Temporomandibular Joint
Gilbert M. Willett
Overview of the Temporomandibular Joint
The temporomandibular joints (TMJs) and related structures play an essential role in mastication (chewing). The act of chewing is resultant from coordinated neuromuscular interaction between cranial nerves of the central nervous system, muscles of mastication, tongue, teeth, and the paired TMJs. The TMJ complex is also involved to some degree in speaking and swallowing.
Anatomy Overview
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The TMJ is classified as a ginglymoarthrodial joint (displays both hinge and sliding capabilities).
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Dental (teeth) occlusion and TMJ positioning (location of the mandibular condyles) are interrelated ().
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A dense fibrous articular disk sits between the bony components of the TMJ. This oval disk is shaped to fit optimally between the mandibular condyle and the articular eminence of the temporal bone.
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The disk is thicker anteriorly and posteriorly, which helps it maintain position over the mandibular condyle.
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Circumferential disk attachment to the surrounding joint capsule creates superior and inferior joint cavities ().
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A retrodiskal tissue (pad) is attached to the posterior aspect of the disk/capsule.
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Medial and lateral aspects of the joint capsule and disk are attached to their respective condyle poles via lateral collateral and medial collateral ligaments.
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Two accessory TMJ ligaments (sphenomandibular and stylomandibular) help suspend the mandible from the skull. They are located medial to the joint and oriented in an anterior and inferior direction from the skull base ().
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A key consideration for mandibular surgery and trauma management: the primary blood supply to the condylar heads of the mandible is the inferior alveolar artery on each side ().
TMJ Sensory (Afferent) Innervation
Hilton’s law is an excellent tool for understanding joint innervation. It states that a joint will receive sensory innervation from the nerves that supply the muscles that cross and act on the joint.
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The primary source for sensory innervation of the TMJ capsule (see ) is branches of the mandibular division of the trigeminal nerve (V3).
TMJ Neuromuscular Control
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Many muscles contribute directly or indirectly to mandibular movement (see ). Those which directly affect mandibular movement are the muscles of mastication (see , , ):
Common Temporomandibular Joint–Related Disorders and Differential Diagnosis Clinical Correlation Examples
Temporomandibular joint–related disorders (TMD) are disorders of the musculoskeletal system and represent the most common cause of chronic pain in the orofacial region. The signs and symptoms of TMD commonly include:
Common TMD Diagnoses
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Myogenous pain: spasm involving one or more of the muscles of mastication. Mandibular opening may or may not be limited.
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Hypermobility: excessive opening of the mandible accompanied by anterior subluxation of the mandibular condyles.
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Inflammation: difficulty identifying the primary tissue involved (e. g., synovitis, capsulitis, retrodiskitis) often results in the label of “arthralgia.”
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Osteoarthritis – signs and symptoms include TMJ-related degeneration, pain, and crepitus.
Trigeminal neuralgia (TN), also known as “tic douloureux,” is a neuropathic pain condition that can be mistaken for a TMJ disorder. TN involves the fifth cranial nerve (trigeminal nerve). This disorder is most commonly characterized by episodes of intense, stabbing pain along the sensory distribution of the trigeminal nerve. It can include any number of the three divisions (ophthalmic, maxillary, and mandibular) of the nerve. It is most commonly unilateral, but can be bilateral. In some cases, TN may also manifest as a less intense, more constant dull aching or burning pain.
Potential causes of TN may include pressure on the nerve (e. g., blood vessel aneurysm or tumor) or possibly due to a neural disease such as multiple sclerosis. Dental care–related trauma to the nerve is another potential source of origin. In some cases, no underlying cause can be identified (idiopathic). The cause of symptom variation (intense stabbing vs. dull ache) is also unknown. TN is managed pharmacologically and/or by surgery or injection of neurotoxic agents.
A maxillary molar infection can result in severe, persistent, throbbing aching in the molar area as well as radiation to the ear, mandible, or neck. Dental caries or bacterial entrapment related, this infection can progress from the space between the tooth and the alveolar bone to abscess formation around the apex region of the involved tooth root. If untreated, the abscess could erode into the surrounding areas (all near the TMJ). Potential routes include the maxillary sinus, nasal cavity, surrounding bone (osteomyelitis), or surrounding soft tissues (cellulitis and facial swelling). Significant problems or even death are likely to occur if the infection spreads into the retropharyngeal, mediastinal, intracranial, or the intraorbital spaces.
