The fifth pair of cranial nerves (V) called trigeminal nerve takes this name because it is divided into three main branches: ophthalmic (V1), maxillary (V2) and mandibular (V3). The latter represents the main branch because, unlike the other two carrying only afferent fibers, it also carries efferent fibers: it is, therefore, due to the mandibular nerve alone that the trigeminal can be called a mixed nerve. The V is also the largest of all cranial nerves, being responsible for serving with an eminently sensory role most of the face, the dental arches and support structures, most of the oral cavity and, in general, the structures of the mucous lining of the head.
The apparent origin of the nerve is located in the brainstem, exactly on the anterior face of the bridge near the middle cerebellar pedicle. The large, flattened sensory root is located laterally to the thin motor root, which is responsible for innervating the masticatory musculature, the anterior belly of the digastric muscle, the tensor of the tympanum and that of the palatine veil, as well as transporting facial nerve fibres (VII pair of cranial nerves) through the buccal nerve.
The neurons that make up the sensitive fibers have a trophic center site at the level of the semi-moon ganglion of the Gasser, located in a dimple (called the Meckel) subdural near the apex of the petrosal part of the temporal bone.
From the embryological viewpoint, the trigeminal forms the nerve of the first pharyngeal arch, the same origin of all the tributary muscles mentioned above.
The nerve leaves the endocranial space through the oval foramen located in the middle cranial fossa (sphenoid bone) and emerges in the infratemporal fossa. Still close to the base of the skull, the main trunk releases the sensory meningeal branch and some of the motor fibers, and then divides into a smaller anterior branch and a larger posterior branch.
It is estimated that one in five people may present some forms of variation limited to the mandibular branch and its branches: lower alveolar nerve (extra or intraosseous branches), lingual nerve (mainly positional anomalies), buccal nerve, auriculo-temporal nerve.
The mandibular nerve has a great significance in dental anesthesiology and oral and maxillofacial surgery. The course inside the infratemporal fossa is of considerable clinical interest not only because of the reduced accessibility of this space but also because of the compressive risk to which the nerve is exposed here.
In the final analysis, the nerve also falls within the chapter of atypical facial pain, of which trigeminal neuralgia is one of the most common forms: the mandibular and maxillary branches are the most commonly affected. The disease can lead to major limitations to the compensation of the patient’s health and is, for the doctor, difficult to interpret from a therapeutic viewpoint.