Applied anatomy of Mouth

The mouth extends from the lips to the oropharyngeal isthmus which is the junction of the mouth with the pharynx. It is subdivided in to the vestibule, lying between lips and cheeks externally and gums and teeth internally and the mouth cavity proper which lies with in the alveolar arches, gums and teeth.

The vestibule is a slit like space that communicates with the exterior through the oral fissure. When the jaws are closed it communicates with the mouth proper behind the third molar tooth on each side. Superiorly and inferiorly the vestibule is limited by reflection of the mucous membrane from the lips and cheeks on to gums.

 The mouth proper has a roof , which is formed by the hard palate, in front and soft palate behind. The sensory nerve supply of the mucous membrane of the roof of the mouth is by greater palatine and nasopharyngeal nerve. The floor is formed largely by the anterior two third of the tongue and by the reflection of the mucous membrane from the sides of the tongue to the gum of the mandible. The mucous membrane of the floor of the mouth is supplied by lingual nerve , a branch of mandibular nerve.

The palate forms the roof of the mouth and is divided  in to the anterior hard palate and the posterior soft palate. The bones forming the hard palate are the maxilla and the palatine bones. The soft palate is muscular ,curves downwards from the posterior end of the hard palate and blends with the walls of the pharynx at the sides.

The uvula is a curved fold of muscle covered with mucous membrane , hanging down from the middle of the free border of the soft palate. Originating from the upper end of the uvula there are four folds of mucous membrane, two passing downwards at each side to form membranous arches. The posterior folds, one on each side are the palatopharyngeal arches and the two anterior folds are the palatoglossal arches. On each side , between the arches is a collection of lymphoid tissue called the palatine tonsil often referred to as “ the tonsil.”

The lips are mobile , musculofibrous folds surrounding the mouth, extending from the nasolabial sulci and nares laterally and superiorly to the mentolabial sulcus inferiorly. They contain the orbicularis oris and superior and inferior labial muscles, vessels and nerves. The lips are covered externally by skin and internally by mucous membrane. The blood supply of lips are by superior and inferior labial arteries ,branches of facial arteries. The lymphatic drainage of upper and lateral parts of lower lip passes primarily to the submandibular lymph nodes and medial part of the lower lip to the submental lymph nodes.

The cheek forms the lateral wall of the vestibule and is made up of the buccinator muscle, which is covered outside by fascia and skin and is lined by mucous membrane. Opposite the second upper molar tooth , a small papilla is present on the mucous membrane, marking the opening of the duct of parotid gland. The cheek is supplied by the buccal nerve , a branch of mandibular nerve.

Clinical significance of the examination of the mouth
The mouth is one of the important areas of the body we have to examine . The physician must be able to recognize all the structures visible in the mouth and be familiar with the variation in the color of the mucous membrane covering underlying structure.

•  The sensory nerve supply and lymphatic drainage of the cavity should be noted.
• The close relation of the lingual nerve to the lower third molar tooth should be noted.
• The close relation of the submandibular duct to the floor of the mouth helps to palpate a calculus in cases of periodic swelling of submandibular salivary gland.

The tongue
The tongue is a mobile muscular organ that can assume a variety of shapes and positions.  It is partly in the oral cavity and partly in the oropharynx. The tongue is involved with mastication, taste, deglutition, articulation,and oral cleaning. But its main function is forming words during speaking and squeezing food in to the oropharynx when swallowing.

Parts and surfaces of the tongue
The tongue has a root, a body, an apex, a curved dorsum, and an inferior surface. The root of the tongue is the part that rests on the floor of the mouth. It is usually defined as the posterior part of the tongue. The body of the tongue is the anterior two third of the tongue. The apex of the tongue is the anterior end of the body which rests against the incisor teeth. The body and apex of the tongue is extremely mobile.

The dorsum of the tongue is the posterosuperior surface which is located partly in the oral cavity and partly in the oropharynx. It is characterized by a ‘V’ shaped groove, the angle of which points posteriorly to the foramen caecum, which is the nonfunctional remanant of the proximal part of the embryonic thyroglossal duct. The terminal sulcus divides the dorsum of the tongue in to anterior part in the oral cavity proper and posterior part in the oropharynx. The margin of the tongue is related on each side to the lingual gingivae and the lateral teeth.

The mucous membrane of the anterior part of the tongue is rough because of the presence of the small lingual papillae. There are mainly four types of papillae.

