Importance Of Structure And Function

An ideal reconstruction of the oral cavity is one that very closely resembles the original structures in both form and function. To approach this ideal, the interactions between structures both within and beyond the oral cavity must be considered (Fig. 1). Furthermore, advanced reconstructive techniques typically require utilizing or transversing structures adjacent to the oral cavity. Thus, a detailed understanding of both the structures within the oral cavity, and those related to it, is necessary to achieve the best reconstructive results.

Frenulum of upper lip Hard palate

Soft palate and urula

(Tonsil) palatine

Palatoglossal x arch

Soft palate and urula

(Tonsil) palatine

Palatoglossal x arch

Purpose Palatine Arches

Palato pharyngeal arch Palatine tonsil

Dorsum of tongue

Gingiva (gum)

Apex of tongue

Vestibule of mouth

Frenulum of lower lip

Figure 1 Anterior and intra-oral view of the oral cavity.

Dorsum of tongue

Palato pharyngeal arch Palatine tonsil

Gingiva (gum)

Apex of tongue

Vestibule of mouth

Frenulum of lower lip

Figure 1 Anterior and intra-oral view of the oral cavity.

Lips

The lips function as a sphincter, controlling ingress to and egress from the oral cavity. The full anatomic extent of the upper lip reaches superiorly to the base of the nose, and superolaterally to the deepest part of the nasolabial fold. The lower lip extends inferiorly to the labiomental groove. With relation to the oral cavity, however, the lip begins as the vermilion border and includes only those areas that are red in color. This red color is the result of blood being seen through a translucent mucous membrane, rather than from inherent red pigmentation. This is easily demonstrated by blanching the lip with pressure.

The upper lip skin contains a central groove, the philtrum, the lateral ridges of which end inferiorly at the labial tubercles of the upper lip. These tubercles contribute to the desirable cupid's bow shape to the upper lip. Displacement or effacement of the philtrum is quickly noticed; thus, this area represents an important region during lip reconstruction.

Beneath the lip skin is a layer of subcutaneous tissue with many muscles, nerves, and vessels (Fig. 2). This subcutaneous tissue lies just superficial to the orbicularis oris. The orbicularis oris provides the muscle tone and motion necessary for a competent oral sphincter. In addition to intrinsic muscle fibers, which run both circumferentially and obliquely from skin to mucosal membrane, the orbicularis is made of muscle fibers contiguous with the mentalis and buccinator muscles, as well as of fibers from the zygomaticus major, levator labii superioris, and depressor labii inferion. The contributions from the buccinator connect to muscle fibers extending from the commissures towards the maxillary or mandible alveolar ridges. These fibers form two commissures

Palatopharyngeal Arch

Depressor anguli oris muscle ^ Inferior labial artery

L Mentalis muscle L Depressor labii inferioris muscle

Figure 2 Frontal view of deep structures of the soft tissues of the face and lips.

Depressor anguli oris muscle ^ Inferior labial artery

L Mentalis muscle L Depressor labii inferioris muscle

Figure 2 Frontal view of deep structures of the soft tissues of the face and lips.

towards the maxillary or mandibular alveolar ridges. These fibers form two muscles, the incisivus labii superioris and inferioris. Buccal branches of the facial nerve innervate the orbicularis oris. The mentalis muscle, inferior to the orbicularis, receives innervation from the marginal mandibular branch of the facial nerve. Deficiency of mentalis function can be very noticeable in affecting lip position and function.

Blood supply to the lip is from the superior and inferior labial arteries that branch from the facial arteries, which run along the margin of the orbicularis oris deep to the vermilion of the lip. Deep to the orbicularis oris are numerous labial salivary glands, each with a small duct penetrating the mucosal membrane. The mucosal membrane forms a superior and inferior midline fold connecting to the alveolar gingiva, forming the superior and inferior labial frenulum.

Sensory supply to the lip arises from branches of the fifth cranial nerve. The infraoribtal nerves extend to the upper lip, and the mental nerve provides sensation to the lower lip. Lymphatic drainage is to the submental and submandibular lymph nodes, and can often be bilateral.

