissure, at which point it becomes the infraorbital nerve. Coursing along the floor of the orbit in the infraorbital groove, the nerve enters the infraorbital canal and emerges onto the face through the infraorbital foramen.

        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 pterygopalatine nerves are two short nerves that merge within the pterygopalatine ganglion and then give rise to several branches. They contain postganglionic parasympathetic fibers, which pass along the zygomatic nerve to the lacrimal nerve innervating the lacrimal gland, as well as sensory fibers to the orbit, nose, palate, and pharynx. The sensory fibers to the orbit innervate the orbital periosteum.

        The posterior aspect of the nasal septum, mucous membrane of the superior and middle conchae, and the posterior ethmoid sinus are innervated by the nasal branches. 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. After descending through the pterygopalatine canal, the greater palatine nerve exits the greater palatine foramen onto the hard palate. The nerve 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 before the maxillary nerve enters 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 first molar.^1,2 Several dissection studies have been performed tracing the innervation of the first molar back to the parent trunk. These studies have demonstrated the variations in innervation patterns of the first molar and this is of clinical significance when anesthesia of this tooth is desired.

        In a study by Loetscher and Walton,³ 29 human maxillae were dissected to observe innervation patterns of the first molar. The study evaluated the innervation patterns by the posterior, middle, and anterior superior alveolar nerves on the first molar. The posterior and anterior superior alveolar nerves were found to be present in 100% (29/29) of specimens. The middle superior alveolar (MSA) nerve was found to be present 72% of the time (21/29 specimens). Nerves were traced from the first molar to the parent branches in 18 of the specimens. The PSA nerve was found to provide innervation in 72% (13/18) of specimens. The MSA nerve provided innervation in 28% (5/18) specimens, whereas the anterior superior alveolar nerve did not provide innervation to the first molar in any of the specimens. In the absence of the MSA nerve, the PSA nerve may provide innervation to the premolar region. In a study by McDaniel,⁴ 50 maxillae were decalcified and dissected to demonstrate the innervation patterns of maxillary teeth. The PSA was found to innervate the premolar region in 26% of dissections, when the MSA was not present. Table 20-1 lists the branches of the ophthalmic, maxillary, and mandibular divisions.

        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 MSA nerve descends along the lateral wall of the maxillary sinus to innervate the first and second premolar teeth. It provides sensation to the periodontal ligament, pulpal tissues, gingival, and alveolar process of the premolar region as well as the mesiobuccal root of the first molar in .some cases.^1,2 In a study by Heasman,⁵ dissections of 19 human cadaver heads were performed and the MSA was found to be present in seven of the specimens. Loetscher and Walton³ found that the mesial or distal position at which the MSA nerve joins the dental plexus (an anastomosis of the posterior, middle, and anterior superior alveolar nerves described below) determines its contribution to the innervation of the first molar. Specimens in which the MSA joined the plexus mesial to the first molar were found to have innervation of the first molar by the PSA and the premolars by the MSA. Specimens in which the MSA joined the plexus distal to the first molar demonstrated innervation of the first molar by the MSA. In its absence, the premolar region derives its innervation from the PSA and anterior superior alveolar nerves.⁴ The anterior superior alveolar nerve descends within the anterior wall of the maxillary sinus. A small terminal branch of the anterior superior alveolar 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 anterior superior alveolar has been shown to provide innervation to the premolar teeth. In the previously mentioned study by McDaniel, the anterior superior alveolar was shown to provide innervation to the premolar region in 36% of specimens in which no MSA nerve was found.⁴

        The three superior alveolar nerves anastomose to form a network known as the dental plexus, which comprises 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.

Figure 20-2. Anatomy of the mandibular nerve.

        The infraorbital nerve divides into three terminal branches after emerging through the infraorbital foramen onto the face. The inferior palpebral, external nasal, and superior labial nerves supply sensory innervation to the skin of the lower eyelid, lateral aspect of the nose, and skin and mucous membranes of the upper lip, respectively.

Mandibular Division

The largest branch of the trigeminal nerve, the mandibular branch (V₃), is both sensory and motor (Figure 20-2). The sensory root 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 from 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. After branching off the main trunk, the nervus spinosus reenters the cranium along with the middle meningeal artery through the foramen spinosum. 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. It gives off two branches that supply the tensor tympani and tensor veli palatini muscles.

        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 crosses the superior portion of the parotid gland, ascending behind the temporomandibular joint and giving off several sensory branches to the skin of the auricle, external auditory meatus, tympanic membrane, temporal region, temporomandibular joint, and parotid gland via postganglionic parasympathetic secretomotor fibers from the otic ganglion.

Figure 20-3. Breech-loading, metallic, cartridge-type, aspirating syringe.

        The lingual nerve travels inferiorly in the pterygomandibular space between the medial aspect of the ramus of the mandible and the lateral aspect of the medial pterygoid muscle. It then travels anteromedially below the inferior border of the superior pharyngeal constrictor muscle deep to the pterygomandibular raphae. The lingual nerve then continues anteriorly in the submandibular region along the hyoglossus muscle, crossing the submandibular duct inferiorly and medially to terminate deep to the sublingual gland. 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. lust before entering the mandibular canal, the inferior alveolar nerve gives off a motor branch known as the mylohyoid nerve (discussed below). The nerve accompanies 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 that 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 to the skin of the chin and lower lip.