• Vallate papillae: Large and flat topped. They lie directly anteriorly to the terminal sulcus and are arranged in a ‘v’ shaped row.
• Foliate papillae: small lateral folds of lingual membrane.
• Filiform papillae: Long and numerous , they contain afferent nerve endings that are sensitive to touch.
• Fungiform papillae: Most numerous at apex and margin of the tongue.
• The vallate ,foliate and most of the fungiform papillae contain taste receptors in the taste buds.

The mucous membrane of the posterior part of the tongue is thick and freely movable.It has no lingual papillae , but  the underlying lymphoid nodule , gives this part an irregular   cobble stone appearance The lymphoid nodules are collectively known as lingual tonsil.

The inferior surface of the tongue is covered with a thin transparent mucous membrane through which veins are seen. This surface is connected to the floor of the mouth by a midline fold called frenulum of the tongue. It allows the anterior part of the tongue to move freely. A sublingual caruncle is present on each side of the base of lingual frenulum.

Muscles of the tongue
The muscles of the tongue is divided in to two types, namely extrinsic and intrinsic.

Extrinsic muscles of the tongue: The extrinsic muscles are that originate outside the tongue and attach to it. The  muscles include genioglossus, hyoglossus, styloglossus, and palatoglossus. They mainly move the tongue but they can alter its shape as well.

Intrinsic muscles of the tongue: The intrinsic muscles are confined to the tongue and are not attached to bone. They consists of superior and inferior  longitudinal , transverse , and vertical muscles. They alter the shape of the tongue

1.superior longitudinalMedian septum and submucosa.Mucous membrane and margins of tongue.

HypoglossalCurls tip and sides of tongue superiorly and shortens tongue2.Inferior longitudinalRoot of tongue and body of hyoid bone.Apex of tonguehypoglossalCurls tip of tongue inferiorly and shortens tongue.3.TransverseMedian fibrous septumFibrous tissue at margins of tongueHypoglossalNarrows and elongates the tongue.4.VerticalSuperior surface of borders of tongue .Inferior surface of borders of the tongue.HypoglossalFlattens and broadens the tongue.

Blood supply of tongue
The main artery to the tongue is the lingual ,a branch of the external carotid artery .The dorsal lingual arteries provide the blood supply to the root of the tongue and a branch to the palatine tonsil. The deep lingual arteries supply the body of the tongue. The sublingual arteries provide the blood supply to the floor of the mouth , including the sublingual glands.

The veins of the tongue are the dorsal lingual veins ,which accompany the lingual artery ; the deep lingual veins , which begin at the apex of the tongue, run posteriorly beside the lingual frenulum to join the sublingual vein. All these lingual veins terminate in the internal jugular vein. 

Nerve supply of tongue
The anterior two third of the tongue are supplied by the lingual nerve for general sensation and by the chorda tympani , a branch of  the facial nerve for taste. The posterior third of the tongue and the vallate papillae are supplied by the lingual branch of the glossopharyngeal nerve for both general sensation and taste. Twigs of the internal laryngeal nerve , a branch of the vagus nerve ,supply mostly general but some special sensation to a small area of the tongue just anterior to the epiglottis.

There are four basic taste sensations: sweet, salty , sour, and bitter. Sweetness is detected at the apex of the tongue , saltness at the lateral margins, and sourness and bitterness at the posterior  part of the tongue.   

Lymphatic drainage of tongue

Lymph from the tongue takes takes four routes.

• (1)   Lymph from the posterior third drains in to the superior deep cervical lymph nodes.
• (2)   Lymph from the medial part of the anterior two third drains directly to the inferior deep cervical lymph nodes.
• (3)   Lymph from the lateral parts of the anterior two third drains to the sub mandibular lymph nodes.
• (4)   The apex and frenulum drain to the submental lymph nodes. 

Applied  anatomy

Gag reflex : It is possible to touch the anterior part of the tongue with out feeling discomfort. When the posterior part is touched, the individual gags. CN IX, CN X, are responsible for the muscular contractions of each side of the pharynx.

Paralysis of genioglossus: When this muscle is paralysed the tongue has a tendancy to fall posteriorly , obstructing the airway and preventing the risk of suffocation. Total relaxation of the genioglossus muscles occurring during general anesthesia therefore an airway is inserted in an anesthetized person to prevent the tongue from relapsing.

Injury to the hypoglossal nerve: Trauma , such as fractured mandible , may injure the hypoglossal nerve, resulting in paralysis and eventual atrophy of one side of the tongue.