The maxillary molars are innervated by the posterior superior alveolar branch of the maxillary division of the trigeminal nerve. Sensory overlap with the primary source of TMJ sensory innervation (auriculotemporal branch of the mandibular division of the trigeminal nerve) is likely in this area. Dental periapical abscess signs and symptoms include fever, tooth pain, facial swelling, dysphagia, trismus, and possibly dyspnea. Radiological imaging is the most common tool used to diagnose this condition. Management includes abscess drainage, root canal or extraction of the involved tooth, and appropriate antibiotic therapy.
Cluster headaches (CH) are an uncommon, severe form of primary neurovascular headaches, diagnostically classified as a trigeminal autonomic cephalgia. Unilateral, severe (searing, burning, and stabbing) headache pain behind or above the eye or at the temple are commonly described symptoms of a CH. In addition, unilateral autonomic signs and symptoms are associated with CH. They are ipsilateral and only occur during the painful stage of a CH; they include ptosis, miosis, lacrimation, conjunctival injection, rhinorrhea, and nasal congestion.
The pathogenesis of CH is complex and has not been fully confirmed. The two most widely accepted theories of pathogenesis are the following: (1) primary CH is characterized by hypothalamic activation with secondary activation of the trigeminal autonomic reflex, probably via a trigeminal-hypothalamic pathway, and (2) neurogenic inflammation of the walls of the cavernous sinus obliterates venous outflow and thus injures the traversing sympathetic fibers of the intracranial internal carotid artery and its branches. For patients with suspected CH, neuroimaging with a cranial computed tomography (CT) scan or a cranial magnetic resonance imaging (MRI) study is recommended to exclude abnormalities of the brain and pituitary gland. Initial treatment recommendations include pharmacological management with triptans or oxygen therapy. There are several promising but unproven neurostimulation-based approaches being used to treat unresponsive CH. However, these interventions remain investigational with unproven long-term benefit and safety.
Questions and Answers
Answer C: The auricular branch of the vagus nerve innervates the concha and most of the area around the auditory meatus. Thus, it should not be affected by TMJ related problems. (A) tinnitus or “ringing” in the ears is a common symptom reported by individuals with TMJ dysfunction; (B) the auriculotemporal branch of V3 innervates this area as well as the TMJ, therefore pain in the TMJ may be referred to this area; (D) swelling is a common sign which occurs in conjunction with TMJ dysfunction.
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Which of the following tissues is not innervated, thus a patient would not feel pain if the tissue was damaged?
Answer A: Only the disc periphery is innervated and vascularized. (B) This area is innervated the auriculotemporal branch of V3 and sensitive to irritation/injury. (C) This area is commonly innervated by V3 and sometimes the great auricular branch of the cervical plexus. (D) The nerve to the lateral pterygoid muscle provides both motor and sensory innervation to the muscle and tendon.
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A teenager fell forward onto a concrete surface making initial contact with his chin. This resulted in a fracture of the neck of the mandibular condyle on one side. Blood supply to the mandibular condyle must remain intact to promote proper healing of the condylar region and prevent subsequent deformity of the condyle due to boney necrosis. Which artery (located in the bone marrow) supplies this area, thus placing it at risk in a fracture such as the one described above?
Answer D: The main source of condylar head vascularization is the inferior alveolar artery. The artery enters the bone at the mandibular foramen and supplies the bone marrow of the whole mandible as well as its cortical layer. This is a key consideration for mandibular surgery and trauma management. (A) This artery may supply the TMJ area, but not condylar head specifically. (B) This artery may supply the TMJ area, but not condylar head specifically. (C) This artery may supply the TMJ area, but not condylar head specifically.
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When you ask your patient to protrude their mandible, their mandible protrudes slightly, but primarily deviates to the left. Injury of which nerve is most likely to cause this?
