Mandible and Muscles of Mastication PDF

THE MANDIBLE Department of Clinical Anatomy School of Laboratory Medicine & Medical Sciences College of Health Sciences University of KwaZulu-Natal V. Bisetty (2024) UKZN INSPIRING GREATNESS  INTRODUCTION Mandible loc...

THE MANDIBLE Department of Clinical Anatomy School of Laboratory Medicine & Medical Sciences College of Health Sciences University of KwaZulu-Natal V. Bisetty (2024) UKZN INSPIRING GREATNESS  INTRODUCTION Mandible located inferiorly in facial skeleton Largest and strongest bone of face Forms lower jaw and contains lower teeth Articulates on either side with temporal bone → temporomandibular joint  OSSIFICATION Begins at about 6 weeks of intrauterine life Via membranous ossification on outer side of Meckel’s cartilage Meckel’s cartilage inferior to incisor teeth forms mandible Accessory pieces of cartilage found in: Coronoid process Condyloid process Mental symphysis These are absorbed eventually At birth → two symmetrical halves united by fibrous tissue at mental symphysis Union is complete at 1 year  ANATOMY Consists of a horizontal body (anteriorly) and two vertical rami (posteriorly) Body and rami meet on each side at angle of mandible RAMUS BODY  BODY Has external and internal surfaces Has upper and lower borders External surface: Mental symphysis (union point) Mental foramen (mental nerve and vessels) Mental protuberance (Triangular elevation) Mental tubercle Orbicularis oris  BODY Lower border: Base Oblique line (continuous with anterior border) Muscle attachments (see diagram) Upper border: Alveolar part Buccinator attachment (posteriorly)  BODY Internal surface: Divided into upper and lower parts by mylohyoid line (for mylohyoid muscle) Superior constrictor of pharynx Digastric fossa Mental spine Genial tubercles Genioglossus (upper two) Geniohyoid (lower two) Sublingual fossa Submandibular fossa  RAMUS Quadrilateral in shape Has external and internal surfaces Has anterior, posterior, superior and inferior borders (Head)  RAMUS External surface: Flat Attachment: Masseter muscle Anterior to this: facial artery Parotid gland (above and behind)  RAMUS Internal surface: Rough Mandibular foramen to canal Inferior alveolar nerve Lingula (sphenomandibular ligament) Attachments: Temporalis; lateral & medial pterygoid muscles  RAMUS Superior border: Posteriorly: Condyloid process Forms head (articulates with mandibular fossa) Neck below head (lateral pterygoid muscle) Capsule of TMJ Lateral ligament of TMJ on lateral side Anteriorly: Coronoid process Flat and triangular *Mandibular notch (masseteric vessels and nerves) between these processes  RAMUS Inferior border: Continuous with inferior border of body Forms angle of mandible Stylomandibular ligament attaches Anterior border: Forms anterior border of coronoid process Temporalis attached Posterior border: In contact with parotid gland MUSCLES OF MASTICATION Department of Clinical Anatomy School of Laboratory Medicine & Medical Sciences College of Health Sciences University of KwaZulu-Natal V. Bisetty (2024) UKZN INSPIRING GREATNESS  MASTICATION Definition: Physical process of chewing food in preparation for swallowing & ultimately digestion. Four pairs of muscles make chewing possible Grouped into 2 different functions FIRST GROUP 3 pairs elevating mandible to close mouth SECOND GROUP 1 pair of muscle working to depress mandible (open jaw), translate jaw from side to side; protrude mandible forward MUSCLES INVOLVED  TEMPORALIS Large, fan-shaped Powerful elevator of mandible Origin Floor of temporal fossa Deep surface of temporal fascia Insertion Coronoid process Anterior border of ramus up to last molar Innervation Deep temporal branches of anterior trunk of mandibular nerve Action Elevates mandible-closing jaws Retraction mandible after protrusion (Posterior fibres)  MASSETER Powerful masticator Quadrangular in shape 2 parts: Superficial and deep Superficial Origin Maxillary process of zygomatic & ant. 2/3rds of zygomatic process Insertion Angle of mandible & lateral surface of ramus Deep Origin Medial surface of zygomatic arch & post. part of inferior margin Insertion Central & upper part of ramus as high as coronoid process  MASSETER Innervation Masseteric branch of mandibular nerve (anterior trunk) B/S Masseteric artery of maxillary artery Action Elevates mandible  LATERAL PTERYGOID Thick, triangular Origin Upper head: Roof of infratemporal fossa Lower head (larger): Lateral surface of lateral pterygoid plate Insertion Capsule of temporomandibular joint Pterygoid fovea Innervation Nerve to lateral pterygoid from anterior trunk of mandibular nerve Action Acting together – protrusion of mandible Side-to-side movements of mandible  MEDIAL PTERYGOID Quadrangular with superficial and deep heads Origin Deep head - medial surface of lateral pterygoid plate; pyramidal process of palatine bone Superficial head - tuberosity of maxilla Insertion Medial surface of ramus of mandible Innervation Nerve to medial pterygoid from main trunk of mandibular nerve Actions Elevates mandible-closes jaw Acting alone protrudes side of jaw Assists lateral pterygoid muscle in protrusion MUSCLES OF MASTICATION MUSCLES OF MASTICATION