Oral Cavity Anatomy: Boundaries and Divisions

Oral Cavity Boundaries

• Lips and cheeks are oral cavity boundaries.
• The hard and soft palates and the oral diaphragm are also boundaries.
• The isthmus faucium provides another boundary.

Oral Cavity Divisions

• The vestibule includes the lips, cheeks, gums, and teeth.
• The oral cavity proper contains the alveolar arches, teeth, gums, oropharyngeal isthmus, hard and soft palates, and the mouth floor.
• The vestibule is continuous with the oral cavity proper behind the third molar teeth, in the retromolar space, when the teeth are apposed.

Lips

• Lips are externally covered by skin and internally by mucosa, with the orbicularis oris muscle, labial vessels, nerves, fibro-adipose connective tissue, and labial salivary glands in between.
• The skin transitions to mucosa at the vermilion border.
• The labial commissure is the corner of the mouth.
• The philtrum is a shallow vertical groove.
• The nasolabial sulcus laterally bounds the upper lip.
• The mentolabial sulcus forms the inferior boundary of the lower lip.
• The labial frenulum includes superior and inferior parts.
• The superior and inferior labial arteries supply the lips from the facial artery.
• Corresponding veins drain into the submental vein, which is larger than the facial vein.
• The submandibular and submental lymph nodes serve this area.
• Maxillary and mandibular nerves innervate the lips.

Cheeks

• Cheeks have skeletal muscles, adipose tissue, fibrous connective tissue, vessels, nerves, and buccal salivary glands.
• The transverse facial artery (superficial temporal artery), buccal artery, and infraorbital artery (maxillary artery) supply blood, with corresponding veins providing drainage.
• Submandibular and parotid lymph nodes are present.
• Maxillary and mandibular nerves provide innervation.

Gums (Gingivae)

• Gums are composed of dense, vascular fibrous tissue.
• They are firmly attached to the cement at the necks of teeth and the adjacent alveolar process.
• The superior and inferior labial arteries (from the facial artery) provide blood supply, with corresponding veins for drainage.
• Lymphatic drainage occurs via the submandibular and submental lymph nodes.
• Maxillary and mandibular nerves provide innervation.

Palate (Oral Roof): Structures

• The hard palate consists of the palatine processes of the maxillae (2/3 anterior) and the horizontal plates of the palatine bones (1/3 posterior).
• The soft palate is a mobile flap suspended from the hard palate's posterior border.
• The uvula is a median conical process projecting downwards from the soft palate's posterior border.
• A submucosa-lacking zone runs anteroposteriorly in the midline of the hard palate as the palatine raphe.
• Transverse palatine folds/rugae run laterally from the raphe in the anterior part of the hard palate.
• At the raphe's anterior end, the incisive papilla covers the incisive fossa.

Palatal Arches

• The palatoglossal arch contains the palatoglossus muscle.
• The palatopharyngeal arch contains the palatopharyngeus muscle.
• The isthmus of the fauces is the aperture between the oral cavity and oropharynx, guarded by palatoglossal folds on either side.

Blood Vessels and Nerves of the Palate

• The greater palatine artery (maxillary artery) and ascending palatine artery (facial artery), along with a palatine branch of the ascending pharyngeal artery supply the palate.
• The pterygoid and tonsillar plexuses drain it.
• Deep cervical lymph nodes are present.
• The sensory nerves include the greater palatine nerve, lesser palatine nerve, nasopalatine nerve (maxillary nerve), and glossopharyngeal nerve.

Palatine Aponeurosis

• The palatine aponeurosis consists of the expanded tendon of the tensor veli palatini muscle and encloses the musculus uvulae.
• It serves as an attachment for palatine muscles.

Muscles of the Soft Palate

• The muscles of the soft palate include the levator veli palatini, tensor veli palatini, palatoglossus, palatopharyngeus, and uvulae muscles.

Levator Veli Palatini Muscle

• Originates from the petrous part of the temporal bone and the cartilage part of the auditory tube.
• It inserts into the soft palate and the upper surface of the palatine aponeurosis.
• It's innervated by the pharyngeal plexus.
• This muscle elevates the soft palate.

Tensor Veli Palatini Muscle

• Originates from the scaphoid fossa and the spine of the sphenoid and the cartilage part of the auditory tube.
• It inserts into the palatine aponeurosis.
• The mandibular nerve innervates it.
• This muscle elevates and tenses the soft palate.

Palatoglossus Muscle

• Originates from the palatine aponeurosis.
• Inserts on the sides of the tongue, with fibers spreading over the dorsum of the tongue.
• Runs within the palatoglossal arch.
• Elevates the root of the tongue; approximates the palatoglossal arch to the opposite side.