Answer C: The left lateral pterygoid is not functioning in this example. It is innervated by the left CN V3. (A) Injury to the left facial nerve would not affect mandibular movement, but it would affect the muscles of facial expression on the left side of the face. (B) The ansa cervicalis does not innervate any of the muscles of mastication, but does innervate some muscles that assist with mandibular movement—however damage to this nerve would not significantly affect mandibular protrusion. (D) Injury to the right CN V3 would affect function of the R lateral pterygoid muscle. This loss would result in mandibular movement towards the right when protrusion is attempted.
Salivary Glands
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Describe the function of the structural components associated with major and minor salivary glands.
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Explain the function of saliva and the mechanism of production.
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Explain how alterations in flow rate may impact the composition of saliva and the physiological significance of a low flow rate.
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Explain the neural mediated reflex pathway that controls stimulated salivary secretion.
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Describe the types of afferent stimuli involved in eliciting salivation. Include the types of sensory receptors and the afferent path followed.
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Describe the efferent outflow path for the major salivary glands. Include both parasympathetic and sympathetic fibers.
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Explain how medications may affect the efferent signaling pathway and alter secretion.
Overview of the Salivary Glands
Salivary glands associated with the oral cavity produce a complex, slightly alkaline watery secretion that contains various proteins, ions, and enzymes. Salivary secretion occurs continuously, at low levels, with intermittent increases occurring in response to eating and oral stimulation through autonomic innervation. The composition and continual secretion of saliva function to maintain oral cavity homeostasis. Saliva serves to cleanse and protect the oral mucosa, provide antimicrobial protection, maintain a neutral pH, and preserve tooth integrity. The lubrication and moisture produced by saliva facilitates speaking and mediates digestive functions, including the process of chewing, taste, bolus formation, and swallowing. Salivary gland dysfunction has a significant impact on oral health and quality of life. This chapter discusses the anatomical structure, location, and neural mechanisms that control the secretion of the major and minor salivary glands.
General Development of Salivary Glands
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Salivary glands develop concomitantly with the formation of the orofacial complex during the 6 to 12 weeks of embryonic development and arise from the oral epithelium.
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Each gland undergoes extensive branching within the underlying connective tissue to form clusters of salivary secretory cells, known as acinar units, and excretory ducts, which open onto the epithelial surface to release saliva into the oral cavity.
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Secretory acinar units function to produce saliva and may consist of two types of secretory acinar cells: serous and mucous cells.
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Salivary glands may contain just serous cells, only mucous cells, or both. The predominant type of acinar unit present in a gland defines the type of saliva produced. Glands that contain predominantly serous cells produce a thin watery enzyme-rich secretion, whereas glands comprised mainly of mucous cells secrete a thick, viscous, mucin-rich secretion.
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The duct system serves to collect and then modify the ionic composition of the saliva produced by the secretory acinar cells. The smaller collecting ducts found within the gland eventually coalesce to form larger excretory ducts that transport saliva to the oral mucosal surface.
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Gland Classification
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Salivary glands are primarily classified into two groups based on size and location, as major and minor salivary glands. Alternatively, salivary gland classification may be based on the type of saliva produced and include serous glands, mucous glands, and seromucous (mixed) glands ().
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Major salivary glands include the parotid, submandibular, and sublingual glands.
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The three major salivary glands are large, bilateral, paired structures that reside outside the oral cavity (extraoral) and empty salivary secretions into the oral cavity via long excretory ducts. The excretory ducts open onto either side of the dental arch and serve to saturate the food bolus with saliva during chewing.
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The three major salivary glands collectively produce 90% of the total salivary output.
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Minor salivary glands, which are named based on their anatomical location within the oral cavity, include labial, buccal, lingual, palatal, and pharyngeal glands.
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Fig. 24.1 Location of the three major salivary glands. Right lateral view: mandible and mylohyoid removed. The parotid, submandibular, and sublingual gland represent the major salivary glands and produce 90% of the total salivary output. The major glands are bilateral paired structures, located outside the oral cavity proper. Each gland empties into the oral cavity via a long excretory duct.
Anatomical Overview of Major and Minor Salivary Glands
Parotid Glands
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The paired parotid glands, which are the largest of the three major glands consist of serous acinar cells, and produce a thin, low-viscosity, enzyme-rich secretion ( ).
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Each parotid gland resides in a triangular space, the parotid fossa, in the preauricular region, just anterior to the ear and along the posterior border of the mandibular ramus.