A lingual carcinoma in the posterior part of the tongue metastases to the superior deep cervical lymph nodes on both sides, where as a tumor in the anterior part usually does not metastasize to the inferior deep cervical lymph nodes until late in the disease. Because these nodes are closely related to I J V, metastases from the tongue may be widely distributed.

Frenectomy: A large lingual frenulum (tongue tie) interefere with the tongue movements and may affect speech. In unusual cases a frenectomy in infants may be required.

Ulcers of the tongue:Various types of ulcers are follows(i) Aphthous ulcers: is  a small painful ulcer seen on tip , under surface of the tongue in its anterior part. (ii) Dental ulcer : is caused by mechanical irritation either by a jagged tooth or denture. (iii) Syphilitic ulcer: mainly snail track ulcers ulcers in second stage of syphilis.(iii) carcinomatous ulcers : It usually occurs in elderly individuals above the age of 5o years . Common site is at the margins particularly in anterior two third of the tongue.  

The teeth
The teeth are set in the tooth sockets and are used in mastication and in assisting in articulation. A tooth is identified and described on the basis of whether it is deciduous(primary) or permanent(secondary), the type of tooth (incisors, cannines)and its proximity to the midline or front of the mouth(medial or lateral). Children have 20 deciduous teeth and have 32 permanent teeth.The type of teeth are identified by their characteristics:-eg.incissors have thin cutting edges ,canines have single prominent cones, premolars have bicuspids,molars have 3 or more cusps.

Parts and structure of the teeth
A tooth has a crown ,neck, and root. The crown projects from gingiva. The neck is between the crown and the root. The root is fixed in the socket by the periodontium. Most of the tooth is composed of dentin , which is covered by enamel ,over the crown and cement over the root.The pulp cavity contains connective tissue, blood vessels and nerves. The root canal transmits the nerves and vessels to and from the pulp cavity through the apical foramen. The tooth sockets are in the alveolar processes of the maxillae and mandible. Adjacent sockets are separated by inter alveolar septa ,with in the socket , the roots of the teeth with more than one root are separated by inter radicular septa.

The root of the teeth are connected to the bone of the alveolar by a springy suspension forming a special type of fibrous joint called a dento-alveolar syndesmosis or gomphosis. The periodontium is composed of collagenous fibers that extend between the cement of the root and the periosteum of the alveolus.

Vasculature of the teeth
The superior and inferior nalveolar arteries ,branches of the maxillary artery ,supply the maxillary and mandibular teeth respectively. Alveolar veins accompany the arteries. Lymphatic vessels from the teeth and gingivae pass mainly to the submandibular lymph nodes. 

Innervation of the teeth
 The upper teeth are innervated by the superior alveolar nerves from the maxillary nerve . These nerves form a superior dental plexes with in the upper jaw,which sends dental branches to the root of each maxillary tooth. The lower teeth are innervated by the inferior alveolar branch of the mandibular nerve ,the nerve entering the mandibular foramen on the medial surface of the ramus of the mandible. An inferior dental plexes is formed, which sends dental branches to the root of each mandibular tooth.

Applied anatomy

Dental caries
Decay of the hard tissues of a tooth results in the formation of dental caries. Treatment involves  removal of the decayed tissues and restoration of the anatomy of the tooth with a dental material. Neglected dental caries eventually invade and inflame tissues in the pulp cavity . Invasion of the pulp by a deep carious lesion results in infection and irritation of the tissues(pulpitis). Because the pulp cavity is a rigid space, the swollen tissues cause considerable pain (toothache).if untreated ,the small vessels in the root canal may die from the pressure of the swollen tissue and the infected material may pass through the apical canal and foramen in to the periodontal tissues. An infective process develops and spreads through the root canal to the alveolar bone, producing an abscess. Pus from an abscess of a maxillary molar tooth may extend in to the nasal cavity or the maxillary sinus. The roots of the maxillary molar tooth are closely related to the floor of this sinus. As a consequence  infection of the pulp cavity may also cause sinusitis or sinusitis may stimulate nerves entering the teeth and stimulate a toothache.

Extraction of teeth
Impacted third molars become painful ,they have to be removed . when doing this ,caution is taken to avoid injury to lingual nerve as this is closely related to the medial aspect of teeth.   

Salivary glands
The salivary glands are the parotid ,submandibular , and sublingual glands. The clear ,tasteless, odorless viscid fluid , saliva, secreted by these glands and the mucous glands of the oral cavity.

