Temporomandibular Joint PDF

The Temporomandibular Joint KATCHY AU. Classification This is a SYNOVIAL JOINT of CONDYLAR variety ARTICULATING SURFACES Temporomandibular joint (TMJ): is a synovial joint between the head (condyle) of the mandible and the mandibular fossa on the undersurface of the squamous p...

The Temporomandibular Joint KATCHY AU. Classification This is a SYNOVIAL JOINT of CONDYLAR variety ARTICULATING SURFACES Temporomandibular joint (TMJ): is a synovial joint between the head (condyle) of the mandible and the mandibular fossa on the undersurface of the squamous part of the temporal bone. The mandible is a single bone with a horizontal horseshoe-shaped body, which is continuous at its posterior ends with a pair of vertical rami, each ramus being surmounted by a head or condyle. ARTICULATING SURFACES The cranium, with which the mandible articulates, is also mechanically a single component, with a mandibular fossa on each side. This complex is in effect one functioning joint, as movement cannot take place at one temporomandibular joint without a concomitant movement occurring at the joint on the opposite side. The temporomandibular joints are thus the bilateral components of a craniomandibular articulation. Capsule: A dense, irregular collagenous connective tissue capsule encloses the articulating surfaces of the TMJ. It is attached above to the articular tubercle and the margins of the mandibular fossa and below to the neck of the mandible. Synovial Membrane The synovial membrane lines the capsule in both the upper and lower cavities of the joint. 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 and strengthens the lateral aspect of the capsule. This ligament limits the movement of the mandible in a posterior direction and thus protects the external auditory meatus. Ligaments: The sphenomandibular ligament 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 and lies on the medial side of the joint. It represents the remains of the first pharyngeal arch in this region. The stylomandibular ligament 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. Articular Disc: Meniscus: Is an oval plate of fibrocartilage articular disc that attaches circumferentially to the capsule that intervenes between the bony surfaces and divides the TMJ into upper and lower compartments. The upper surface of the disc is concavoconvex from anterior to posterior to fit the shape of the articular tubercle and the mandibular fossa; the lower surface is concave to fit the head of the mandible. The larger, superior compartment between the disc and temporal bone and permits some freedom of movement between the disc and articular eminence, while the inferior compartment encloses the entire neck of the mandible and is more firmly attached to the disc. Articular Disc: This attachment prohibits excessive movement between the disc and condyle. The disk attached in front to the tendon of the lateral pterygoid muscle and by fibrous bands to the head of the mandible. These bands ensure that the disc moves forward and backward with the head of the mandible during protraction and retraction of the mandible. Nerve Supply The joint capsule is richly endowed with sensory endings from the mandibular division of the trigeminal nerve by its branches of the auriculotemporal nerve. Additional innervation from the masseteric branch of the mandibular division of the trigeminal nerve. Blood Supply. Vascular supply to the joint is provided by branches of the superficial temporal and maxillary arteries as they approximate the joint. Muscles of mastication: These are a group of muscles that consist of the Temporalis, Masseter, Medial pterygoid Lateral pterygoid. The masticatory muscles attach to the mandible, and thus produce movements of the lower jaw at the temporomandibular joint (TMJ) to enable functions such as chewing and grinding. The principal muscles of mastication are developed from mesoderm of the first pharyngeal arch, and all of them are innervated by the mandibular division of the trigeminal nerve Temporalis muscle It is a fan-shaped muscle located in the temporal fossa. It is covered by tough temporal fascia which is attached above to the temporal line and below to the zygomatic arch. Origin: Floor of temporal fossa. Deep surface of the temporal fascia. Insertion: The fibres converge and descend to form a tendon, which passes through the gap between the zygomatic arch and the side of the skull. A. Temporalis muscle The muscle is inserted into: The medial surface, apex, anterior, border of the coronoid process of ramus of mandible. The anterior border of the ramus of mandible, almost up to the last molar tooth. Nerve supply: The temporalis is supplied by the anterior and posterior deep temporal nerves, the branches of the anterior division of the mandibular nerve. Action: The temporalis muscle elevates the mandible and so closes the mouth and approximates the teeth. Posterior fibres retract the mandible after it has been protruded. Temporalis muscle Superficial portion ZYGOMATIC PORTION Deep Portion B. Masseter The masseter is a thick quadrilateral muscle covering the lateral surface of the ramus of the mandible including its coronoid process. The condylar process is left uncovered. Origin: Superficial part: maxillary process of zygomatic bone, Inferior border of zygomatic arch (anterior 2/3) Deep part: deep/inferior surface of zygomatic arch (posterior 1/3) Insertion: Lateral surface of ramus and angle of mandible. B. Masseter Nerve supply: The masseter is supplied by a masseteric nerve, a branch from anterior division of the mandibular nerve. Action: It elevates the mandible causing a powerful jaw closure. The contraction of the superior part, which runs diagonally to the front, moves the mandible forward (protrusion). MASSETER MUSCLE LATERAL PTERYGOID MUSCLE This is a short, thick conical muscle with its apex pointing backwards. It passes backwards and slightly laterally from the roof and medial wall of the infratemporal fossa to the neck of the mandible. Origin: The lateral pterygoid consists of two heads, upper and lower: The upper smaller head arises from the infratemporal surface and crest of the greater wing of the sphenoid bone. The lower larger head arises from the lateral surface