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The stylomandibular ligament and facial nerve (CN VII) pass through the parotid gland, dividing each gland into a superficial lobe and a deep lobe.
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The large excretory duct of the parotid gland, known as Stensen’s (parotid) duct, emerges from the deep lobe along the anterior border of the parotid gland, crosses the masseter muscle, and pierces the buccinator muscle to enter the oral cavity.
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Nerve structures anatomically associated with the parotid gland include the facial nerve (CN VII), greater auricular nerves (C2–C3), and auriculotemporal nerves (CN V3).
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The facial nerve (CN VII), which passes through the parotid gland, does not provide innervation to the gland.
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The motor (SVE) division of the facial nerve exits the base of the skull and immediately gives rise to three branches that innervate the stylohyoid, posterior digastric, and auricularis muscles.
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The facial nerve enters the gland, bifurcates into two main trunks, and then divides into five terminal branches to form the parotid nerve plexus. The five terminal branches of the plexus include the temporal, zygomatic, buccal, marginal mandibular, and cervical nerve branches, which innervate the muscles of facial expression.
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The greater auricular nerve, which originates from C2–C3 of the cervical plexus, and the auriculotemporal branch of V3 nerve, both transmit general sensation (general somatic afferent [GSA] fiber) from the region of the skin covering the parotid gland.
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Secretomotor (general visceral efferent [GVE] fiber) innervation originates from both parasympathetic and sympathetic divisions. The parotid glands produce approximately 25% of total salivary output under unstimulated (basal) conditions. However, during autonomic stimulation, the parotid secretes 60% of the total salivary flow.
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Parasympathetic innervation arises from the inferior salivatory nuclei and travels to the parotid gland via the tympanic branch of CN IX and the lesser petrosal nerve (CN IX). Postganglionic fibers originate from the otic ganglion and accompany the auriculotemporal branch (V3) for secretomotor distribution to the parotid gland.
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Sympathetic innervation arises from neurons in the lateral horn of the thoracic spinal (T1–T4) cord and synapse in the superior cervical ganglion. Postganglionic fibers follow the vascular supply.
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Fig. 24.2 Left lateral view of the anatomical location of the parotid gland in the parotid fossa. (a) The parotid gland, which consists of a superficial and deep lobe, sits anterior to the ear and along the posterior border of the mandibular ramus. The parotid duct arises from the deep lobe, crosses the face superficial to the masseter muscle, and pierces the buccinator to enter the oral cavity. The parotid duct opens into the buccal vestibule of the mouth opposite the second maxillary molar. The parotid produces a pure serous, watery secretion. (b) Magnified image of the parotid gland demonstrating the position of the facial nerve. The facial nerve passes through the parotid gland, splitting the gland into a superficial lobe and a deep lobe, but does provide innervation to the gland. The facial nerve emerges from the stylomastoid foramen, enters the parotid gland, and divides into five terminal branches, to form the parotid nerve plexus. (c) Schematic of the terminal motor branches of the facial nerve. (a,b: Reproduced with permission from Gilroy AM, MacPherson BR. Atlas of Anatomy. Third Edition. © Thieme 2016. Illustrations by Markus Voll and Karl Wesker. c: Reproduced with permission from Baker EW. Anatomy for Dental Medicine. Second Edition. © Thieme 2015. Illustrations by Markus Voll and Karl Wesker.)
Frey’s syndrome is a relatively rare disorder associated with gustatory sweating, which occurs shortly after eliciting a salivary reflex in response to chewing. It is characterized by unilateral flushing and sweating of the skin in the region supplied by the auriculotemporal nerve. The segmental distribution pattern of innervation includes the frontotemporal region (forehead), check, anterior ear, and parotid region. Frey’s syndrome occurs most often following parotid surgery and is presumably associated with damage to the GSA and GVE fibers associated with the auriculotemporal nerve. It is predicted that following surgery, the GVE parasympathetic fibers join the sympathetic fibers as the auriculotemporal nerve fibers regenerate. The intermingling of fibers results in flushing and sweating during salivation due to sympathetic innervation.