Buccal Mucosa and Cheek

The main structural component of the cheek is provided by the buccinator muscle. This muscle arises from the alveoli of the maxilla and mandible, as well as from the pterygomandibular raphe. This ligamentous raphe separates the superior constrictor muscle from the buccinator, and extends from the hamulus of the pterygoid to the mylohyoid line of the mandible. Anteriorly, the buccinator muscle extends to contribute to the orbicularis oris. Lateral to the buccinator is the buccal fat pad, which extends between the masseter and temporalis muscles. The buccinator muscle is pierced by the parotid duct that enters the oral cavity through the buccal mucosa across from the second maxillary molar. The buccinator muscle is continuous embry-ologically with the superior pharyngeal constrictor muscles. It is readily apparent that the external cheek skin covering, buccinator muscle, and buccal mucosa are

Nasal septum

Hard palate

Superior longitudinal muscle

Vertical and transverse muscles Styloglossus muscle Hyoglossus muscle

Genioglossus muscle Sublingual gland Submandibular duct Lingual nerve Lingual artery Mylohyoid muscle

Hyoid bone

Nasal septum

Buccal Fat Pad

Buccal mucosa Buccinator muscle Fat pad

Masseter muscle Skin

Platysma muscle Facial artery

Submandibular gland Lymph node Facial vein

Figure 3 A coronal image through the cheek showing the mucosa, muscle, fat pad, masseter, and a cross-section of the tongue and floor of mouth.

Buccal mucosa Buccinator muscle Fat pad

Masseter muscle Skin

Mandibular canal, inferior alveolar artery, vein, nerve

Platysma muscle Facial artery

Submandibular gland Lymph node Facial vein

Figure 3 A coronal image through the cheek showing the mucosa, muscle, fat pad, masseter, and a cross-section of the tongue and floor of mouth.

intimately related anatomically and functionally (Fig. 3). Buccal salivary glands are present in the submucosa, but are smaller than those in the lip.

Alveolar Ridges

The alveolar ridges represent bony extensions from the maxilla, superiorly, and mandible, inferiorly (Fig. 4). The teeth are present in alveolar sockets, and within these two ridges is a vascular mucosal membrane which is firmly attached by fibrous connective tissue. This mucosal membrane extends to be contiguous with the mucosa of the lips and buccal membranes, and also with the floor of mouth on the lingual side of the alveolar ridge, inferiorly, and with the hard palate, superiorly. Within the tooth sockets, the mucosa becomes contiguous with the periosteum.

Retromolar Trigone

The retromolar trigone (retromolar gingiva) is the term given to the tightly attached mucosa overlying the mandible from posterior to the first molar, along the ramus to the apex (Fig. 4). Tumors, such as those of the base of tongue or tonsillar fossa, onto the retromolar trigone must be carefully assessed for bone involvement as there is minimal tissue between the overlying mucosa and periosteum of the mandible.

Posterior Periosteum Lingual
Figure 4 Transoral view of the alveolar ridge, retromolar region, and mandible of the left side of the oral cavity.

Floor of Mouth

The floor of the mouth is a mucosal covered space that extends from the lingual surface of the mandibular alveolar ridge to the ventral surface of the tongue. Posteriorly, it extends to the base of the anterior tonsillar pillar. The left and right sides meet at the lingual frenulum along the anterior midline.

The underlying geniohyoid and mylohyoid muscles provide support for the floor of mouth. The mylohyoid muscle arises along the mylohyoid line of the mandible and inserts posteriorly into the hyoid and elsewhere into a median raphe. The geniohyoid is a paired midline muscle just superior to the mylohyoid. It originates along the posterior aspect of the symphysis at the mental spine and inserts on the hyoid. The floor of mouth is pierced anteriorly on either side of the lingual frenulum by the end of the submandibular duct forming the sublingual caruncle. Laterally, an elevation in the floor of mouth known as the sublingual fold represents the area of the underlying sublingual glands within the paralingual space (Fig. 5).