of the lateral pterygoid plate of the sphenoid bone  Insertion: The fibresLATERAL PTERYGOID MUSCLE of two heads run backwards and laterally, and converge to form a thick tendon, which is inserted into: Pterygoid fovea (is a small depression on the anteromedial surface of the condylar process) on the front of the neck of the mandible. Articular disc and capsule of the temporomandibular joint. Nerve supply: Lateral pterygoid is supplied by a branch of anterior division of the mandibular nerve LATERAL PTERYGOID MUSCLE Actions: Lateral pterygoids of two sides depress the mandible Lateral and medial pterygoid muscles of two sides acting together protrude the mandible. Lateral and medial pterygoid muscles of the two sides contract alternately to produce side-to-side movements. LATERAL PTERYGOID MUSCLE D)Medial Pterygoid The medial pterygoid is a thick quadrilateral muscle, situated in the infratemporal fossa. Origin: The small superficial head (a small slip of muscle) arises from maxillary tuberosity. The large deep head (forming the bulk of muscle) arises from medial surface of the lateral pterygoid plate. Insertion: The fibres run downwards, backwards, and laterally to be inserted by a strong tendinous lamina into a roughened area on the posteroinferior part of the medial surface and angle of ramus of mandible as high as the mandibular foramen and as forwards as the mylohyoid groove. D)Medial Pterygoid Nerve supply: The medial pterygoid is supplied by a nerve to medial pterygoid, a branch from the main trunk of the mandibular nerve. Actions: Medial pterygoids of two sides elevate the mandible to help in closing of mouth. Acting with lateral pterygoids, the medial pterygoids protrude the mandible D)Medial Pterygoid When medial and lateral pterygoids of one side act together, the corresponding side of the mandible is rotated forwards and to the opposite side Lateral and medial pterygoids of two sides when contract alternately produce side-to-side movements, which are used to grind the food. MEDIAL PTERYGOID MUSCLE SUMMARY MUSCLE ORIGIN INSERTION ACTION INNERVATION Temporalis Temporal fossa, deep Coronoid process of Elevates the Deep temporal surface of the the mandible and mandible; branch of the temporal fascia anterior border of unilaterally deviates mandibular nerve the ramus of the to the ipsilateral side; mandible; some retracts the mandible fibers insert into the from a protracted skeletal orbit of the position eye SUMMARY MUSCLE ORIGIN INSERTION ACTION INNERVATION Masseter Superficial : Superficial: Angle and Initiates elevation of Masseteric nerve Zygomatic process of lower, lateral surface the mandible and from the mandibular the maxilla and of the ramus of the adds force to closure; division of the anterior two thirds of mandible Middle: Mi contributes to trigeminal nerve the lower border of ddle of the ramus of clenching during the zygomatic the emotional stress and arch Middle: Anterior mandible Deep: Upp nocturnal clenching two thirds of the er ramus of the and bruxing; assists deep surface of the mandible and in protraction and zygomatic arch and coronoid process lateral deviation lower border of the zygomatic arch Deep: Deep surface of the zygomatic arch SUMMARY MUSCLE ORIGIN INSERTION ACTION INNERVATION Medial pterygoid Palatine bone and Medial surface of the Elevates the Medial pterygoid tuberosity of the ramus and mandible; protrudes branch of the maxilla mandibular angle the jaw; unilaterally mandibular division deviates the of the trigeminal mandible nerve contralaterally SUMMARY MUSCLE ORIGIN INSERTION ACTION INNERVATION Lateral pterygoid Superior Anterior head of the Opens and protrudes Lateral pterygoid head: Greater wing mandibular head, the mandible, pulls branch of the of the sphenoid articular capsule, and the disk forward, and mandibular nerve bone Inferior TMJ disk assists in the rotary head: Lateral surface motion of chewing; of the lateral acts with the medial pterygoid plate pterygoid to move the jaw side to side Superior head: Eccentrically controls the disk with a backward glide during closure Inferior head: Translates the mandibular head CLINICAL ANATOMY Masticatory muscle disorders include myofascial pain and dysfunction, myositis, and neoplasms. Myofascial pain and dysfunction may result from several etiologies. The most common ones are nocturnal bruxism, habitual clenching of the mouth, and whiplash injuries during a trauma. Temporomandibular joint (TMJ) dysfunction can result from an imbalance of forces within the muscles of mastication. Grinding of teeth at night (bruxism) is a common cause of TMJ dysfunction secondary to a resultant imbalance in the muscle of mastication forces from excessive grinding of the teeth. CLINICAL ANATOMY Muscle spasm of the muscles of mastication (trismus) can be a symptom of tumor or infection. An infection like tetanus may present with "lockjaw" or trismus. Other infections or inflammation of the muscles may present as myositis or pain during the movement of the jaw. Tumors, although rare but may present in the masticator space, which is enveloped by the deep cervical facia. These tumors may have an extension from adjacent regions. The medial side of the fascia is attached to the skull base, and the lateral side extends to the temporalis muscle. Anteriorly it is attached to the body of the mandible at the level of the oblique line, and posteriorly it is attached to the ramus of the mandible. CLINICAL ANATOMY Dislocation of the jaw, when uncomplicated, occurs only in a forward direction. When the mouth is widely open, the condyloid process of the mandible slides forward on to the articular eminence; from thence, a blow, or even a yawn, may cause forward dislocation into the infratemporal fossa on one or both sides. Upward dislocation can occur only in association with extensive comminution of the skull base, and backward dislocation with smashing of the bony external auditory canal and tympanic cavity which lie immediately behind the joint. CLINICAL ANATOMY Reduction is effected by pressing down on the molar teeth with the thumbs placed in the mouth, at the same time pulling up the chin; the former stretches the masseter and temporalis muscles which are in spasm, the latter levers the mandibular head back into place.