Neoplasms arising in the parotid gland, which may be benign (80%) or malignant (20%), occur in the superficial or deep lobe, respectively. A key consideration for any parotidectomy is the isolation of the facial nerve at the level of the main trunk as it exits the stylomastoid foramen. Benign tumors are most often associated with the superficial lobe and removed through a superficial parotidectomy. Tumors occurring in the deep lobe must be resected from the stylomandibular ligament, which separates the superficial and deep lobes. Deep parotid tumors may push the facial nerve (CN VII) superficially and increase the risk of injury.
Parotitis refers to inflammation of the parotid gland or duct that may be caused by bacterial or viral infections. Other diseases associated with inflammation such as the mumps, tuberculosis, the autoimmune disease, Sjogren’s syndrome, or the human immunodeficiency virus (HIV) may also cause parotitis. Inflammation of the gland leads to decreased salivary flow and, in some cases, scarring and obstruction of the ducts, which allow for bacteria and viruses to infect the secretory portions of the gland. Clinical manifestations include localized ear pain, tenderness anterior to the ear, and difficulty or pain with chewing and swallowing. Neurological complications are rare but may include meningitis (inflammation of meninges), deafness, and facial nerve inflammation (facial neuritis).
Submandibular Glands
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The paired submandibular glands, which are smaller than the parotid, are mixed salivary glands containing primarily serous cells with some mucous acinar cells.
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Each submandibular gland sits just below the angle of the mandible, in the submandibular (digastric) triangle, an anatomic region formed by the anterior and posterior digastric muscles and the inferior border of the mandible. The submandibular gland creates a C-shaped ring around the posterolateral edge of the mylohyoid muscle to form a superficial lobe and a deep lobe ().
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The main excretory duct of the submandibular gland, known as Wharton’s duct, exits the medial side of the gland and passes between the hyoglossus and mylohyoid muscles to enter the floor of the oral cavity.
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The submandibular duct exhibits a long, convoluted path in comparison to the ducts of other major glands. The long route may serve as a contributing factor to the formation of salivary calculus (sialolithiasis) and lead to the obstruction of saliva released into the oral cavity.
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Each duct empties just lateral to the midline, behind the mandibular incisors at the sublingual papillae (caruncle), which is near the base of the lingual frenulum ().
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Nerve structures associated with the submandibular gland include the marginal mandibular branch of VII, the lingual nerve (CN V3), and the hypoglossal nerve (CN XII).
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The lingual nerve, a branch of the mandibular (V3) division of the trigeminal, enters the posterior portion of the oral cavity through the infratemporal fossa and travels with the chorda tympani (VII) along the floor of the oral cavity.
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The submandibular parasympathetic ganglion lies on the lateral surface of the hyoglossus muscle, near the deep lobe of the submandibular gland, and attaches to the lingual nerve. The ganglion serves as the synaptic connection for the preganglionic (GVE) fibers of the chorda tympani nerve ().
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The lingual nerve crosses the submandibular (Wharton’s) duct passing from the lateral side, inferiorly, and then medial to the submandibular duct, to supply GSA fibers to the oral mucosa and submandibular glands ( and ).
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The hypoglossal nerve (CN XII) enters the posterior portion of the oral cavity through the submandibular triangle and runs inferior to Wharton’s duct, the submandibular gland, and the lingual nerve. The hypoglossal nerve does not innervate the submandibular gland; it provides GSE fibers to all intrinsic and extrinsic muscles of the tongue, except for the palatoglossus muscle ().
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The submandibular gland, which produces approximately 50% of the total salivary output during resting conditions, receives neural stimulation from both parasympathetic and sympathetic innervation. During autonomic stimulation, salivary secretions constitute only 30% of the total salivary output.
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Parasympathetic (GVE) innervation originates from the superior salivatory nuclei and travels to the submandibular gland via the chorda tympani branch of the facial nerve (CN VII). Postganglionic (GVE) fibers arise from the submandibular ganglion and continue to travel with the lingual nerve (V3) for secretomotor distribution to the submandibular and sublingual glands.
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Sympathetic innervation arises as preganglionic fibers from the intermediolateral cell column (IMLC) of the spinal cord (T1–T4), which then synapse in the superior cervical ganglion of the sympathetic trunk. Postganglionic fibers follow the vascular supply to reach the gland.
