histo-structure&function of the temporomandibular joint

histo-structure&function of the temporomandibular joint...

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Unformatted text preview: 353 20' Structure and Function of the Temporomandibularjoint lames K.Averv and Sol Berniclt Introduction The nemporomandibular joint {Tell}, the mandibular articulation. is a bilateral diarthrosis between the condyles of the mandible and the articular eminenoes of the temporal bone. arteriorly. and the mandibular fos— sae. posteriody.‘l'he1hlj allows the mandible to move as a unit in both a hinge and a gliding movement. The TM] consists of: the condylar head of the mandible. the articulating surfaces of the temporal bone. the artic- ulating disc. and the articulating capsule. The disc sepa- rates the head of the condyles from the temporal bone. Therefore. the disc divides Illejoint into Ware portions, an upper and a lower compartment. The disc is an oval plate of fibrous tissues whose ]:Iseripher1llr blends into the artic- ulating capsule. [n fmnt. Use disc is anchored to the ten— '_ - _ ‘- _ __ _ _ _ dflnflfthelatflra] maid muscle. [ti-slight]! attachfid i-_ . ':Ill=_1.'_l_]ll.=ll:_'._|| -: I-:'_ -.|- lr'li' to the condyle. so that it follows thejaw in sliding move- '-" _ . ments. There are two synovial membranes in the joint: one lines the capsule above the disc. and the other lines the capsule below the disc. ' it loose arficular capsule is attached to the articular tubercles. the squamotpmpanic fissure. and the margins 0f the mandibular fDSSJ. benveen these tWO attachments. Below. it is attached to the neck of the mandible. so that pnsteriorlyr a portion of the mandible is intracapsular (Fig. 20.1}. The lateral {temporomandibular} ligament is inti- mateljlr related to the fibrous capsule. Above. it is attached to the zygoma. and below. it is attached to the lateral surfaces and posterior border of the neck of the mandible. - In addition. there are two accessel‘f ligaments associat- ed with the TMJ.'I11e stjrlomandibular ligament attaches to the styloid process and to the posterior border of the ramus; the sphenomandibular iigarne nt extends bebveen the spine olthe spennid bone and the lingula or the mandible (Fig. ZDJ C}. Fig. 20.1 A Dlagram of 1M} comparb'nents. B Diagram of lateral and posteri- orllgaments ofthe TM}. I: Dlagram of medial liga menls of the TM]. 354 ' lt'l Related Functional Tissues of the Oral and Pomoroi erreos Dbjectives Upper synovial cavity _ After reading this chapter you should be able to describe the structure of the condylcs. the temporal fossae. and the articulating disc and capsule. You should also be able to discuSs the function of this joint and the relation of the muscles of mastication to its actions. Histologlc Structure The microscopic structure of the TM] reveals a fibrous capsule enclosing the joint. which is' attached anteriorly to the articulating tubercle of the temporal bone above. and the neck of the condyle below {Fig 20.2}. Posteriorly. the capsule is attached to the temporal bone anterior to _ - - « - the external auditory canal above and the posterior Fig. 20.2 Diagram of the TM] 1rvith articular disc. capsule. and relations to the aspects of the condyle below {Fig 20.2} Suspended from lmalpte'l’flflid ““5033“ external auditory canal. the internal walls of the capsule bentreen the condyles ' . - and the fossae is the fibrous disc. which is composed of collagen fibers (fig. 20.3). “this disc is seen to separate the superior and inferior joint cavities. In this diagram. the cartilage is in the condylar head underlying the fibrous perichondrium. The condition indicates that the mandible has notlcompleted its growth. as cartilage has not been entirely replaced by bone. Growth occurs in the formation of new cells underlying the periochondrium of the condylar surface and also at the site of the trans— formation of cartilage to bone in the neck of the condyles. its long as there is cartilage in the conclylar head. growth mayr occur. Observe flie inclined plane of the anterior articulating surface of the condyle. the thin area of the articulating disc anteri trrljirr and the mic}: zone posteriorly (Fig 20.2}. Far posteriorly. a number of blood vessels appear. known as the vascular triangle (Fig. 20.3}. Above the vascular triangle. the elastic fibers of die disc emanate from the borders of the petrotympanic fissure. as seen in Figure 20.3. The articular disc is composed of collagen fibers. as sceri in Figure 20.4. Because the condylar head slides along the articular plane during - function. the capsule is described as loose. It is support— Fig. 20.3 Light micrograph of the posterior region ofthe glenoid fossa ed by a medial ligament tsphenomandibular}. a lateral shows location of elastic fibers attached to the petrotym pa pic fissure. “gag-"Enl- ltemporomandibular]. and a posterior figa- ment {stylornandibular]. These relative positions are seen' in Figures 20.13 and C. - Elastic. libero -- Petrotympanic fissure Flo. 20.4 Ultrasmrcuure of collagen fibers of the articular disr; a _- H». .