Muscles of Mastication PDF

Muscles of Mastication are related to the jaws and are responsible for the masticatory function and speech.  Muscles of Mastication 1. Masseter 2. Medial pterygoid 3. Lateral pterygoid 4. Temporalis  Masseter muscle is a quadrilateral-shaped muscle located...

Muscles of Mastication are related to the jaws and are responsible for the masticatory function and speech.  Muscles of Mastication 1. Masseter 2. Medial pterygoid 3. Lateral pterygoid 4. Temporalis  Masseter muscle is a quadrilateral-shaped muscle located on the lateral surface of ramus of mandible and originates as three different layers: 1. Superficial layer: It is the biggest layer and originates from the anterior two-third of the lower border of the zygomatic arch and the adjacent zygomatic process of maxilla. It runs downwards and posteriorly at 45° into the lower lateral surface of the mandibular ramus. 2. Middle layer: It begins from the deeper surface of the anterior two-third of the zygomatic arch and the posterior one-third. These run vertically downwards to become inserted into the middle part of the ramus. 3. Deep layer: It originates from the deep surface of the zygomatic arch, descends vertically and inserts into the upper part of the ramus and the coronoid process. Masseter muscle  Medial Pterygoid has a superficial and a deep head. ❏ The superficial head - is small and arises from the maxillary tuberosity. ❏ The deep head - is large and arises from the medial surface of the lateral pterygoid plate and the adjoining process of the palatine bone. All the fibres are inserted into a roughened area on the medial surface of the mandibular angle and the ramus.bone. All the fibres are inserted into a roughened area on the medial surface of the mandibular angle and the ramus. Medial Pterygoid  Lateral Pterygoid has two heads: ❏ Upper head- This arises from the infratemporal surface and the crest of the greater wing of the sphenoid. ❏ Lower head- This arises from the lateral surface of the lateral pterygoid plate. The fibres of both the heads converge and become inserted into the pterygoid fovea present at the neck of the mandible and the anterior margin of the articular disc and capsule of the temporomandibular joint (TMJ). Lateral Pterygoid  Temporalis The origin of this fan-shaped muscle is the temporal fossa and the temporal fascia. Fibres pass deep to the zygomatic arch and insert into the coronoid process and the anterior border of the ramus. Temporalis  Innervation and Blood Supply Motor: Motor supply is provided by the muscular branches of the mandibular nerve (V3 of the trigeminal nerve). Sensory: Sensory supply is by the trigeminal nerve. Vascularity: The vascularity of the muscles of mastication is maintained by the second part of the maxillary artery. Myofascial Pain Dysfunction Syndrome (MPDS) - It involves pain originating from the muscles of mastication, their sheaths, tendons or ligaments. Pain is referred to the face, head and neck regions. - The common causes are improper dental occlusion and nocturnal bruxism. - Treatment includes analgesics and muscle relaxants What is the role of salivary glands The main salivary gland function is saliva production. Saliva plays an important role in supporting your oral and overall health. For example, saliva: Keeps your mouth and throat lubricated and comfortable. Moistens food so it’s easier to swallow. Contains an enzyme called amylase, which helps your stomach break down starches in food. Keeps your mouth clean. Helps reduce your risk of cavities and gum disease. Helps maintain the pH balance in your mouth.  The Parotid Gland is a bilateral structure, which displays a lobular and irregular morphology. It lies within a deep hollow, known as the parotid region The parotid region is bounded as follows: Superiorly – Zygomatic arch. Inferiorly – Inferior border of the mandible. Anteriorly – Masseter muscle. Posteriorly – External ear and sternocleidomastoid.  