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Fig. 24.3 Anatomical location of the submandibular and sublingual glands in the floor of the mouth. Superior view of the floor of the oral cavity, with the tongue removed. The submandibular glands are mixed salivary glands producing both mucous and serous secretions. The glands sit below the angle of the mandible in the floor of the oral cavity. The glands wrap as a C-shaped ring around the posterolateral edge of the mylohyoid to form a superficial lope and a deep lobe. The submandibular duct (Wharton’s duct) emerges from the medial surface of the gland, crosses over the lingual nerve, and passes anteriorly to open on to the sublingual papilla. Note the submandibular duct cross over the lingual nerve. the sublingual glands are predominantly mucous-secreting salivary glands, located anteriorly in the floor of the oral cavity, between the oral mucosa and the mylohyoid muscle. The sublingual gland drains through several smaller excretory ducts that open on the sublingual fold. Alternatively, the sublingual glands may have a main duct that opens into the submandibular duct at the sublingual papillae. (Reproduced with permission from Baker EW. Anatomy for Dental Medicine. Second Edition. © Thieme 2015. Illustrations by Markus Voll and Karl Wesker.)
Fig. 24.4 The location of the submandibular parasympathetic ganglion in the submandibular triangle. Right lateral view of the medial surface of the mandible, with the medial pterygoid muscle cut. The ganglion is suspended inferiorly from the lingual nerve and lies on the lateral surface of the hyoglossus muscle, near the deep lobe of the submandibular gland. The preganglionic parasympathetic fibers from the superior salivatory nucleus in the central nervous system (CNS) accompany the nervus intermedius and the chorda tympani nerve (CN VII). The chorda tympani nerve joins the pathway of the lingual nerve in the infratemporal fossa and travels with the lingual nerve to reach the submandibular ganglion. Postganglionic secretomotor fibers pass to the submandibular, sublingual, and minor lingual and labial glands in the anterior floor of the mouth and lower lip. (Modified with permission from Gilroy AM, MacPherson BR. Atlas of Anatomy. Third Edition. © Thieme 2016. Illustrations by Markus Voll and Karl Wesker.)
Fig. 24.5 Left lateral view of the anatomical relationship between the submandibular duct, submandibular ganglion, hypoglossal nerve, and lingual nerve, with the submandibular gland and the mylohyoid muscle removed. The lingual nerve and the submandibular ganglion lie on the lateral surface of the hyoglossus muscle, near the deep lobe of the submandibular ganglion. The duct runs superior to the hypoglossal nerve (CN XII) and inferior to the lingual nerve as it passes between the hyoglossus and mylohyoid muscle. The lingual nerve crosses the duct laterally at the anterior border of the hyoglossus muscle, and then loops beneath the submandibular duct, and continues medially to the duct as the nerve passes anteriorly toward the tip of the tongue. The hypoglossal nerve (CN XII) lies inferior and deep to the submandibular gland and passes superficial to the hyoglossus muscle. (Modified with permission from Gilroy AM, MacPherson BR. Atlas of Anatomy. Third Edition. © Thieme 2016. Illustrations by Markus Voll and Karl Wesker.)
Salivary gland inflammation, known as sialadenitis, may be associated with pain, tenderness, redness, and swelling in the region of the gland. Bacterial and viral infections of the parotid or submandibular gland are often associated with acute onset of sialadenitis. In cases of infection, fever, malaise, and inflammation of the ductal papillae are often associated with symptoms. Chronic and recurring forms of sialadenitis also exist. Obstruction due to salivary calculi (sialoliths) or stricture in the duct often leads to pain, inflammation, and swelling. Obstructive sialadenitis due to a sialolith is referred to as sialolithiasis and most often occurs in the submandibular duct (Wharton’s duct). The increased incidence of sialoliths in Wharton’s duct is attributed to the length, position, and path of the duct. Patients often complain of tenderness, sudden swelling, and increased pain that is associated with salivation during eating. Dehydration, anticholinergics, and conditions related to xerostomia (dry mouth), including the autoimmune disease, Sjogren’s disease, may increase the incidence of sialolithiasis (stone formation) and possible infection due to decreased salivary flow. Long-term complications of chronic sialadenitis and untreated sialolithiasis can lead to scarring and glandular atrophy.