— ..- moans-+4- ——- --..—-—--II-gan-—ra -_,_._._ -. 29 Structure and Function o the Tent oromono'ihulor oint 355 Conclyles Condyles are ovoid in shape mediolateraily and consist of a smooth bonyr surface covered with a fibrous connective tissue (Pig. 20.53}. The condyles grow laterally during development. gaining the oval shape as they reach matu- rity at E years of age. For example. the porous appearance of the cartilage—covered oondyle is apparent in Figure 205A. Histology of the condyle confirms in an ea rly— teenaged individual that the condyle has thinned consid- erably. with further thinning occurring as the age of the int] hrldual nears 2|] (Fig. 20.6). The condylar head and Fig. 2&5 Comparison ofa 6-year-old condyle [A] and adult tondyle {E}. head of long bones differ in that long bones form second— ND” the “was“! I" the lateral dimension. ary ossification sites {Fig 203]. These secondary ossifica- tion sites produce epiphyseal lines where lengthening of the long bone occurs. Like the heads of long bones. the oondylar heads grow by developing new chondroblasts. with growth of new cartilage matrix and replacement by bone. In long bones. however. the cartilage cells appear to be arranged in long rows adjacent to the cartilage hone . junctions. In the mandibular joint cartilage the cells appear scattered. as scen in figures 20.5 and Elli A Fig. ans A Histology of you rig postnatal codyle and disc. Reserve cartilage zone {EC}. multiplication of cells {MC}. cartilage zone. hypertrophy zone (HE). calcifying zone {CB}. B Thin cartilage zone later postnatally. bone for— mation {DEL Clinical Application "the most important formative time for the ml} is from the 3th to 12th weeks of embryonic age. Fit that time the condyIar heads differentiate and articulate with the temporal bone. which also' appears at this time. The articular disc then forms. and the capsule. ligaments. and masticatory mus- cles begin to differentiate. Any factor that would affect growth and differentiation at that time would be likely to alter development of the TM}. F lg. 24].? Diagrams ofthe cartilage of long bone in} and condyle [B]. Dbserve the lack of palisadlng and the thick perichondrium in the condyle. 356 H Related Functional Tissues of the Oral and Fomorol'Areos Temporomandlbular Fossa {Glenoid Fossa} The temporornandibular fossa is composed of an anteri- or zone in the form of an eminence [articular] and a pos— terior part. which is a depression or cavity on the inferiv or aspect of the Emporal bone. This fossa is located at the posterior medial end of the zygomatic arch (Fig. 2&8). To compensate for the increase in lateral dimen— sion of one condylar head. the glenoid fossa extends lat— erally as well! {Fig 20.8). By maturity. the articular emi— nence becomes prominent The articular eminences are smooth with rounded ridges on whose posterior slope the condyles slide during articulation. On the posterior wall of the fossa. the petrotympanjc fissure separates the anterior squamosa and the more posterior petrous parts of the temporal bone (Figs. 2111.3 and 24:13}. it is the only location in the disc in which elastic fibers are found. Hg. 213.3 Dmlopn‘bent ol‘ the glenoid {temporomaruiibular} fossa from birth Because Of theirIocation. these fibers may be a remnant to maturity. of the anterior llgament of the malleus. Synoyial Membrane a synoyial membrane [stratum synouiale] lines the entire articular capsule of the joint—both die upper and the lower compartments. The synouial cells appear to be a continuous layer. but usually are intermingled with connective—tissue fibers and fat cells. Thus, the synoiri— um is not a true membrane (Fig. Ella}. In this posterior region of the joint. synoyial folds may be found on the free surfaces of the joint ‘Wltl'lln these folds the cells may be piled up and may project into the cavity. Some folds may be norwascular while others have associated connective tissue or contain adipose cells (Fig. 20.10}. Ultrastructuraliy, it has been shown that there are two types of synoyial cells. types A and El {light and dark}. it has been suggested that type ii secretes hyaluronic acid. whereas type B produces a protein-rich secretion. The Fig. 20.9 Light micrognl ph of synoyial cells lining the Tit-i]. Fig. 2o.1o Ught micrograph of sinoyial and fat cells in the TM}. 