Palatopharyngeus Muscle

• Originates from the hard palate and palatine aponeurosis.
• It Inserts on the sides of the pharynx, at the posterior border of the thyroid cartilage.
• Runs within the palatopharyngeal arch.
• This muscle pulls the pharynx upward and medially, shortening it during swallowing.

Musculus Uvulae

• Originates from the posterior nasal spine and palatine aponeurosis.
• It inserts into the mucosa of the uvula.
• The pharyngeal plexus innervates it.
• This muscle causes elevation and retraction of the uvula.

Oral Diaphragm

• The oral diaphragm forms the floor of the mouth.
• It consists of three suprahyoid muscles: mylohyoid, geniohyoid, and the anterior belly of the digastric.

Isthmus of the Fauces (Oropharyngeal Isthmus)

• Connects the oral cavity proper to the oropharynx.
• Bounded superiorly by the soft palate, inferiorly by the root of the tongue, and laterally by the palatoglossal arches.
• Palatine tonsils are located between the two palatine arches.

Teeth Number

• Deciduous teeth begin to appear in the 6th month and are all present between 2.5-3 years.
• There are 20 deciduous teeth: 2 incisors, 1 canine, and 2 molars in each quadrant.
• Permanent teeth total 32, with 8 in each quadrant.
• The adult set comprises 2 incisors, 1 canine, 2 premolars, and 3 molars in each quadrant.
• Permanent teeth replace deciduous teeth, starting around the 6th year.

Tooth Anatomy

• The crown is the visible part of the tooth, covered by hard, translucent enamel.
• The root is covered by yellowish bone-like cement.
• The crown and root meet at the neck (cervical margin).
• The tooth's bulk is yellowish avascular tissue called dentine.
• A central pulp cavity narrows in the root as the pulp canal, opening at the tip as the apical foramen, where blood vessels and nerves enter and exit.
• The root is surrounded by alveolar bone, with cement separated from the osseous socket (alveolus) by soft periodontal ligament.
• Interalveolar septum separates bone between alveoli
• Interradicular septum separates bone between roots

Blood Vessels and Nerves of the Teeth

• Upper jaw blood supply: posterior superior alveolar artery; anterior superior alveolar arteries (both from maxillary artery)
• Lower jaw: inferior alveolar artery (maxillary artery)
• The veins follow the arteries.
• Lymphatic drainage goes to submandibular and deep cervical lymph nodes.
• Nerves of upper teeth: superior anterior alveolar nerve, superior middle alveolar nerve, and superior posterior alveolar nerve (all from maxillary nerve).
• Lower teeth nerve supply: inferior alveolar nerve (mandibular nerve).

Tongue

• The tongue is involved with deglutition, taste, and speech.
• It has both oral and pharyngeal positions.
• It attaches to the hyoid bone, mandible, styloid process, soft palate, and pharyngeal wall.
• Parts of the tongue: root, apex, dorsum (curved), and inferior surface.
• The dorsum is divided by a V-shaped sulcus terminalis into an anterior 2/3 (oral or presulcal) part and a posterior 1/3 (pharyngeal or postsulcal) part.
• Two limbs of the sulcus terminalis meet at the median foramen caecum (site of the upper end of the embryonic thyroid diverticulum).
• The tongue's inferior mucosa connects to the oral floor anteriorly by a median mucosal fold: the frenulum linguae.
• Lateral to the frenulum linguae are the deep lingual veins.
• Lateral to the deep lingual vein is a fringed mucosal ridge: the plica fimbriata.
• The pharyngeal part of the tongue is the base posterior to the palatoglossal arches and terminal sulcus.
• It has no papillae, but it has low elevations due to the lingual tonsil.
• Lingual papillae carry mucosa projections found on the presulcal part of the dorsum.
• The tongue has four types of papillae: filiform, fungiform, foliate, and vallate. All except the filiform have taste buds.

Lingual Papillae Types

• Filiform papillae at the lingual apex increase friction between the tongue and food (mechanical effect; no taste receptors; touch sense).
• These are the most numerous and smallest papillae. Long and thick filiform papillae become papillae conicae.
• Fungiform papillae occur mainly on the lingual margin but are also irregularly on the dorsum. They have large, rounded shapes and deep red color. Each usually bears one or more taste buds on their apical surface.
• Foliate papillae are formed by a series of red, leaf-like mucosal ridges at the tongue's sides, near the sulcus terminalis and bear are numerous taste buds.
• Vallate (circumvallate) papillae vary in number from 8-12 on the dorsum of the tongue. They form a V-shaped row in front of the sulcus terminalis and are 1-2 mm in diameter.

Muscles of the Tongue

• Extrinsic muscles: genioglossus, hyoglossus, styloglossus, and palatoglossus (soft palate).