The Parotid Gland The secretions of the parotid gland are transported to the oral cavity by the Stensen duct. It arises from the anterior surface of the gland, traversing the masseter muscle. The duct then pierces the buccinator, moving medially. It opens out into the oral cavity near the second upper molar. Vasculature Blood is supplied by the posterior auricular and superficial temporal arteries. Venous drainage is achieved via the retromandibular vein. Innervation The parotid gland receives sensory and autonomic innervation. The autonomic innervation controls the rate of saliva production. Sensory innervation is supplied by the auriculotemporal nerve (gland) and the great auricular nerve (fascia). Parotid Gland Tumours The parotid gland is the most common site of a salivary gland tumour. These tumours are usually benign, such as an adenolymphoma. Parotitis inflammation of the parotid gland, usually as a result of an infection. The parotid gland is enclosed in a tough fibrous capsule. This restricts swelling of the gland, producing pain.  The Sublingual Gland the smallest of the three paired salivary glands. almond-shaped and lie on the floor of the oral cavity. They are situated underneath the tongue, bordered laterally by the mandible and medially by genioglossus muscle of the tongue. The glands form a shallow groove on the medial surface of the mandible known as the sublingual fossa. Both glands contribute to only 3-5% of overall salivary volume, producing mixed secretions which are predominantly mucous in nature. These secretions are important in lubricating food, keeping the oral mucosa moist and initial digestion. The Sublingual Gland  The Sublingual Gland submandibular duct and lingual nerve pass alongside the medial aspect of the sublingual gland. Both sublingual glands unite anteriorly and form a single mass through a horseshoe configuration around the lingual frenulum. The superior aspect of this U-shape forms an elevated, elongate crest of mucous membrane called the sublingual fold (plica sublingualis). Each sublingual fold extends from a posterolateral position and traverses anteriorly to join the sublingual papillae at the midline, either side of the lingual frenulum. Secretions drain into the oral cavity by minor sublingual ducts (of Rivinus), of which there are 8-20 excretory ducts per gland, each opening out onto the sublingual folds. Vasculature Blood supply is via the sublingual and submental arteries Venous drainage is through the sublingual and submental veins Innervation receive autonomic innervation through parasympathetic and sympathetic fibres, which directly and indirectly regulate salivary secretions respectively. Receive their parasympathetic input via chorda tympani nerve Ranula- - is a type of mucocele (mucous cyst) that occurs in the floor of the mouth inferior to the tongue. It is the most common disorder associated with the sublingual glands due to their higher mucin content in secretions compared to other salivary glands.  The Submandibular Gland are a pair of elongate, flattened hooks which have two sets of arms; superficial and deep. The positioning of these arms is in relation to the mylohyoid muscle, which the gland hooks around. ❏ Superficial arm – comprises the greater portion of the gland and lies partially inferior to the posterior half of the mandible, within an impression on its medial aspect (the submandibular fossa). ❏ Deep arm – hooks around the posterior margin of mylohyoid through a triangular aperture to enter the oral cavity proper. It lies on the lateral surface of the hyoglossus, lateral to the root of the tongue.  The Submandibular Gland The submandibular gland is located within the anterior part of the submandibular triangle. The boundaries of this triangle are: Superiorly: Inferior body of the mandible. Anteriorly: Anterior belly of the digastric muscle. Posteriorly: Posterior belly of the digastric muscle. Secretions from the submandibular glands travel into the oral cavity via the submandibular duct (Wharton’s duct). Vasculature The submandibular gland is supplied by the submental artery and sublingual artery Its venous drainage is by two vessels: Facial vein – empties directly into the internal jugular vein. Sublingual vein – drains into the lingual vein and then internal jugular vein. Parasympathetic Parasympathetic innervation originates from the superior salivatory nucleus Sympathetic Sympathetic innervation originates from the superior cervical ganglion Salivary Duct Calculi - A calculus or sialolith is a calcified deposit which can block the lumen of a duct. The submandibular duct is the most susceptible to calculi out of all the salivary ducts; accounting for approximately 80% of cases. This is thought to be due to the ❏ Torturous length of the duct (5cm) ❏ Ascending secretory pathway ❏ Nature of salivary secretion