Also within the paralingual space courses the lingual nerve. This nerve arises from the mandibular division of the trigeminal nerve and courses across the subman-dibular duct to spiral around the duct from lateral to medial and then upward into the tongue (Fig. 6A). More medially, the hypoglossal nerve, cranial nerve XII, lies inferior (superficial) to the mylohyoid muscle before crossing the muscle into the tongue to supply motor innervation the intrinsic and extrinsic tongue musculature (Fig. 6B).

Hard Palate

The hard palate comprises the arched area extending from the inner portion of the superior alveolar ridge to the posterior edge of the palatine bone (Fig. 7). The bony

Submandibular ganglion

Lingual

Sublingual gland retracted

Frenulum

Sublingual fold

Sublingual nerve Submandibular gland

Oral Cavity Structures

Raphe RMT

Hypoglossal, n. Mylohyoid, m.

Mental neurovascular bundle

Submandibular duct

Sublingual duct (fold) orifices

Mucosa of tongue (retracted)

Photo Anterior Lingual Gland Cancer

Anterior lingual gland

Hyoglossus muscle

Inferior longitudinal muscle of tongue (cut and retracted)

Orifice of submandibular duct on sublingual papillae

Genioglossus muscle

Figure 5 Intra-oral view of the neurovascular structures of the tongue and floor of mouth with surface and deep anatomic details.

Submandibular ganglion

Lingual

Mucosa of tongue (retracted)

Anterior lingual gland

Hyoglossus muscle

(Deep lingual) artery nerve vein Plica fimbriata Frenulum Sublingual fold (orifices) ducts

Orifice of submandibular duct on sublingual papillae

Inferior lingual surface

Sublingual gland retracted

Lingual nerve branches to tongue

Raphe RMT

Hypoglossal, n. Mylohyoid, m.

Frenulum

Sublingual fold

Inferior longitudinal muscle of tongue (cut and retracted)

Genioglossus muscle

Mental neurovascular bundle

Submandibular duct

Sublingual nerve Submandibular gland

Sublingual duct (fold) orifices branches to isthmus of fauces

Hypoglossus muscle

Glossopharyngeal nerve post. 1/3 tongue IX

Glossopharyngeal Nerve

Lingual branches ant. 2/3 tongue

Inferior longitudinal, m.

Sublingual nerve Genioglossus, Geniohyoid, m.

Mylohyoid, m.

Lingual nerve

Submandibular ganglion

Sublingual orifices in fold and ducts to gland

Submandibular Gland Orofice

Orifice and duct to submandibular gland

Sublingual gland

Mylohyoid muscle and nerve Digastric, m.

Inferior alveolar nerve Mylohyoid nerve

(Submandibular gland) Superficial part

Deep part

Orifice and duct to submandibular gland

Sublingual gland

Mylohyoid muscle and nerve Digastric, m.

ant. belly with mylohyoid nerve

Styloglossus muscle Hypoglossal nerve Pharyngeal constrictor, m.

Hypoglossus muscle

Lingual nerve

Submandibular ganglion

Sublingual orifices in fold and ducts to gland

Glossopharyngeal nerve post. 1/3 tongue IX

Lingual nerve branches to isthmus of fauces

Mylohyoid, m.

Communicating branch (Hypoglossal nerve) Submandibular ganglion

Lingual branches ant. 2/3 tongue

Inferior longitudinal, m.

Sublingual nerve Genioglossus, Geniohyoid, m.

Figure 6 (A) View from right to left of the left interior oral cavity revealing detailed anatomy of salivary gland structures and neurovascular and muscular attachments. (B) View from right to left of interior right oral cavity revealing detailed neuromuscular anatomy of the tongue and floor of mouth.

Median palatine suture

Incisive foramen and nasopalatine nerve

Greater palatine foramen and nerve, a.

Lesser palatine foramina and nerve, a.

Median palatine suture

Incisive foramen and nasopalatine nerve

What Covers Nasopalatine Foramen

Zygomatic process

Posterior nasal spine Outline of uvula

Figure 7 View of the hard palate and anterior soft palate deep structures looking from inferior to superior.