Genioglossus Muscle

• Originates from the superior mental spine.
• Inserts on the post tongue; ventral surface of tongue; lingual aponeurosis; lingual septum.
• With forward traction of the apex, the tongue protrudes from the mouth. Acting bilaterally, the tongue's central part depresses. Acting unilaterally, the tongue diverges to the opposite side, protruding and depressing.
• Innervated by the hypoglossal nerve.

Hyoglossus Muscle

• Originates from the greater horn and body of the hyoid bone.
• It inserts into the side of the tongue, lingual aponeurosis.
• The action of this muscle is to depress the tongue
• Innervation is from the hypoglossal nerve.

Styloglossus Muscle

• Originates from the styloid process
• Inserts on the sides and posterior part of tongue.
• Draws tongue up and backwards.
• Innervated by the hypoglossal nerve.

Intrinsic Muscles of the Tongue

• Superior longitudinal: a thin stratum of oblique and longitudinal fibers beneath dorsal lingual mucosa.
• Inferior longitudinal: a narrow band close to inferior lingual surface between genioglossus and hyoglossus.
• Transverse lingual: fibers laterally from median fibrous septum to submucous fibrous tissue at lingual margin, blending with palatopharyngeus. Vertical lingual: extends from dorsal to ventral aspects of tongue in borders of its anterior part.
• The intrinsic muscles are innervated by the hypoglossal nerve.
• They alter the shape of the tongue:
  • The superior longitudinal muscle shortens the tongue and turns the apex and sides upwards.
  • The inferior longitudinal muscle shortens the tongue and pulls the apex down.
  • The transverse muscle narrows and elongates the tongue.
  • The vertical muscle makes the tongue flatter and wider.
• The lingual septum is a median fibrous partition and an attachment for the transverse lingual muscles.

Arteries of The Tongue

• Dorsal lingual branches and deep lingual arteries (lingual artery, from external carotid artery) supply the tongue.
• Root supplied by tonsillar and ascending palatine branches of facial arteries, ascending pharyngeal artery (from external carotid artery).

Veins of The Tongue

• Dorsal lingual veins drain dorsal and lateral parts, flow into the lingual vein, which empties into internal jugular vein.
• Deep lingual vein begins near the tip, runs back near the mucous membrane on the inferior surface. Near the anterior border of the hypoglossus muscle, it joins the sublingual vein (from salivary gland) → v. comitans nervi hypoglossi.
• V. comitans nervi hypoglossi joins facial, internal jugular, or lingual v.

Lymph Vessels of The Tongue

• Submental, juguloomohyoid, and submandibular
• Deep cervical

Nerves of The Tongue

• Palatoglossus muscle: Pharyngeal plexus
• All other motor: Hypoglossal nerve
• Sensory nn. of 2/3 anterior part (presulcal region): Lingual branch of mandibular n. (general sensation); Chorda tympani branch of facial n. that runs in the sheath of the lingual n.) (gustation).
• Sensory nn. of posterior part: Glossopharyngeal n. (general and gustatory sensation).
• Superior laryngeal n. (vagus n.) sends branches to the root, in the epiglottis front.

Salivary Glands

• Salivary glands include the submandibular gland (large), sublingual gland (small) and parotid gland.

Submandibular gland

• Consists of superficial (large) and deep (smaller) parts.
• The submandibular duct is about 5 cm long, originating from numerous tributaries in the superficial gland's part.
• Continuous with each other around posterior border of mylohyoid m.
• It Passes between the sublingual gland and the genioglossus and opens in the mouth on the summit of sublingual papilla (side of frenulum of tongue) → Sublingual caruncle.
• Situated in digastric triangle.

Blood Vessels and Nerves of Submandibular Gland

• Facial artery and lingual artery
• Same veins as arteries
• Deep cervical <juguloomohyoid<submandibul lymph nodes
• Lingual nerve
• Parasympathetic innervation: Chorda tympani (CNVII- Facial n)—By the chorda tympani, parasympathetic fibres' reach the lingual nerve and synapse in submandibular gang. and then reach the gland.
• Sympathetic innervation: Sympathetic trunk.
  • Sympathetic fibres synapse in the superior cervical gang, following the course around the arteries (external carotid) to reach the gland.

Sublingual Gland

• Lies beneath the oral mucosa, each in contact with sublingual fossa on lingual aspect of mandible where symphysis menti is close
• 3-4 gr.
• Has a raised mucosa of the oral floor (sublingual fold).

Excretory Ducts of Sublingual Gland

• 8-20 in number
  • Smaller sublingual ducts open separately on summit of sublingual fold; a few sometimes into/ near the submandibular duct
  • A single small major(or greater) sublingual duct (of Bartholin) opens beside orifice of submandibular duct located on the sublingual caruncle