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THE MANDIBLE OSTEOLOGY DR. MUHAMMAD MUSTAFA DPT,KMU MANDIBLE The mandible or lower jaw is the largest and strongest bone of the face. it articulates with the skull at the temporo- mandibular joint. Horse shoe shaped body which lodges the teeth . A pair of rami which projects upward from the posterior ends . The body of the mandible meets the ramus on each side at the angle of the mandible THE BODY Each half of the body has outer and inner surfaces and upper and lower borders Outer surface: 1) the symphysis menti is the line at which the right and left halves meet each other. It is marked by a faint ridge. 2) the mental protuberance (chin) is a median triangular projection area in the lower part of the midline. The inferiolateral angles of the protrubrence form the mental tubercles. 3The mental foramen can be seen below the second premolar tooth; it transmits the terminal branches of the inferior alveolar nerve and vessels. 4) the oblique line is the continuation of the sharp anterior border of the ramus of the mandible It runs downward and forward towards the mental tubercle 5) incissive fossa is a depression that lies just below the incisor teeth. SYMPHISIS MENTI The upper border of the body of the mandible is called the alveolar part; in the adult, it contains 16 sockets for the roots of the teeth. The lower border of the body of the mandible is called the base. INCISSIVE FOSSA MENTAL TUBERCLE The inner surface: The mylohyoid line can be seen as an oblique ridge that runs backward and laterally from the area of the mental spines to an area below and behind the third molar tooth . 2) below the mylohyoid line the surface is slightly hollowed out to form the submandibular fossa,which lodges the superficial part of the submandibular gland. 3) above the anterior part of mylohyoid line there is the sublingual fossa in which the sublingual glands lie . 4) the posterior surface of the symphysis menti is marked by 4 small elevations called the superior and inferior genial tubercles 5) the mylohyoid groove(present on the ramus) extends onto the body below the posterior end of the mylohyoid line. The upper or alveolar border bears sockets for the teeth. The lower border is called the base. near the midline the base shows an oval depression called the diagastric fossa. THE RAMUS Its quadrilateral in shape and has two surfaces Lateral Medial It has four borders Upper and lower Anterior and posterior. Coronoid and condyloid process The lateral surface is flat and bears a number of oblique ridges. Medial surface 1)Mandibular foramen lies a little above the centre of the ramus .it leads into the madibular canal which descends into the body of the mandible and opens at the mental foramen 2)The anterior margin of the mandibular foramen is marked by a sharp tongue shaped projection called the lingula. The lingula is directed towards the head of the mandible. 3) the mylohyoid groove begins just below the mandibular foramen,and runs downwards and forwards to be gradually lost over the submandibular fossa The upper border of the ramus is thin and is curved downwards forming the mandibular notch . The lower border is the backward continuation of the base of the mandible. Posteriorly it ends by becoming continous with the posterior border at angle of the mandible The anterior border is thin while the posterior border is thick The condyloid process is flattened triangular upwarsd projection from the posterosuperior part of the ramus . Its upper end is expanded from side to side to form the head. The head is covered with fibrocartilage and articulates with the temopral bone to form the temporomandibular joint . below the head is the neck.its anterior surface presents a depression called the pterygoid fovea. FORAMINA AND RELATIONS TO NERVES AND VESSELS 1) the mental foramen transmits mental nerve and vessels. 2) inferior alveolar nerve and vessels enter the mandibular canal through the mandibular foramen ,and runs forwards within the canal. 3) the mylohyoid nerves and vessels lie in the mylohyoid groove. 4) the lingual nerve is related to the medial surface of the ramus in front of the mylohyoid groove. 5) the area above and behind the mandibular foramen is related to the inferior alveolar nerve and vessels and to the maxillary artery 6) the masseteric nerve and vessels pass through the mandibular notch 7) the auriculotemporal nerve is related to the medial side of the neck of the mandible . TEMPORO MENDIBULAR JOINT TEMPOROMANDIBULA R JOINT Articulation Articulation occurs between the articular tubercle and the anterior portion of the mandibular fossa of the temporal bone above and the head (condyloid process) of the man- dible below. The articular surfaces are covered with fibrocartilage. TYPE OF JOINT The temporomandibular joint is synovial. The articular disc divides the joint into upper and lower cavities Capsule The capsule surrounds the joint and is attached above to the articular tubercle and the margins of the mandibular fossa and below to the neck of the mandible. LIGAMENTS The lateral temporomandibular ligament Its fibers run downward and backward from the tubercle on the root of the zygoma to the lateral surface of the neck of the mandible . This ligament limits the movement of the mandible in a posterior direction and thus protects the external auditory meatus. SPHENOMANDIBULAR LIGAMENT lies on the medial side of the joint It is a thin band that is attached above to the spine of the sphenoid bone and below to the lingula of the mandibular foramen . STYLOMANDIBULAR LIGAMENT It lies behind and medial to the joint and some distance from it. It is merely a band of thickened deep cervical fascia that extends from the apex of the styloid process to the angle of the mandible . The articular disc divides the joint into upper and lower cavities. It is an oval plate of fibrocarti- lage that is attached circumferentially to the capsule. It is also attached in front to the tendon of the lateral pterygoid muscle and by fibrous bands to the head of the mandi- ble. These bands ensure that the disc moves forward and backward with the head of the mandible during protrac- tion and retraction of the mandible . The upper surface of the disc is concavoconvex from before backward to fit the shape of the articular tubercle and the mandibular fossa; the lower surface is concave to fit the head of the mandible. Synovial Membrane This lines the capsule in the upper and lower cavities of the joint. Nerve Supply Auriculotemporal and masseteric branches of the mandibular nerve MOVEMENTS The mandible can be depressed or elevated, protruded or retracted. Rotation can also occur, as in chewing. In the position of rest, the teeth of the upper and lower jaws are slightly apart. On closure of the jaws, the teeth come into contact CLINICAL SIGNIFICANCE OF THE TEMPOROMANDIBULAR JOINT The temporomandibular joint lies immediately in front of the external auditory meatus. The great strength of the lateral temporomandibular ligament prevents the head of the mandible from passing backward and fracturing the tympanic plate when a severe blow falls on the chin. The articular disc of the temporomandibular joint may become partially detached from the capsule, and this results in its movement becoming noisy and producing an audible click during movements at the joint. DISLOCATION OF THE TEMPOROMANDIBULAR JOINT Dislocation sometimes occurs when the mandible is depressed. In this movement, the head of the mandible and the articular disc both move forward until they reach the sum- mit of the articular tubercle. In this position, the joint is unsta- ble, and a minor blow on the chin or a sudden contraction of the lateral pterygoid muscles, as in yawning, may be sufficient to pull the disc forward beyond the summit. In bilateral cases, the mouth is fixed in an open position, and both heads of the mandible lie in front of the articular tubercles Reduction of the dislocation is easily achieved by pressing the gloved thumbs downward on the lower molar teeth and pushing the jaw back- ward. The downward pressure overcomes the tension of the temporalis and masseter muscles, and the backward pressure overcomes the spasm of the lateral pterygoid muscles.
