Introduction

An understanding of the management of pain in dentistry requires a thorough knowledge of the Vth cranial nerve, which is the Trigeminal Nerve.

• The trigeminal nerve is composed of a small motor root and a considerably larger sensory root.
• It is developed in association with the first branchial arch.

Nuclei of Trigeminal Nerve

• It has 1 motor and 3 sensory nuclei.
• Motor nucleus is located in the pons and sends motor fibers via the mandibular nerve, which is a branch of the trigeminal nerve, in order to control the eight muscles, including the muscles of mastication.
• The main sensory nucleus is present in the pons.
• The midbrain contains the mesencephalic sensory nucleus of the trigeminal nerve for proprioception, while the spinal sensory nucleus of the trigeminal nerve has neuron bodies extending into the spinal cord, which carries pain and temperature.

Roots and Division of Trigeminal Nerve

Motor Root:

• The motor root of the nerve arises separately from the sensory root, originating in the motor nucleus within the pons.
• Its fibers, travel anteriorly along with the sensory root but separately.
• At the semilunar (gasserian) ganglion, the motor root passes in an inferio-lateral direction, under the ganglion, towards the foramen ovale, by which it leaves the middle cranial fossa along with the mandibular nerve.
• And just after leaving the skull, the motor root unites with the sensory root of the mandibular division to form a single nerve trunk.

Sensory Root:

• Sensory root fibers of the trigeminal nerve are located in the gasserian (trigeminal) ganglion.
• These ganglia are located in Meckel’s cavity, on the anterior surface of the petrous portion of the temporal bone.
• The trigeminal ganglion consists of cell bodies of sensory fibers that distribute along the following 3 divisions:

1. Ophthalmic Division (V₁):

• Travels anteriorly in the lateral wall of the cavernous sinus to the medial part of the superior orbital fissure, through which it exits the skull into the orbit.

2. Maxillary Division (V₂):

• Exits the cranium through the foramen rotundum into the upper portion of the pterygopalatine fossa.

3. Mandibular Division (V₃):

• Along with the motor root, exits the skull through the foramen ovale.

Division / Distribution	Branches
1. Motor Root Fibers Supplies the following muscles Muscles of mastication Masseter Temporalis Pterygoideus medialis Pterygoideus lateralis Mylolohyoid Anterior belly of Digastric Tensor tympani Tensor veli palatine
2. Sensory Root i. Ophthalmic nerve (V1) Exclusively sensory and smallest of all the 3 divisions. Passes through superior orbital fissure into the orbit Supplies cornea, superior conjunctiva, mucosa of anterosuperior nasal cavity, frontal, ethmoidal & sphenoidal air sinuses, anterior & supratrochlear duromater, skin of dorsum of external nose, superior eyelid, forehead, and anterior scalp. 🔍 Frontal nerve is the largest branch of ophthalmic division. 🔍 Lacrimal nerve is the smallest branch of ophthalmic division.	Nasociliary nerve Sensory root of ciliary ganglion Short ciliary nerve Long ciliary nerve Anterior & posterior ethmoidal nerves Infratrochlear nerve Frontal nerve Supratrochlear nerve Supraorbital nerve Lacrimal nerve Communicating branch from zygomatic nerve

Maxillary Nerve (V₂) – Distribution

Branches

Maxillary nerve (V₂) Originates from the middle of the trigeminal ganglion Sensory in function Passes through foramen rotundum to enter pterygopalatine fossa It is of intermediate size between the ophthalmic & mandibular division. It supplies dura mater of the anterior part of the middle cranial fossa. Skin of: Middle portion of the face Lower eyelid Side of the nose Upper lip Mucous membrane of: Nasopharynx Maxillary sinus Soft palate Tonsils Hard palate Maxillary teeth & periodontal tissues

Branches within the cranium Middle meningeal nerve Branches within the pterygopalatine fossa Zygomatic nerve Zygomaticotemporal nerve Zygomaticofacial nerve Pterygopalatine ganglion Orbital branches Nasal branches Nasopalatine nerve Palatine branches Greater (anterior) palatine nerve Lesser palatine nerve (middle & posterior) Pharyngeal branch Branches within the infraorbital canal Middle superior alveolar nerve Anterior superior alveolar nerve Branches on the face Inferior palpebral branches External nasal branches Superior labial branches

Mandibular Nerve (V₃) – Distribution

Branches

Mandibular nerve (V₃) It is the largest branch of the trigeminal nerve. It is a mixed nerve with 2 roots: a large sensory root and a smaller motor root. Passes through foramen ovale into the infratemporal fossa. Areas innervated include: Sensory Root Skin of: Temporal region Auricular External auditory meatus Cheek Lower lip Lower part of the face (except angle of the jaw, supplied by great auricular nerve (C2, C3)) Mucous membrane of: Cheek Tongue (anterior 2/3rd) Mastoid cells Mandibular teeth & periodontal tissues Bone of the mandible TMJ Parotid gland Motor Root Masticatory muscles Masseter Temporalis Pterygoideus lateralis Pterygoideus medialis Mylohyoid Anterior belly of digastric Tensor tympani Tensor veli palatini

Branches from the Undivided Nerve Nervus spinosus Nerve to the medial pterygoid muscle (motor nerve) Branches from the Divided Nerve From the anterior division Nerve to the lateral pterygoid muscle Nerve to the masseter muscle Nerve to the temporal muscle Buccal nerve (sensory nerve) From the posterior division Auriculotemporal nerve Lingual nerve Mylohyoid nerve Inferior alveolar nerve; dental branches Incisive branch; dental branches Mental nerve

High-Yield Pointers:

• Lesion of the trigeminal nerve causes sensory loss on the face and weakness of the muscles of mastication, which manifests as a deviation of the mandible toward the side of the lesion.
• Lesion of the lingual nerve near the neck of the third molar causes loss of general sensation and taste to the anterior two-thirds of the tongue, as well as salivary secretion from submandibular and sublingual glands (due to loss of preganglionic parasympathetic fibers from the chorda tympani branch of CN VII).
• Lesion of the ophthalmic division cannot mediate the afferent limb of the corneal reflex by way of the nasociliary branch (the facial nerve mediates the efferent limb).
• Lesion of the maxillary division cannot mediate the afferent limb of the sneeze reflex (vagus nerve mediates the efferent limb).
• Lesion of the mandibular division would be associated with loss of both the afferent and efferent limbs of the jaw jerk reflex.
• Trigeminal neuralgia (tic douloureux) is marked by paroxysmal pain along the course of the trigeminal nerve, especially radiating to the maxillary or mandibular area.
• The common causes of this disorder are aberrant blood vessels, aneurysms, chronic meningeal inflammation, brain tumors compressing on the trigeminal nerve at the base of the brain, and other lesions such as multiple sclerosis.
• If medical treatments are not effective, the neuralgia may be alleviated by sectioning the sensory root of the trigeminal nerve in the trigeminal (Meckel) cave in the middle cranial fossa.
• Abscess or infection of the maxillary teeth irritates the maxillary nerve, causing upper toothache.
• It may result in symptoms of sinusitis, with pain referred to the distribution of the maxillary nerve.
• Abscess or infection of the mandibular teeth might spread through the lower jaw to emerge on the face or in the floor of the mouth.
• It irritates the mandibular nerve, causing pain that may be referred to the ear, because this nerve also innervates a part of the ear.