Boundaries of the oral region
The space of the oral region is clearly defined by natural landmarks and facial folds. Knowledge of these boundaries is essential for determining the localization of pathological processes.
- Superiorly: the boundary runs along a horizontal line drawn through the base of the nasal septum.
- Inferiorly: the region is bounded by a horizontal line running along the mentolabial sulcus.
- Laterally: the nasolabial folds serve as the lateral boundaries.
Topographic anatomy of the lips
The lips form the anterior wall of the oral cavity. Their free margins delimit the oral fissure and, meeting at the angles, form the corners of the mouth. Anatomically, the lips have a distinct layered structure (from outside to inside):
- Skin: notable for its thinness, contains a significant number of sebaceous and sweat glands.
- Vermilion border: serves as a transitional zone between the skin and the mucous membrane.
- Mucous membrane: laterally it continues into the buccal mucosa, and superiorly and inferiorly it transitions to the gingiva. Along the midline, the mucosa forms specialized folds — the frenula of the upper and lower lips (frenuli labii superior et inferior).
- Submucosa: formed by loose connective tissue. This layer contains mucous glands, as well as the superior and inferior labial arteries, accompanying veins, and nerve trunks.
- Muscle layer: the base is formed by the orbicularis oris muscle. An important topographic feature is that the skin is tightly fused with this muscle, making it relatively immobile relative to the muscle layer.
Innervation and lymphatic drainage
Motor and sensory innervation of the lips is provided by different cranial nerves, which is important to consider when assessing neurological status.
- Motor innervation: the orbicularis oris muscle is innervated by branches of the facial nerve — buccal branches (rr. buccales) and the marginal mandibular branch (r. marginalis mandibulae).
- Sensory innervation: provided by branches of the trigeminal nerve. The mucous membrane of the upper lip receives innervation from the superior labial branches (rr. labiales superiores, originating from the infraorbital nerve). The lower lip is innervated by the inferior labial branches (rr. labiales inferiores from the mental nerve).
Lymphatic drainage pathways: Lymphatic vessels from the upper lip and the outer two-thirds of the lower lip run along the facial artery and drain into the submandibular lymph nodes (nodi lymphatici submandibulares). Lymph from the middle third of the lower lip drains directly into the submental lymph nodes (nodi lymphatici submentales).
Oral vestibule and oral cavity proper
The oral cavity is divided into two communicating spaces.
Oral vestibule (vestibulum oris) Communicates with the oral cavity proper through the interdental spaces and through the free space located behind the last molars. In the vestibule, on the parotid papilla (papilla parotidea), strictly at the level of the second upper molar, the excretory duct of the parotid salivary gland (ductus parotideus) opens. On the anterior surface of the maxilla lies the superior transitional fold. Topographically adjacent to it are the buccal fat pad (corpus adiposum buccae) and the anterior border of the masseter muscle (m. masseter). On the anterior surface of the mandible, midway between the alveolar and inferior borders, beneath the mucous membrane lies the mental foramen (foramen mentale), transmitting the mental artery, vein, and nerve.
Oral cavity proper (cavitas oris propria) When the jaws are closed, it appears as a narrow slit.
- Boundaries: bounded inferiorly by the tongue, anteriorly and laterally by the teeth, and superiorly by the palate. Posteriorly, the cavity continues into the fauces (isthmus faucium), which opens into the oropharynx.
When the mouth is opened wide, one can observe a mucosal fold tightening behind the last molars — this corresponds to the sphenomandibular ligament (lig. sphenomandibulare).
Clinical anatomy of the maxilla
Special attention in dental surgery and maxillofacial surgery is paid to the topography of the maxillary premolars. The bone plate separating the roots of these teeth and the floor of the maxillary sinus is extremely thin. Due to this anatomical feature, purulent-inflammatory processes affecting the pulp or root of a premolar can easily destroy the bone barrier and spread to the sinus mucosa, causing odontogenic maxillary sinusitis.
Briefly: answers to topical questions
Which muscles participate in forming the floor (diaphragm) of the oral cavity?
The floor (diaphragm) of the oral cavity is formed by the mylohyoid muscle, as well as deep muscles of the oral floor.
- Mylohyoid muscle (m. mylohyoideus) — stretches between the hyoid bone and the mandible.
- Geniohyoid muscle (m. geniohyoideus) — rounded in shape, located above the m. mylohyoideus.
- Genioglossus muscle (m. genioglossus) — fan-shaped, runs from the mental spine to the root of the tongue.
- Hyoglossus muscle (m. hyoglossus) — lies posteriorly and laterally to the m. genioglossus.
What anatomical structures bound the fauces (isthmus faucium)?
The fauces (isthmus faucium) is an anatomical structure leading into the oropharynx, bounded by the soft palate, palatoglossal arches, and the dorsum of the tongue.
- Soft palate (Palatum molle) — forms the superior boundary of the fauces, shaped like an irregular quadrilateral with a projection in the middle (uvula).
- Palatoglossal arches — bound the fauces laterally.
- Dorsum of the tongue (dorsum linguae) — forms the inferior boundary of the fauces.
What groups of minor salivary glands are distinguished in the oral mucosa?
Five types of minor salivary glands are distinguished in the oral mucosa.
- Labial glands — localized in the submucosa of the corresponding areas.
- Buccal glands — localized in the submucosa of the corresponding areas.
- Lingual glands — localized in the submucosa of the corresponding areas.
- Palatine glands — localized in the submucosa of the corresponding areas.
- Molar glands — localized in the submucosa of the corresponding areas.
Physiologically, all these minor glands account for 31% of total daily saliva production.
Lymphatic drainage from the lower lip: "Edges to the jaw, center to the chin." The outer thirds drain lymph into the submandibular nodes, while the central part drains directly into the submental nodes.
Class and exam questions
How does the vestibule of the mouth communicate with the oral cavity proper when the jaws are clenched?
Communication occurs through the interdental spaces, as well as through the small space located behind the last molars (retromolar space).
Where does the excretory duct of the parotid salivary gland open?
The duct (ductus parotideus) opens into the oral vestibule on the parotid papilla, which projects at the level of the second upper molar.
Why is inflammation of the maxillary premolars often complicated by sinusitis?
This is due to the fact that the bone plate between the alveoli of the premolars and the floor of the maxillary sinus is extremely thin, which does not impede the spread of infection (leading to odontogenic maxillary sinusitis).
What else to study on this topic
- Topography and contents of the mental foramen (foramen mentale)
- Relationships between the superior transitional fold and the buccal fat pad
- Anatomical boundaries of the fauces (isthmus faucium) and oropharynx
- Projection and significance of the sphenomandibular ligament with the mouth open
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