Oral Cavity Nerve Supply & Anatomy: Study Notes

Chairside Support During Oral Health Assessment

  • H4PW 04 Unit Code: This standard is intended for individuals providing chairside support during the assessment of a patient's oral and general health.
  • Preparation: This role requires preparing all necessary equipment, instruments, materials, and medicaments for the assessment.
  • Support During Assessment: Close support involves:
    • Recording and charting information obtained from examining the head, neck, teeth, periodontium, and soft tissues.
    • Interpreting or anticipating the need for further equipment, instruments, materials, and medicaments.
  • Essential Components:
    • Effective communication with patients and other oral health care team members.
    • Promoting patient health, safety, and well-being.
  • Applicability: This standard applies to oral health workers in chairside support roles.
  • Best Practice: Users must ensure their practice reflects up-to-date information and policies.

The Temporomandibular Joint (TMJ)

  • Location: The TMJ connects the temporal bone of the skull to the mandible (lower jaw).
  • Components:
    • Condyle: The rounded projection on the mandibular head.
    • Temporal Bone: The part of the skull it articulates with.
    • Glenoid Fossa (Mandibular Fossa): A depression in the temporal bone where the condyle sits.
    • Articular Disc (Meniscus): A fibrocartilaginous disc located between the condyle and the glenoid fossa, allowing smooth movement and absorbing stress.
  • Muscles of Mastication: The lateral pterygoid muscle (4) is specifically identified as contributing to TMJ function and positioning of the articular disc.
  • Basic Premises of Function:
    • When the mandible closes, there is an ideal way for the teeth to contact.
    • There is an ideal place for the condyle and disc to be situated within the joint.
  • Conditions Affecting the TMJ:
    • Subluxation ("lock jaw"): A partial dislocation where the joint surfaces are still in contact but are out of normal alignment. The jaw may temporarily lock open.
    • Dislocation: Complete displacement of the condyle from the glenoid fossa, often requiring manual reduction (repositioning).

Bone Structures of the Maxilla and Mandible

  • Key Bones Identified:
    • Frontal Bone: Bone forming the forehead.
    • Mandible: The lower jaw bone.
    • Temporal Bone: Bone forming part of the side and base of the skull, housing the TMJ.
    • Zygoma (Zygomatic Bone): The cheekbone.
    • Maxilla: The upper jaw bone.
    • Nasal Bone: Forms the bridge of the nose.
    • Sphenoid Bone: A complex, butterfly-shaped bone at the base of the skull.
    • Parietal Bone: Bones forming the top and sides of the skull.
    • Occipital Bone: Bone forming the back and base of the skull.
  • Specific Mandibular Features (Illustrated):
    • Condyle: Articulates with the temporal bone.
    • Coronoid Process: A triangular projection on the anterior-superior aspect of the ramus.
    • Sigmoid Notch (Mandibular Notch): The concavity between the coronoid process and the condyle.
    • Alveolar Process: Part of the mandible that supports the lower teeth.
    • Body: The horizontal part of the mandible.
    • Ramus: The vertical part of the mandible.
    • Angle: The junction between the body and the ramus.
    • Lingula: A small projection anterior to the mandibular foramen.

The Foramina (Foramen)

  • Definition: Openings in bones that allow nerves, blood vessels, and ligaments to pass through.
  • Mandibular Foramen: An opening on the medial surface of the mandibular ramus through which the inferior alveolar nerve and vessels enter the mandible.
  • Lingula: A small tongue-shaped projection located just anterior to the mandibular foramen.
  • Mental Foramen: An opening on the outer surface of the mandible, typically below the apices of the premolars, through which the mental nerve and vessels exit. It is located approximately below teeth (4) and (5).
  • Palatine Bone: A L-shaped bone forming part of the hard palate, nasal cavity, and orbit.
  • Incisive Foramen: An opening in the anterior midline of the hard palate, posterior to the maxillary central incisors, through which the nasopalatine nerve passes.
  • Greater Palatine Foramen: An opening located on the posterior lateral aspect of the hard palate, through which the greater palatine nerve and vessels pass.
  • Lesser Palatine Foramen: Smaller openings posterior to the greater palatine foramen, transmitting lesser palatine nerves and vessels.
  • Infraorbital Foramen: An opening located below the orbit, on the anterior surface of the maxilla.
  • Supraorbital Foramen: An opening on the superior rim of the orbit.

Nerve Supply to the Oral Cavity

  • General Principles:
    • All nerves supplying the oral cavity originate directly from the brain as cranial nerves.
    • Nerves for the rest of the body run from the spinal cord as systemic nerves.
    • Cranial nerves can be sensory, motor, or a combination of both.
    • There are twelve pairs of cranial nerves leaving the brain.
    • Four pairs are highly relevant to dentistry.
  • Types of Nerves:
    • Motor Nerves: These nerves make muscles and glands work. They control movements and actions by transmitting information from the brain and spinal cord to muscles.
    • Sensory Nerves: These nerves convey pain or other sensations. They relay information from the skin and muscles back to the spinal cord and brain, which is then processed to allow sensation (e.g., pain).