Parotid glands
The parotid gland is the largest of three paired salivary glands. These are situiated one on each side of the face just below the external acoustic meatus. The parotid gland is enclosed with in a tough fascial capsule ,the parotid sheath. Each gland has a parotid duct opening in to the mouth at the level of the second upper molar tooth.

Nerve supply
The glands are supplied by parasympathetic and sympathetic nerve fibers. The parotid plexus of facial nerve(CN VII) is embedded within it, but it does not provide innervation  to the gland . The great auricular nerve, a branch of the cervical plexus composed of fibers from C2 and C3 spinal nerves ,innervates the parotid sheath. The parasympathetic component of the glossopharyngeal nerve (CNIX) supplies presynaptic secreatory fibers to the otic ganglion. The post synaptic parasympathetic fibers are conveyed from the ganglion to the gland by the auriculotemporal nerve.Sympathetic fibers are derived from the cervical ganglia through the external carotid nerve plexes on the external carotid artery. Parasympathetic stimulation increases secretion, where as sympathetic stimulation decreases it. 

Applied anatomy
  1.parotidectomy

About 80% of salivary gland tumors occur in the parotid glands. Most of them are benign, but most salivary gland cancer begins in the parotid gland. Parotidectomy is often the treatment. Because the parotid plexus of facial nerve are embedded in the parotid gland, the plexus and its branches are in jeopardy during surgery. So the important step in Parotidectomy is the identification ,dissection ,isolation , and preservation of the Facial nerve.

       2.infection of the parotid gland

        The parotid gland may become infected by infectious agents that pass through the blood stream, as occurs in mumps. The infection of the gland causes inflammation (parotiditis) and swelling of the gland . Severe pain occurs because the parotid sheath limits swelling. Often the pain is worse during chewing because the enlarged gland is wrapped around the posterior border of the ramus of the mandible and is compressed against the mastoid process of the temporal bone when the mouth is opened. The mumps virus may also cause inflammation of the parotid duct , producing redness of the parotid papillae ,a small projection at the opening of the duct in to the superior oral vestibule. Because the pain produced by the mumps may be confused with a toothache , redness of the papilla is often an early sign that disease involves the gland and not a tooth. Parotid gland disease causes pain in the auricle, external acoustic meatus, temporal region , and TMJ because the auriculotemporal nerve , from which the parotid gland and the sheath receive sensory fibers , also supplies sensory fibers to the skin over the temporal fossa and the mandible.

3. abscess in the parotid gland
A bacterial infection localized in the parotid gland usually produces an abscess. The infection could result from extremely poor hygiene and spread to the gland through the parotid ducts.

4. Sialography of parotid duct
A radiopaque fluid can be injected in to the duct system of the parotid gland through a cannula inserted through the orifice of the parotid duct in the mucous membrane of the cheek. This technique (sialography) is followed by radiography of the gland.

5. Blockage of the parotid duct
The parotid duct may be blocked by a calcified deposit , called a sialolith or calculus. The resulting pain in the parotid gland is worse by eating. Sucking a lemon slice is painful because of the build up of the saliva in the proximal part of the blocked duct.

Submandibular glands
These lie one on each side of the face under the angle of the jaw. The two submandibular ducts open on the floor of the mouth ,one on each side of the frenulum of the tongue.

Sublingual glands
These  glands lie under the mucous membrane of the floor of the mouth in front of the submandibular gland. They have numerous small ducts that open in to the floor of the mouth.

Structure of the salivary gland
The glands are all surrounded by a fibrous capsule. They consists of a number of lobules made up of small acini lined with secretory cells. The secretion is poured  in to ductules which join up to form larger ducts leading in to the mouth.

Nerve suipply
The submandibular gland are supplied by presynaptic parasympathetic secretomotor fibers conveyed from the facial nerve to the lingual nerve by the chorda tympani nerve ,which synapse with the postsynaptic neurons in the submandibular ganglion.The nerves of the sublingual gland accompany the submandibular gland. Presynaptic parasympathetic secretomotor fibers are conveyed by the facial , chorda tympani , and lingual nerves to synapse in the submandibular ganglion. 

Blood supply
The arterial supply of the submandibular gland is from the submental arteries and the sublingual glands is from the sublingual and submental arteries , branches of the lingual and facial arteries respectively.The venous drainage is in to the external jugularveins