Topography of the Mandibular Nerve
The mandibular nerve (n. mandibularis) is the third branch of the trigeminal nerve and is of a mixed type, containing both sensory and motor fibers. Upon exiting the cranial cavity through the foramen ovale, the trunk enters the infratemporal fossa, where it immediately begins to divide into branches.
The motor portion heads toward the muscles of elevation of the mandible. This group includes the masseteric, deep temporal, as well as the lateral and medial pterygoid nerves. Notably, the masseteric nerve (n. massetericus) gives off a slender sensory branch to the temporomandibular joint (TMJ) before entering the muscle of the same name.
The sensory fibers are closely connected with autonomic ganglia (otic, submandibular, and sublingual), from which postganglionic parasympathetic pathways lead to the salivary glands.
Inferior Alveolar Nerve: The Primary Target
The largest branch is the inferior alveolar nerve (n. alveolaris inferior). It runs within the pterygomandibular space, located posterior and lateral to the lingual nerve.
Before entering the bone through the foramen mandibulae, the mylohyoid nerve branches off, heading toward the muscles of the floor of the mouth. Once inside the mandibular canal (canalis mandibulae), the main trunk gives off numerous branches that form the inferior dental plexus (plexus dentalis inferior). Nerves to the pulp of each tooth and gingival branches to the mucous membrane originate from the plexus.
At the level of the premolars, the trunk divides into:
- Mental nerve (n. mentalis) — exits through the mental foramen, providing sensation to the skin of the chin and lower lip.
- Incisive branch (ramus incisivus) — continues within the bone, innervating the canines and incisors, and forms an anastomosis at the midline with the corresponding branch from the opposite side.
Lingual Nerve and Its Features
The lingual nerve (n. lingualis) originates near the alveolar nerve but runs anterior to it. Near the upper margin of the medial pterygoid muscle, it is joined by the chorda tympani (chorda tympani). This branch carries taste fibers to the papillae of the tongue and secretory fibers to the salivary ganglia.
Next, the nerve passes above the submandibular gland, loops around its excretory duct, and penetrates the lateral surface of the tongue. When successful, its block results in anesthesia of the anterior 2/3 of the tongue, the mucosa of the fauces, the floor of the mouth, and the lingual gingiva of the mandible.
Buccal Nerve and the Problem of Torus Anesthesia
The buccal nerve (n. buccalis) descends inferiorly and laterally between the heads of the lateral pterygoid muscle. It is responsible for innervating the skin of the cheek, the angle of the mouth, and the area of the gingival mucosa on the vestibular side (usually from the second premolar to the second molar). The branching pattern of the nerve in the tissues can be either main-trunk or dispersed.
A critically important clinical nuance: the buccal nerve runs quite far from the main trunks in the connective tissue — at a distance of 22 mm from the lingual nerve and 27 mm from the inferior alveolar nerve. This is precisely why, during torus anesthesia (even with an abundant injection of 2–3 ml of anesthetic using Egorov's technique), the buccal nerve is not consistently blocked. An additional injection is often required to reliably anesthetize the vestibular gingiva.
Briefly: answers to topical questions
Specifically, which muscles does the mylohyoid nerve innervate?
The mylohyoid nerve innervates:
- Mylohyoid muscle (m. mylohyoideus) — forms the floor of the oral cavity.
- Anterior belly of the digastric muscle (m. digastricus).
Class and exam questions
Why might a patient feel pain on the cheek side during torus anesthesia?
The buccal nerve runs at a considerable distance (about 27 mm) from the inferior alveolar nerve. The standard volume of anesthetic injected into the retromolar trigone area is often insufficient to block it via diffusion.
Which branch is responsible for innervating the mandibular anterior teeth?
The canines and incisors are innervated by the incisive branch (ramus incisivus), which is the intraosseous continuation of the inferior alveolar nerve after the origin of the mental trunk.
Is motor function blocked during an inferior alveolar nerve block?
Partially yes. Before entering the canal, the mylohyoid nerve branches off to innervate the muscle of the same name. However, the muscles of mastication are not affected because their nerves branch off significantly higher up.
What else to study on this topic
- Motor branches of the mandibular nerve (masseteric, deep temporal, and pterygoid)
- Autonomic ganglia of the face and their connection to the third division of the trigeminal nerve
- Technique of maxillary tuberosity anesthesia
- Topography of the superior dental plexus
- Course and innervation area of the auriculotemporal nerve
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Other topics in "Chapter 12. Dental Anesthesia"
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