TEMPOROMANDIBULAR JOINT (TMJ)

 Overview and Topographic Anatomy 

• The temporomandibular joint (TMJ) is the articulation between the squamous portion of the temporal bone and the the condyle of the mandible 
• It is a ginglymoarthrodial joint because it has both a hinge and a gliding action 

STRUCTURAL COMPONENTS 

• The TMJ comprises 2 types of synovial joints-hinge and sliding-and consists of the following:

1. Squamous portion of the temporal bone
2. Articular disc (contained within the TMJ)
3. Condyle of the mandible
4. Ligaments (also serve as boundaries)

TMJ SYSFUNCTION 

• Affects 33% of the population and may be severe 
• Causes include arthritis, trauma, infection, bruxism, and disc displacement 
• More common in females

OSSEOUS STRUCTURES

Squamous Portion of the Temporal Bone

The TMJ articulation is located on the squamous portion of the temporal bone  Has an avascular articular surface composed primarily of fibrous connective tissue and some fibrocartilage instead of  hyaline cartilage   The main load-bearing areas are on the lateral aspect of the squamous portion, condyle, and articular disc  The dense fibrous connective tissue is thickest in the load-bearing areas  :Relations of the squamous portion of the temporal bone  Anterior-articular eminence  Intermediate-glenoid fossa  Posterior-tympanic plate tapering to the postglenoid tubercle

structure  comments  Articular eminence  The strong bony prominence on the base of the zygomatic process  Articular tubercle   The lateral part of the articular eminence is referred to as articular tubercle and provides attachment for the capsule and lateral temporomandibular ligament   Glenoid fossa  The depression into which the condyle is located Superior to this thin plate of bone is the middle cranial fossa  The anterior boundary of the glenoid fossa is the articular eminence  The posterior boundary of the glenoid fossa is the tympanic plate   The glenoid fossa can be divided into 2 parts by the squamotympanic fissure (lateral) and the petrotympanic fissure (medial):  Anterior articular area-squamosal part of the temporal bone (this is where the articulation occurs)  Posterior nonarticular area-tympanic portion ( parotid gland may extend into this area)  Tympanic plate  The vertical plate located anterior to the external auditory meatus  Postglenoid tubercle  An inferior extension of the squamous portion of the temporal bone   Makes the posterior sapect of the glenoid fossa  Provides attachment for the capsule retrodiscal pad

Mandibular Condyles

Articulate with the articular disc  Ovoid in shape:  Mediolateral- 20mm  Anteroposterior- 10mm   Articular surface is avascular fibrous connective tissue instead of hyaline cartilage   The main load-bearing areas are on the lateral aspect

ARTICULAR DISC

Composed of dense fibrous connective tissue  Located between the squamous portion of the temporal bone and the condyle  Is avascular and aneural in its central part but is vascular and innervated in the peripheral areas, where load-bearing is minimal   The main load-bearing areas are located on the lateral aspect; this is an area of potential perforation   Merges around its periphery, attaching to the capsule  Divided into 3 bands:  Anterior-this thick band lies just anterior to the condyle with the mouth closed  Intermediate-this band, the thinnest part, is located along the articular eminence with the mouth closed  Posterior-this thick band is located superior to the disc with the mouth closed   Additional attachments:  Medial/lateral-strong medial and lateral collateral ligaments anchor the disc to the condyle  Anterior-the disc is attached to the capsule and the superior head of the lateral pterygoid, but not the condyle, allowing the disc to rotate over the condyle in an anteroposterior direction  Posterior-the disc is contiguous with the bilaminar zone that blends with the capsule

BILAMINAR ZONE (Posterior Attachment Complex)

A bilaminar structure located posterior to the articular disc  Highly distortable, especially on opening the mouth  Composed of:  Superior lamina (stratum)-contains elastic fibers and anchors the superior aspect of the posterior portion of the disc to the capsule and bone at the postglenoid tubercle and tympanic plate   Retrodiscal pad-the highly vascular and neural portion of the TMJ, made of collagen, elastic fibers, fat, nerves, and blood vessels (a large venous plexus fills with blood when the condyle moves anteriorly)  Inferior lamina (stratum)-contains mainly collagen fibers and anchors the inferioraspect of the posterior portion of the disc to the condyle

TMJ COMPARTMENTS

The articular disc divides the TMJ into superior and inferior compartments   The internal surface of both compartments contains specialized endothelial cells that form a synovial lining that produces synovial fluid, making the TMJ a synovial joint  Synovial fluid acts as:  A lubricant  A medium for providing the metabolic requirements to the articular surfaces of the TMJ

Superior compartment   Between the squamous poetion of the temporal bone and the articular disc   Volume = 1.2 ml  Provides for the translational movement of the TMJ  Inferior compartment  Between the articular disc and the condyle   Volume = 0.9 ml   Provides for the rotational movement of the TMJ

