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GROSS ANATOMY This is a synovial joint of condylar variety. Articular surfaces- A. upper part - a) Articular eminence, b) ant. part of mandibular fossa. B. inferior surface - a) head of the mandible.

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The temporomandibular joint is the joint of the jaw and is frequently referred to as TMJ. The TMJs are one of the only synovial joints in the human body with an articular disc. The name is derived from the two bones which form the joint : the upper temporal bone which is part of the cranium and the lower jaw bone called the mandible.


COMPONENTS There are six main components of the TMJ. Mandibular condyles Articular surface of the temporal bone Capsule Articular disc Ligaments Lateral pterygoid


CAPSULE and ARTICULAR DISC The capsule is a fibrous membrane that surrounds the joint and incorporates the articular eminence. It attaches to the articular eminence, the articular disc and the neck of the mandibular condyle. The articular disc is a fibrous extension of the capsule in between the two bones of the joint. The disc functions as articular surfaces against both the temporal bone and the condyles and divides the joint into two sections, as described in more detail below. It is biconcave in structure and attaches to the condyle medially and laterally.

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The anterior portion of the disc splits in the vertical dimension, coincident with the insertion of the superior head of the lateral pterygoid. The posterior portion also splits in the vertical dimension, and the area between the split continues posteriorly and is referred to as the retrodiscal tissue.


LIGAMENTS The ligaments are-the fibrous capsule,the lateral ligament,the sphenomandibular ligament,stylomandibular ligament. The fibrous capsule- attached above to articular tubercle,below to mandible,circumference of mandibular fossa The lateral ligament- attached above to articular tubercle,below to posterolateral aspect of neck of mandible. The sphenomandibular ligament- attached superiorly to spine of sphenoid,inferiorly to lingula.it is accessory ligament. The Stylomandibular ligament- attached above to lateral styloid process and below to angle of mandible.it is also accessory.


ARTICULATION The TMJ is a ginglymoarthrodial joint, referring to its dual compartment structure and function (ginglymo-and arthrodial). The condyle articulates with the temporal bone in the mandibular fossa. The mandibular fossa is a concave depression in the squamous portion of the temporal bone.

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There are two TMJs, one on either side, working in unison. The unique feature of the TMJs is the articular disc. The disc is composed of fibrocartilagenous tissue which is positioned between the two bones that form the joint. The disc divides each joint into two. The lower joint compartment formed by the mandible and the articular disc is involved in rotational movement-this is the initial movement of the jaw when the mouth opens. The upper joint compartment formed by the articular disc and the temporal bone is involved in translational movements-this is the secondary gliding motion of the jaw as it is opened widely.


MUSCLE PRODUCING MOVEMENTS Depression- lateral pterygoid mainly Elevation- masster,temporalis,medial petygoid of both sides. Protrusion- lateral and medial pterygoid. Retraction- posterior fibres of temporalis. Lateral or side to side movement eg.turning chin to left side- left lateral pterygoid and right medial pterygoid.




DEVELOPMENT Approximately at 10 weeks the components of the future joint become evident in mesenchyme btw the condylar cartilage of mandibular bone and temporal bone. Two slit like joint cavities and an intervening disk make their appearance by 12 weeks. The mesenchyme around it forms fibrous capsule. The developing sup. Head of lat. Pterygoid muscle attaches the ant. Portion of the fetal disk. The disk also continues post. Through the petrotympanic fissure and attaches to the malleus of the middle ear. This connection is obliterated by growth of lips during development.


HISTOLOGY Bony structures Articular fibrous covering Articular disk Synovial membrane


BONY STRUCTURES The condyle of the mandible is composed of cancellous bone covered by thin layer of compact bone. The trabeculae are grouped in such a way that they radiate from the neck of the mandible and reach the cortex at right angles,thus giving max. strength to the condyle. Due to growth hyaline cartilage lies underneath the fibrous covering,it grows by apposition from the deepest layers of connective tissue.

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At the same time deep surface is replaced by bone. This is called secondary cartilage because it is not organized in parallel rows of cells at the interface btw forming bone and the cartilage. The roof of glenoid fossa consists of compact bone,articular eminence consists of spongy bone.


ARTICULAR FIBROUS COVERING TMJ, unlike other synovial joints,the articular surfaces are covered with fibrous tissue, because mandible is formed from membranous ossification and there are no cartilages present. Its superficial layer consists of network of strong collagenous fibres. The deepest layers are rich in undifferentiated cells as long as hyaline cartilage is present in condyle.this zone is names as reserve cell zone. Its presence increases the capacity to withstand mechanical stress.

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In articular areas it shows a definite arrangement of two layers with transition in between, the inner zone fibres are at right angles to bone while outer zone fibres are parallel to it. No continuous cellular lining is on its free surface. only isolated fibroblasts are present here.

Is TMJ a weight bearing joint?? : 

Is TMJ a weight bearing joint?? The presence of wavy collagen fibres both in articular disk and in fibrous tissue are suggested to be due to compression and are sighted in support of weight bearing nature. The finding of chondritin sulphate as principal GAG present in disk is subjected to compression loads,as in weight bearing joints. However absence of cartilage covering the articular surface is cited as a point against weight bearing nature of TMJ.


ARTICULAR DISK In young individuals it is composed of dense fibrous tissue elastic fibres are few. the fibroblasts in the disk are elongated and send flat cytoplasmic process into interstices btw the adjacent bundles. With advancing age due to mech. stress some cells starts appearing rounded in shape similar to chondroid cells, they are not true since they lack capsule around themselves.the presence of chondrocytes may increase resistance and resilience of fibrous tissue. The fibrous tissue at articular eminnence,condyle,central area is devoid of vascularization and innervations therefore has limited reparative ability.


SYNOVIAL MEMBRANE The articular capsule is lined with a synovial membrane that folds to form synovial villi.villi projects into joint spaces.It stretches during movement and remain folded during rest. It consists of internal cells which do not form continuous layer but shows gaps and the subintimal connective tissue layer ,rich in blood capillaries.

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These intimal cells are of three types-a)fibroblast like or B-cell-rich in RER.they are sometimes called S-cell cause of their secretory function.b)macrophage like or A-cell-no RER contains more golgi complexand lysosomes.c)has celular morphology btw A and B types. Synovial fluid acts as nutrition for avascular tissues.as age increaes the amount of synovial fluid decreases and villi increases. Synovial membrane has considerable potential to regenerate.


CLINICAL CONSIDERATIONS The most common disorder of the TMJ is disc displacement. The most common cause of TMJ pain is myofascial pain dysfunction syndrome, primarily involving the muscles of mastication. Internal derangements is defined as an abnormal relationship of the disc to any of the other components of the TMJ. Disc displacement is an example of internal derangement. Degenerative joint disease, otherwise known as osteoarthritis is the organic degeneration of the articular surfaces within the TMJ. TMJ pain remains one of the most reliable diagnostic criteria for temporal arthritis.

Diagnosis and Treatment of TMJ : 

Diagnosis and Treatment of TMJ TMJ is usually determined by exams, such as x-ray, MRI and CT scan. If the condition is not serious, a physician will usually recommend several steps: • Resting the jaw joint• Utilizing conventional analgesic pain killers or nonsteroidal anti-inflammatory drugs to alleviate the swelling and tight muscles• Applying heated compresses to the areas• Avoiding strain of the jaw • Avoiding tough foods that require heavy chewing



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