20 Structure and Function o the Tent mandibular 'nt 35? matrix of the synovial memblane contains collagen fib- rils. unbanded fibrils. and election—dense amorphous material {Figlillli The synovial membrane is richly supplied wld'i blood vessels. Capillary networks are found not only in the subsynovial tissues. but also adjacent to the synovial cells. Three types of synovial capillaries are found: con— tinuous. fenestrated. and discontinuous. The fenestrated type is found in the matrix of the synovial membrane. Lymphatic vessels are observed a short distance from the synoviaI surface. draining into the capsular collecting lymphatic vessels. Synovial fluid. with hyaiuronic acid. is an infiltrate or distillate of the blood [as is tissue fluid}. Here. hyaluron- ic acid has a high viscosity and provides the lubricating property of synavial fluid. Vascular and Neural Supply Vascular Supply Blood is supplied to the TM] through branches of the superficial temporal, deep auricular: anterior Wait. and ascending pharyngeal arteries. These branches con— verge into the capsule of the joint [Pig 20.12}. Small arteries. arterioles. and capillaries pass into the periph- eral third of the atticulat disr. Note the extensive vascu- larity in the peripheral region of the disc. taken from a section of peripheral d'iird offl'iejoint [Fig 20.131.011 the other hand, a section of the central portion of the joint (Fig. 20.14] reveals that the thin portion of the disc is avascular. Note also the vascular diannels within the articular vessels: they have been injected with latex and the connective tissue has beat rernovetl. The high vascu- larity of the peripheral disc is dearly seen in Figure Fig. 20.13 1view olperipheral attitular disc. with blood vessels illustrated. Specimen is injected with ladia ink. Symvialoels Fig. 20.1 I Diagram oflight and dark synovial cells in the TM]. Circled inset is die diagmm ofa magnified yievvofflie upper syrtovial cavity. Fig. 20.14 1Ilrievv of central tone of articular disc inritl'usut blood vessels. Specimen is injected with lntl‘la ink. 358 H Related Functional Tissues of the [trial and Femoral Areas 20.15. Note mat the disc is oval and that its lateral and medial extremities are right and left respectively: its anterior aspect is above. and its more highlyI vascular‘ lzed posterior region is below. There are no vessels throughout the central portion of the disc. Neural Supply The nerve supply to the TM} is through the mandibular division of the trigeminal nerve. the same nerve that supplies the muscles of mastication. The neural branch- es are the uuriculobempornl. mosseteric. and deep tempo— ral nerves (Pig. ante]. Nerves containing rrnrelinared and nonmvelinated fihers enter the capsule and disc to sup- Aurlwlotemporal nerve Fig. 20.16 Dlagram of nerve su pplzl.r of the 'I'I'vI]. Aurlculotem poral masseteric plv the anterior. posterior. medial. and lateral regions of and deep temporal branches of the fifth nerve su pplv thejoinh AAnterior. the joint [1213. 20115} Nerve endings as receptars for pain. 3 Lilli-”rai- C POStenfi- - as well as such specialized nerve endings as receptors for Nerve ending - temperature. touch. and deep pressure. are found in. and pass from. the joint into the peripheral region of the articular disc and s_vnovial folds {Figs Zil'l'i“ and 20.18). lilnh.r free nerve endings. as receptors for pain. have been found in the peripheral region of the disc (fig. 2111?). The thin central portion of the disc is free of nerves. Both mvelinated and nonrnyelinated nerves are found in die connective-tissue core of the svnovial folds (Fig. 20.13}. Those nerves that terminate in various encapsulated structures appear to be coiled or globular in nature. and are embedded in the connective tissue of the articular disc or capSule {Fig 20.19}. in die condvlar region. mvellnated nerves are traced passing through Nerve endlng in synovlal fold Hg. 20.13 Neweending in the svnovial fold. Fig. 21119 Coiled nerve endlng In lil'beTMJ. . 26 Structure and Function o the Ten-I oromondihuler oint 359 the muscle to enter the capsular connective tissue. These nerves may end as nonmyelinated free nerve end— ings or specialized coiled endings. similar to Ruffini cor— puscles {Pig 2o.2tt]t . Muscles of Masticatlon There are eight powerful muscles of mastication. four on each side. Each has a different location: therefore. the direction of fiber contraction results in a different func- ~ tional relation Three of the muscles on each sldeuthe medial pterygoid. masseter. and temporalis—exert verti— . _ cai forces in closing the jawg whereas the function of the FEM“ mum ”Elma“ WPUEIE lateral pterygoid muscles is to protract the mandible and Fig. 202B Diagram oftypes of nerve endings In fliejuint capsule and disc stabilize the joint. These Inu5c1es do not function alone but worlt as a group with the musdes of the tongue and the superhyoid muscles. Free movements of the mandible relate to the interplay of masticatory musdes and the morphology of the teeth in the absence of food. Mesticutory movement. on the other hand. is the syner— Lateral gistic action of the three groups of muscles—the eleva- ”9'39““ ”“3?” tors. depressors, and protractors—that hinclion together and at different times during mastication of food. Medial The medial pren'goid muscle arises fmm the medial sur- face of the lateral pterygoid piate and inserts in the infe- rior surface of die ramus and angle of the mandible. Blood supplyr is from the maidllary artery, and nerve sup- ply from the mandibular division of the uigeminal. lt functions to prutract and elevate the mandible (Fig. 2:121].me this infefior view. the medial part is seen to run downward and backward below and behind the angle of; the mandible to meet the eitternailyr located masseter' in a tendinous raphe. and forming the pterygo— " masseteric sling (Figs. 2111.21 and 2m}, Fig 20. 