Relevant Cranial Nerves in Dentistry

1. Trigeminal Nerve (V Cranial Nerve)

  • Key Role: The primary nerve supplying the teeth, soft tissues of the oral cavity, and muscles of mastication.
  • Divisions: It divides into three main branches:
    1. Ophthalmic Branch (V1): Sensory.
    2. Maxillary Branch (V2): Sensory.
    3. Mandibular Branch (V3): Sensory and motor.
  • Ophthalmic Division (V1):
    • Type: Primarily sensory nerve.
    • Passage: Exits the skull through the superior orbital fissure.
    • Supplies: Soft tissues around the eye and upper face.
  • Maxillary Division (V2):
    • Type: Sensory nerve.
    • Passage: Exits the skull through the foramen rotundum.
    • Overall Supply: Upper teeth, maxilla, and upper area of the face.
    • Buccal Divisions (Superior Alveolar Nerves, running through the alveolar bone):
      • Anterior Superior Alveolar Nerve (ASA):
        • Supplies: Maxillary incisors (1, 2), canines (3), and the labial gingivae (gum tissue on the lip side) of these teeth.
        • Also supplies soft tissues of the upper lip and nostrils.
      • Middle Superior Alveolar Nerve (MSA):
        • Supplies: Maxillary premolars (4, 5) and the mesial (front) half of the first molar (6M).
        • Also supplies their associated buccal gingivae.
      • Posterior Superior Alveolar Nerve (PSA):
        • Supplies: The distal (back) half of the first molar (6D), second molar (7), and third molar (8).
        • Also supplies their associated buccal gingivae.
    • Palatal Divisions (running along the palate):
      • Nasopalatine Nerve:
        • Enters from: The incisive foramen.
        • Supplies: The palatal gingivae (gum tissue on the palate side) of the upper central incisors (1), lateral incisors (2), and the anterior half of the canines (3).
        • Note: Supplies only palatal gingiva, not the teeth themselves.
      • Greater Palatine Nerve:
        • Enters from: The greater palatine foramen.
        • Supplies: The palatal gingivae of the maxillary molars (6, 7, 8) and premolars (4, 5), as well as the posterior half of the canines (3).
        • Note: Supplies only palatal gingiva, not the teeth themselves.
  • Mandibular Division (V3):
    • Type: Sensory to lower teeth, mandible, lower face; motor to muscles of mastication.
    • Passage: Exits the skull through the foramen ovale.
    • Overall Supply: All lower teeth, lower lip, chin, and tongue (partial).
    • Motor Branch: Provides stimulation to the muscles of mastication.
    • Sensory Divisions:
      • Inferior Dental Nerve (IDN) (Main Trunk):
        • Path: Runs through the alveolar bone.
        • Enters from: The mandibular foramen.
        • Supplies: All lower teeth ((1 to (8))).
        • Also supplies the labial/buccal gingivae of the premolars (4, 5) and incisors (1, 2, 3) (but not the posterior buccal gingivae of molars).
        • Provides anesthesia to the body of the mandible, lower portion of the ramus, and anterior two-thirds of the tongue (sensory).
      • Lingual Nerve:
        • Path: Runs lingually (to the tongue side) alongside the inferior alveolar nerve.
        • Supplies: Lingual gingivae of all lower teeth ((1 to (8))) and the floor of the mouth.
        • Provides touch sensation to the anterior two-thirds of the tongue.
        • Note: This nerve does not supply the teeth.
      • Long Buccal Nerve:
        • Path: Runs buccally (to the cheek side), branching off from the IDN.
        • Supplies: Buccal gingivae of the lower molars (6, 7, 8).
        • Note: This nerve does not supply the teeth.
      • Mental Nerve:
        • Path: Branches off from the inferior dental nerve and exits the mandible through the mental foramen.
        • Supplies: Buccal gingivae of the lower incisors (1, 2), canines (3), premolars (4, 5) and soft tissues of the lower lip and chin.

2. Facial Nerve (VII Cranial Nerve)

  • Type: Both sensory and motor components.
  • Supplies:
    • Some salivary glands.
    • The muscles of facial expression.
    • Parts of the tongue (taste sensation for anterior two-thirds).
  • Clinical Condition:
    • Bell's Palsy: A condition of temporary paralysis of the facial nerve, leading to acute facial nerve paralysis. It is the commonest type of facial palsy, affecting one side of the face (LMN Lesion). It is idiopathic (of unknown cause) but linked to inflammation of the facial nerve, preventing correct signal transmission. Signs and symptoms include smoothing of the forehead, inability to close eyelids, drooping mouth corner, unilateral facial weakness, loss of taste, and decreased salivation and tear secretion.

3. Glossopharyngeal Nerve (IX Cranial Nerve)

  • Supplies:
    • The throat (pharynx).
    • Parts of the tongue (posterior one-third for taste and general sensation).
    • Other salivary glands (parotid gland).

4. Hypoglossal Nerve (XII Cranial Nerve)

  • Type: Primarily motor nerve.
  • Supplies: Essential for the movement of the tongue, innervating both extrinsic and intrinsic muscles of the tongue.
  • Etymology: Its name is derived from ancient Greek, where 'hypo' means under, and 'glossal' means tongue.

Blood Supply to the Teeth and Gingivae

  • Arterial Supply: The teeth and gingivae are supplied by branches of the external carotid artery.
  • Venous Drainage: The veins draining the area eventually join the superior vena cava, which then enters the right side of the heart. From there, deoxygenated blood is pumped to the lungs for reoxygenation.

Study Tips

  • Self-Study: Actively engage with the material.
  • Visualization: Look at and redraw anatomical diagrams to reinforce understanding of bone structures, foramina, and nerve pathways.
  • Confidence Building: Regularly assess your understanding of the bone structures and nerve supplies.
  • Recap and Discussion: Discuss the nerve supply with peers or mentors to solidify knowledge.