Based on the anatomical relationship of the submandibular duct and submandibular gland to the vessels and nerves that pass through the submandibular triangle, several structures should be considered during the excision of the submandibular gland, or during the removal of salivary duct stones. The superficially located marginal mandibular and cervical branches of VII, as well as the medially positioned hypoglossal nerve (CN XII), and the lingual nerve (CN V3), should be considered during the excision of the submandibular gland, or during the removal of salivary duct stones. The facial artery passes deep to the gland, whereas the facial vein lies superficially. Among structures at risk, the marginal mandibular branch (VII) is the most likely structure damaged or bruised during submandibular gland removal. However, the hypoglossal and lingual nerves, along with the secretomotor fibers carried by the chorda tympani nerve, are also potentially at risk. During surgery, the submandibular duct should also be identified and dissected to avoid damage to the lingual nerve, or the submandibular ganglion.
Sublingual Glands
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The paired sublingual glands (), which are the smallest of the three major salivary glands, lack a definitive connective capsule and lie below the oral mucosa, anteriorly in the region of the floor of the oral cavity.
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The sublingual glands are mixed, consisting mainly of mucous acinar cells with only a few serous cells.
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The sublingual glands, which contribute only 5 to 10% of the total salivary output during resting conditions, receive neural stimulation from both parasympathetic and sympathetic innervation.
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The main duct, Bartholin’s duct, opens into the submandibular duct at the sublingual papillae (caruncle).
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Several small sublingual ducts, also known as the ducts of Rivinus, may also be present and open along the sublingual fold on the floor of the oral cavity.
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Both the sublingual glands and the minor salivary glands exhibit a limited excretory duct system, with striated ducts often absent. The short ducts reduce the occurrence of salivary duct stone formation.
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Fig. 24.6 Sublingual gland and sublingual papilla. Anterior view showing the ventral surface of the tongue (superficial and deep views). The paired sublingual glands lie below the oral mucosa in the floor of the oral cavity. The main duct (Bartholin’s duct) empties into sublingual papilla. (Reproduced with permission from Baker EW. Anatomy for Dental Medicine. Second Edition. © Thieme 2015. Illustrations by Markus Voll and Karl Wesker.)
Minor Salivary Glands
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Approximately 600 to 1,000 minor salivary glands reside in the submucosal connective tissue within the oral cavity and the oropharynx ().
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The glands are nonencapsulated, consisting of small aggregates of mucous and serous acinar cells, which produce approximately 5 to 10% of total salivary output (see and ).
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Minor glands secrete saliva continuously through constitutive exocytosis; however, feedback from the parasympathetic and sympathetic system, as well as physiological and pharmacological input, may modify secretory activity.
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Secretomotor fibers that innervate the minor glands follow preganglionic fibers of the glossopharyngeal or facial nerves. Postganglionic fibers are distributed through branches of CNs V2 and V3.
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Most of the saliva (70%) secreted from the minor glands is a thick, viscous, mucin-rich secretion that is essential for the lubrication and hydration of the oral mucosa in the palatal, oropharyngeal, labial and buccal regions.
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Minor glands that contain primarily mucous cells are found in the submucosa of the oropharyngeal isthmus, the posterior hard and soft palates, and the posterior one-third of the tongue.
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Minor mixed glands reside in the tip of the anterior tongue and the labial and buccal regions.
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Minor glands containing only serous acinar cells are situated anterior to the sulcus terminalis in association with taste buds of the circumvallate and foliate papillae.
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The duct system in minor glands is less extensive than the major glands. Small collecting ducts serve to release unmodified, isotonic saliva constitutively onto the mucosal lining of the oral cavity.
Fig. 24.7 (a,b) Schematic depiction of the location of types of minor salivary glands. In addition to three paired glands, 600 to 1,000 minor salivary glands secrete pure mucous, pure serous, or a mixed salivary secretion into the oral cavity. Minor glands only produce 5 to 8% of the total saliva output, but this amount suffices to keep the oral cavity lubricated when the major glands are at rest. (Modified with permission from Baker EW. Anatomy for Dental Medicine. Second Edition. © Thieme 2015. Illustrations by Markus Voll and Karl Wesker.)
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