21 Inien'or view oitl-Ie lateral and medial pterygoid muscles of masti- The let-em! ptet'jl'gflitf muscle has two heads: the upper “I'm - arising from me greater wing of the sphenoid and the lower from the lateral pterygoid plate. They insert into the front of the neck of the condyle and the capsule [Fig 21122}. Blood supply is from the maxillary artery. and nerve supply is from the pterygoid branch of the mandibular nerve. The function of both heads of me muscle is to protrude the mandible and pull the articu- lar disc forward (figs. 20.21 and 20.22}. The temporuiis muscles fibers originate from the floor of the temporal fossa and temporal fascia and insert on the anterior borders of the coronoid process and ramus of Clinical Application The TM] is a complex and precisely integrated bilat i eral joint with the functions of mastication and speech. By placing our fingers on the condylar heads and then opening and closing the Jaw. it is possible to follow the downward and foreword path of their sh dm g action Fig. 2f}. 22 Lateral view of the lateral and medial pterygoid muscles of masti- cation. 35fl W Related Functional Tissues o the Oral and Femoral Areas the mandible (Fig. EDIE). Blood supply is fmm the superficial temporal and maxillary arteries. and nerve supply is from the deep temporal branches of the mandibular nerve. Functions of the temporalis muscle are elevation of the jaw, retraction of the mandible, and clenching of the teeth. The mosseter muscle has a deep part and superficial part. The superficial fibers originate from the anterior two-thirds of the lower border of the zygomatic arch, and the deep fibers form the medial surface of the same arch. ”The superficial fibers are at right angles to the occlusal plane of the posterior teeth. and the deep fibers are directed dmymvard and slightly anteriorly. The masseter muscle inserts into the lateral surfaoe of the coroniod process of the mandible. the upper half of the tamu5. and the angle of the mandible. Blood supply is from the super— ficial temporal and maxillary arteries. and the nerve sup- ply comes from the mandibular division of the trigeminal nerve. The' functions of the masseter muscle are elevation oftl'te jaw and clenching of the teeth (Fig. 2024]. H9102} Temporalis muscle of mastication. _ _ . _ _ Functional and Elrnrcal Co nsrderatrons The sensations of pain and pressure are important symptoms in temporornandibular disorders. The nature of the transmission of these sensations-from tbisjoint is still not fully understood. In view of the previously described innervation of the joint pain and pressure may be explained by the following malfunctions: 1} Changes in occlusion,_frorn various causes, may produce displacement of the condyle—disc to disc—fossa relation and irritate the peripheral disc areas and associated nerve receptors: 2:! Inflammation and associated increases in synovial fluid would produce pressure effects and imitation of the specialized nerve endings in the synovial foids; 3] Muscle tensions may act on the nerves not only in muscle per se but also on the endings in the periosteal connective tissue. Disturbances to the TM] are, in part. no different from those in otherjoints. There are dissimilarities in the dis— orders of the TM]. however. as a result of its 'speciflc anatomic and functional features. The Tl'vljs are bilateral- ly ooupled as a single unit by the mandible, which pre- vents unilateral motion. Its aru' cular surfaces are covered ' by articular fibrous tissue mther titan hyaline cartilage. and are found in other joints. There is a functional rela— tion with the dentition. periodontal tissues, muscles of mastication. and the joint. Pathology in one oomponent may affect another. which complicates diagnosis of a disease; therefore, the Til-Ii] is exposed to functional changes seen in the oral cavity. ' ' Flg. 20.24 Ivlasseterrnuscle ofmastlcatlon. Clinical Application . Developmental Disturbances Myofacial pain dysfunction is usually a result of masticatory muscles spasms, and themajor cause is psychologic stress. There are four cardinal symptoms: preauricular pain. muscle tenderness, limitation of mouth opening. and clicking. Although uncommon. developmental disturbances do occur. Condylar aplasia may occur either unilaterally or bilaterally. Usually, it is associated with other anatomi- 205tructure and Functiono the Tent oromondibuior oint 361 cally related defects. such as a defective or absent eater- Clinical Application nal ear. The intimate relation In the development of the external ear. mandible. and TM] may darify this associa— tion. Underdevelopment or defective formation of the mandibular condyle may be congenital or acqtfired as a result of toxic agents interfering with normal prenatal and postanatal development of the condyle. These defects may result from...
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