V3 – Mandibular Nerve
Figure 19. Cranial Nerve V3 – Mandibular Nerve
Unlike the first and second divisions of the trigeminal nerve the third division has a motor root in addition to the sensory one. The smaller motor root is separate from the sensory root as they pass through the foramen ovale which is the cranial exit of the mandibular nerve. Once through the opening they unite to form a single nerve. The motor component of the nerve is responsible for innervating the four muscles of mastication along with the mylohyoid, the tensor veli palatini, the tensor tympani, and the anterior belly of the digastric muscle. The sensory component carries sensory information from the mandible, the mandibular teeth, the periodontium and gingiva of the lower jaw as well as the skin overlying the mandible including the lower lip and the skin anterior to the ear plus some of the meninges surrounding the brain. As this is a motor nerve in addition to a sensory one we will start our tour of the nerve at the point where the two roots meet just past the foramen ovale.
Figure 20. Cranial Nerve V3 – Mandibular Nerve
In close proximity to the foramen ovale a number of branches of the nerve are seen. The closest to the foramen is the sensory meningeal branch carrying fibers originating in the meninges. The next branch is a mixed one that splits to form muscular branches and then continues as a sensory nerve. These are the nerves to the temporalis, masseteric , the nerve to the medial and lateral pterygoids. In addition, there are some very small branches serving the tensor tympani and tensor veli palatini. After these motor fibers leave the nerve continues as the buccal nerve carrying sensation from the cheek and facial gingiva posterior to the mental foramen. This nerve is generally referred to in dentistry as the long buccal nerve to distinguish it from an identically named buccal nerve that is a branch of the facial nerve.
Entering the mandibular nerve posteriorly is the auriculotemporal nerve which is the afferent nerve from the ear, the temporal region and the TMJ. In addition, this nerve carries parasympathetic fibers that originate from the glossopharyngeal nerve (cranial nerve IX) that it picks up while passing through the otic ganglion. These post-synaptic fibers provide innervation to the parotid gland.
The mandibular nerve then splits into two terminal branches, inferior alveolar and the lingual nerve which lie in close proximity to one another until the inferior alveolar nerve enters the mandible at the mandibular foramen. The lingual nerve is the sensory nerve for the anterior two-thirds of the tongue and the tissues on the lingual of the mandible. Like the auriculotemporal nerve it carries postganglionic fibers that originate elsewhere. In this case they are fibers from the facial nerve and are destined for the submandibular and sublingual salivary glands. These merge with the nerve at the submandibular ganglion (see facial nerve diagram) which is attached to the lingual nerve. To make matters more complicated as the general sensory fibers form the lingual nerve in the tongue and they are joined by fibers from the taste buds of the tongue. These fibers ultimately will join the chordae tympani which is the same branch of the facial nerve carrying parasympathetic fibers to the submandibular ganglion.
The other branch, the inferior alveolar nerve passes into the mandible through the mandibular foramen but prior to that gives off a couple of final motor branches, the nerve to the mylohyoid and the nerve to the anterior belly of the digastric. Once those branches have separated the remaining fibers are all afferent. The nerve passes through the mandible in a tunnel in the bone known as the mandibular canal. Throughout its passage it is joined by fibers carrying sensory fibers from the posterior teeth and the surrounding bone. At the other end of the canal is the mental foramen. This is the point at which the inferior alveolar nerve is formed by the union of the mental nerve which originates in the lower lip and facial gingiva, anterior to the mental foramen, plus the incisive nerve which consists of small branches that originate in the mandible and the teeth anterior to the mental foramen. This can be confusing as in the maxilla there is an incisive canal through which passes the nasopalatine nerves. The incisive nerve, however, remains within the mandible so there is no opening associated with it.