Zygomatic process

Posterior nasal spine Outline of uvula

Figure 7 View of the hard palate and anterior soft palate deep structures looking from inferior to superior.

structure of the hard palate consists of the horizontal portions of the palatine bones and the palatine processes of the maxillae. These paired midline bones completely separate the oral cavity from the nasal cavity superiorly.

The bony structure is covered with periosteum tightly adherent to the overlying mucosa. Minor salivary glands, towards the posterior aspect of the hard palate, drain directly through the overlying mucosa into the oral cavity. Along the midline of the hard palate is the raised palatine raphe ridge, which ends anteriorly at the incisive papilla through which opens the incisive canal. This canal transmits sensory branches of the nasopalatine nerve to the anterior third of the hard palate. The posterior two-thirds of the hard palate receive sensory innervation through left and right greater palatine nerves, which penetrate the bony palate through left and right greater palatine foramina. These foramina lie along the lateral aspect of each of the horizontal parts of the palatine bones. The greater palatine branch of the maxillary artery also goes through the greater palatine foramen, traveling anteriorly on either side of the palate to meet branches of the sphenopalatine artery coming through the incisive canal. Lymphatic drainage is lateral to the tonsils towards the deep cervical nodes.

Although strictly part of the oral pharynx, the soft palate begins directly posterior to the hard palate at the posterior aspect of the horizontal palatine bones. The soft palate is a fold of mucous membranes containing muscle fibers, glands, nerves, and vessels. Laterally, the soft palate extends into the anterior (palatoglossal fold) and posterior (palatopharyngeal fold) tonsillar pillars. Between these, on either side, sits the palatine tonsil. A midline extension of the soft palate, the uvula, contains the musculus uvulae, which arises off of the palatine bones and soft palate aponeurosis. Many muscles contribute to the soft palate, including the levator veli palatini, tensor veli palatini, palatoglossus, palatopharyngeus, and musculus uvulae.

The tensor veli palatini is innervated by the mandibular branch of the trigerninal nerve, while these other muscles receive branches from the vagus through the phar-yngeal plexus.

Oral Tongue

The oral tongue is that area of the tongue anterior to the circumvallate papillae extending to the floor of mouth mucosa and is generally considered to represent the anterior two-thirds of the entire tongue. Separating the tongue into an anterior two-thirds and posterior one-third is legitimate as the two areas have different innervation, structure, and embryonic development. The division is the sulcus terminalis whose apex ends in the median foramen cecum. Anterior to the sulcus are 8-12 circumvallate papillae, each 1-2 mm wide and each with its own circumferential sulcus containing numerous taste buds.

The tongue is suspended by three bilateral attachments. On each side, there are connections to the mandible, hyoid bone, and styloid process. The tongue is also connected to the palate through the anterior tonsillar pillars, or palatoglossal arches. The midline of the tongue is incompletely divided by an areolar lingual septum that makes a relatively surgically bloodless plane of dissection. This midline septum is visible as a median sulcus along the dorsum of the tongue. Overall, the oral tongue is considered to have four parts: tip (or apex), lateral aspects, dorsum, and under-surface or ventral aspect.

The mucous membrane of the tongue has a rough surface that is distinct from the smooth surface of the floor of mouth or buccal mucosa. This roughness is a result of numerous papillae including fungiform papillae (present on the side and tip) and filiform papillae (prominent along the dorsum).

Tongue musculature is divided into intrinsic and extrinsic groups. The extrinsic groups include the genioglossus, styloglossus, and hyoglossus (Fig. 3). These serve to connect the tongue and move it relative to the three main bony attachments. The genioglossus arises from the mental spine of the symphysis before fanning along the inferior aspect of the tongue from the tip down to the hyoid. The styloglossus travels from the styloid process and stylomandibular ligament to lie predominantly superficially along the lateral aspects of the tongue extending to the tip. Some fibers travel through the hyoglossus towards the deep tongue. The hyoglossus arises from the hyoid bone and ascend into the tongue to run transversely, obliquely, and longitudinally.

Intrinsic tongue muscles lack origins or insertions outside of the body of the tongue. Their names are descriptive of their overall position and include the superior longitudinal muscles, inferior longitudinal muscles, transverse lingual muscles, and verticalis muscle.