        The mylohyoid nerve branches off the inferior alveolar nerve before its entry into the mandibular canal. It travels within the mylohyoid groove and along the medial aspect of the body of the mandible to supply the mylohyoid muscle as well as the anterior belly of the digastric.^1,2

        EQUIPMENT FOR REGIONAL MAXILLARY & MANDIBULAR ANESTHESIA

        Administration of regional anesthesia of the maxilla and mandible is achieved via the use of a dental syringe, needle, and anesthetic cartridge. Several types of dental syringes are available for use. However, the most common is the breech-loading, metallic, cartridge-type, aspirating syringe. The syringe comprises a thumb ring, finger grip, barrel containing the piston with a harpoon, and a needle adaptor (Figure 20-3). A needle is attached to the needle adaptor that engages the rubber diaphragm of the dental cartridge (Figure 20-4). The anesthetic cartridge is placed into the barrel of the syringe from the side (breech-loading). The barrel contains a piston with a harpoon that engages the rubber stopper at the end of the anesthetic cartridge (Figure 20-5). After the needle and cartridge have been attached, a brisk tap is given to the back of the thumb ring to ensure that the harpoon has engaged the rubber stopper at the end of the anesthetic cartridge (Figure 20-6).

        Dental needles are referred to in terms of their gauge, which corresponds to the diameter of the lumen of the needle. Increasing gauge corresponds to a smaller lumen diameter. Needles of 25 and 25 gauge are most commonly used for maxillary and mandibular regional anesthesia and are available in long and short lengths. The length of the needle is measured from the tip of the needle to the hub. The conventional long needle is approximately 40 mm in length, whereas the short needle is approximately 25 mm. Variations in needle length do exist, depending on the manufacturer.

        Anesthetic cartridges are prefilled, 1.8-mL glass cylinders with a rubber stopper at one end and an aluminum cap with a diaphragm at the other end (Figure 20-7). The contents of an anesthetic cartridge are the local anesthetic, vasoconstrictor (anesthetic without vasoconstrictor is also available), preservative for the vasoconstrictor (sodium bisulfite), sodium chloride, and distilled water. The most common anesthetics used in clinical practice are the amide anesthetics, lidocaine and mepivacaine. Other amide anesthetics available for use are prilocaine, articaine, bupivacaine, and etidocaine. Esther anesthetics are not as commonly used, but remain available. Procaine, procaine plus propoxycaine, chloropro- caine, and tetracaine are some common esther anesthetics.

Figure 20-4. Needle-syringe assembling. A needle is attached to the needle adaptor.

Figure 20-5. A: Needle-syringe assembling. The anesthetic cartridge is placed into the barrel of the syringe from the side (breech loading). B: A piston with a harpoon engages the rubber stopper at the end of the anesthetic cartridge while the needle adaptor engages the rubber diaphragm of the dental cartridge.

        Additional armamentaria include dry gauze, topical antiseptic, and anesthetic. The site of injection should be made dry with gauze, and a topical antiseptic should be used to clean the area. Topical anesthetic is applied to the area of injection to minimize discomfort during insertion of the needle into the mucous membrane (Figure 20-8). Common topical preparations include benzocaine, butacaine sulfate, cocaine hydrochloride, dyclonine hydrochloride, lidocaine, and tetracaine hydrochloride.

Figure 20-6. A and B: Needle-syringe assembling: A brisk tap is given to the back of the thumb ring to ensure that the harpoon has engaged the rubber stopper at the end of the anesthetic cartridge. C: A fully loaded anesthetic syringe.

Figure 20-7. A: Dental cartridges. The rubber stopper is on the right end of the cartridge while the aluminum cap with the diaphragm is on the left end of the cartridge. B: Containers of dental anesthetic.

Figure 20-8. Topical anesthesia. Before injection, topical anesthetic can be applied on the mucosa in the area of an injection to minimize discomfort to the patient.

        Universal precautions should always be observed by the clinician; these include the use of protective gloves, mask, and eye protection. After withdrawing the needle when a block has been completed, the needle should always be carefully recapped to avoid accidental needle stick injury to the operator.¹

        Retraction of the soft tissue for visualization of the injection site should be performed with the use of a dental mirror or retraction instrument. This is recommended for all maxillary and mandibular regional techniques discussed below. Use of an instrument rather than one’s fingers helps to prevent accidental needle-stick injury to the operator.

        TECHNIQUES OF REGIONAL MAXILLARY ANESTHESIA

The techniques most commonly used in maxillary anesthesia include supraperiosteal (local) infiltration, periodontal ligament (intraligamentary) injection, PSA (posterior superior alveolar) nerve block, MSA (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 (Table 20-2). Of less clinical application are the maxillary nerve block and intraseptal injection.

Supraperiosteal (Local) Infiltration

The supraperiosteal or local infiltration is one of the simplest and most commonly used 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. Contraindications to this technique are the need to anesthetize multiple teeth adjacent to one another (in which case a nerve block is the preferred technique), acute inflammation and infection in the area to be anesthetized, and, less significantly, the density of bone overlying the apices of the teeth. A 25- or 27-gauge short needle is preferred for this technique.

Related posts:

Regional Anesthesia in the Patient with Preexisting Neurologic Disease. The History of Local Anesthesia. Stimulating Catheters. Ultrasound-Assisted Nerve Blocks in Adults. Cutaneous Blocks for the Upper Extremity. Cervical Plexus Block.