CAPSULE AND LIGAMENTS

Capsule

Completely encloses the articular surface of the temporal bone and the condyle   Composed of fibrous connective tissue  Toughened along the medial and lateral aspects by ligaments   Lined by a highly vascular synovial membrane  Has various sensory receptors including nociceptors  Attachments:  Superior-along the rim of the temporal articular surfaces  Inferior-along the condylar neck  Medial-blends along the medial collateral ligament  Lateral-blends along the lateral collateral ligament  Anterior-blends with the superior head of the lateral pterygoid m.  Posterior-along the retrodiscal pad

Ligaments

Collateral ligaments  Composed of 2 ligaments:  Medial collateral ligament-connects the medial aspect of the articular disc to the medial pole of the condyle  Lateral collateral ligament-connects the lateral aspect of the articular disc to the lateral pole of the condyle   Frequently called the discal ligaments  Composed of collagenous connective tissue; thus, they are not designed to stretch  Temporomandibular (lateral) ligaments  The thickened ligament on the lateral aspect of the capsule  Prevents posterior displacement of the condyle  Composed of 2 separate bands:  Outer oblique part-largest portion; attached to the articular tubercle; travels posteroinferiorly to attach immediately inferior to the condyle; this limits the opening of the mandible  Inner horizontal part-smaller band attached to the articular tubercle running horizontally to attach to the lateral part of the condyle and disc; this limits posterior movement of the articular disc and the condyle  Stylomandibular ligaments  Composed of a thickening of deep cervical fascia   Extends from the styloid process to the posterior margin of the angle and the ramus of the mandible  Helps limit anterior protrusion of the mandible  Sphenomandibular ligament  Remnant of Meckels cartilage   Extends from the spine of the sphenoid to the lingula of the mandible Some authors suggest it may help act as a pivot on the mandible by maintaining the some amount of tension during both opening and closing of the mouth   Some authors suggest it may help limit anterior protrusion of the mandible   Is the ligament most frequently damaged in an inferior alveolar nerve block

• Up to 33%of adults have a TMJ-related problem
• Perforations of the articular disc typically occur in the later stages of TMJ dysfunction
• Women have a higher prevalence of disc perforations than men 
• Many factors may contribute to changes in the disc:

1. Bruxism
2. Trauma
3. Lateral pterygoid muscle abnormal activity 
4. Overloading

• Most disc perforations occur in the lateral or posterior portions of the disc and vary in size
• Crepitus and clicking sounds on opening the mouth are common clinical manifestations
• Anterior disc displacement also is common
• Mandibular dislocation ( or subluxation of the TMJ ) occurs when the condyle moves anterior to the articular eminence

1. With dislocation, the mouth  appears "wide open"
2. Because the condyle is displaced anterior to the articular eminence, a depression can be palpated posterior to the condyle 

• Spontaneous dislocations can occur from a variety of actions ranging from a simple yawn to an extended dental treatment
• Because the mandible is dislocated, the patien has a great deal of difficulty verbalizing his or her predicament
• Relocation involves repositioning the condyle posterior to the articular eminence
• Opening the mandible involves a complex series of movements 
• Initial movement is rotational, which occurs in the lower TMJ compartment:

1. Lateral pterygoid ( inferior head) initiates the opening of the jaw (the superior head of the lateral pterygoid is described as being active during elevation of the mandible in a "power stroke")
2. As the mandible is depressed, the medial and collateral ligaments tightly attach the condyle to the articular disc, thereby allowing for only rotational movement
3. Once the TMJ becomes taut, no further rotation of the condyle can occur 
4. Normally, rotational movement continues until the upper and the lower teeth are about 20 mm away from each other

• For additional/further opening of the mandible, translational movement must occur:

1. A translational movement occurs in the upper TMJ compartment and provides for most of the mandible's ability to open
2. In this movement, the articular disc and the condyle complex slide inferiorly on the articular eminences, allowing for maximum depression of the mandible

ARTHRITIS

• Arthritis is the most common cause of pathologic changes in the TMJ
• When rheumatoid arthritis occurs, usually both TMJs are affected, and other joints tend to be affected before the TMJ
• Radiologic images in the initial disease stages show decreased joint space without osseous changes
• Radiologic images in the late disease stage show decreased joint space with osseous changes, possibly including ankylosis 
• In osteoarthritis, causes include normal wear, trauma, and bruxism, and clinical manifestations may range from mild to severe

ANKLYOSIS

• Anklyosis is an obliteration of the TMJ space with abnormal osseous morphologic features, which often occurs as a result of trauma or infection
• Classified as either true (intracapsular) or false (extracapsular, usually associated with an abnormally large coronoid process or zygomatic arch) ankylosis 
• Treatment varies in accordance with the cause but may include a prosthetic replacement or condylectomy
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