Blood supply to the oral tongue is via the lingual artery, branching from the external carotid. Several branches that include the hyoid, dorsal lingual, deep lingual, and sublingual extend from the main lingual artery. Venous drainage is via the lingual veins, which meet the dorsal lingual veins to join the internal jugular. However, the vena comitans nervi hypoglossi travelling with the hypoglossal nerve is often larger than the lingual veins and drains into the facial vein.

Lingual lymphatics are rich and divided into four primary groups. The apical channels drain to the superior deep cervical chain, and specifically to the jugulo-omohyoid nodes, via the submental and submandibular nodes. Marginal channels drain around the sublingual gland to the submandibular nodes and superior deep cervical nodes near the digastric. Basal channels drain the posterior tongue into the jugulodigastric nodes, and the central channels drain between the genioglossus muscles to the superior deep cervical nodes. Median areas may drain bilaterally or contralaterally.

Muscular innervation is via the hypoglossal nerve. Taste sensation includes contributions from the seventh (chorda tympani), ninth (glossopharyngeal), and tenth (superior laryngeal) cranial nerves. General sensation is via the lingual nerve, branching from the trigeminal for the oral tongue, and via the ninth and tenth cranial nerves for the pharyngeal tongue (Fig. 6B).

Mandible

Although not specifically part of the oral cavity, the mandible contributes to the alveolar rides and retromolar trigone. The mandible is clinically divided into several regions including the condyle, condylar neck, coronoid process, ramus, angle, body, and symphysis (Fig. 8). Anteriorly, a protrusion along the lower border of the sym-physis forms the mental protuberance. The mental foramen, which transmits the mental nerve, is located on the right and left along the midportion of the mandible at the point of the second bicuspid tooth. In the mandible of the elderly edentulous patient, resorption of alveolar bone places the mental foramen in a relatively more superior location. An oblique line is palpable running inferior to the foramen to the ramus. This line can be of significance when using miniplates to reconstruct mandible fractures.

The mental spines are along the lingual surface of the mandible at the symphy-sis and provide attachment for the genioglossus muscles. The geniohyoid arises from a ridge just below this, and the mylohyoid along the inferior surface.

The ramus arises from the angle (an area of relatively thin bone) in a more vertical plane (approximately 110-120°). It provides attachments for the masseter along its lateral surface and for the medial pterygoid muscle on the medial surface. Also on the medial surface, the mandibular foramen allows for passage of the inferior alveolar nerve (off the third branch of the trigeminal nerve) and several blood vessels to enter the mandibular canal for travel towards the mental foramen. Several branches from the canal extend to each tooth socket.

The condylar neck is superior to the ramus and provides an insertion for the lateral pterygoid muscle. The condyle itself interfaces with the temporal bone at the temporomandibular joint. Anterior to the neck is a notch through which the masseter receives its neurovascular supply, and anterior to the notch is the coronoid process onto which the temporalis muscle inserts both laterally and medially.

Function

The oral cavity performs several critical functions. It has several specific roles in eating and processing of the food bolus. Beginning at the lips, proper sphincter function is necessary for delivery of food to the mouth and its containment during mastication. The tongue assists in mastication, along with the cheeks, by keeping food in the proper position to be chewed, and then helps deliver the bolus into the oral pharynx. Salivary glands, which drain into the oral cavity, contribute to formation of the food bolus, provide initial contact with digestive enzymes, as well as form a protective layer for the oral cavity mucosa and teeth.

Neuromuscular ForamenNeuromuscular Foramen

Buccal, n

Lingula

Neuromuscular Foramen

Mylohyoid line (ant. belly)

Digastric, m.

Figure 8 Detailed bony and neuromuscular anatomy of the mandible.

(Coronoid process)

x Temporalis, m Alveolar ridge

Mental protuberance

Inferior alveolar, a. and v.

Coronoid process and muscle insertion

Buccal nerve Buccinator, m.

Mental foramen

Inferior alveolar nerve

Mentalis, m

Facial, a

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Responses

  • J
    What is the function of the retromolar trigone in human?
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    What are the importance of vestibule?
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    What are the important of oral cavity?
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