Intra-articular tissue in the temporomandibular joint

Intra-articular Ahmed

tissue

S. El Mahdy,

in the temporomandibular

joint

B.Ch.D., F.D.S.*

Faculty of Dentistry, Cairo University, Cairo, U. A. R.

A

rticles presenting

discussions of the structures of the tissue which separate the joint into an upper and a lower compartment are numerous. However, lack of agreement on its description and nomenclature causes confusion. This article reviews relevant literature and correlates it with personal observations of the functional anatomy of this tissue. A complete descriptive terminology is proposed.

temporomandibular

REVIEW

OF THE LITERATURE

The tissue which divides the temporomandibular joint into an upper and lower compartment is referred to as intra-articular tissue in this article. The nomenclature of this tissue varies according to individual interpretation and method of examination. According to some authors, the term articular disc includes all the intraarticular tissue, while for others, the articular disc is merely a part of the intraarticular tissue. Bellingerl described the articular disc as an oval biconcave structure of dense fibrous connective tissue with a few interposed cartilaginous cells. Markowitz and Gerry2 noted that the posterior attachment of the disc to the joint capsule was loose tissue which hemorrhaged freely when the disc was removed surgically. Dixon3 utilized a photomicrograph of a median sagittal section of the intraarticular tissue when he described the disc as having an anterior part composed of densely woven fibrous tissue and a posterior part which was loose and open in texture (Fig. 1A). The dense collagenous anterior part of the intra-articular tissue is corlsi&red by some authors to be the entire extent of the articular disc.1~6 Terms like tP/orkiag area of the disc and disc proper also appear in the literature.7 The loose posterior structure is given various names such as the posterior disc,al attachment or retrodiscal pad.4 ZenkeP considered the posterior part of the intra-articular tissue to be part of the posterior wall of the joint capsule and described the entire stru+cture as ;(

plastic retroarticular

cushion.

*Associate Professor, Prosthetic 396

Department.

Volume 26 Number 4

Intra-articular

tissue in TMJ

Fig. 1A. Classification and terminology of the structure of the temporomandibular cording to Dixons: A, the central dense part; B, the posterior loose part.

joint

397

ac-

Oberg and associates9 described the disc as being composed of three parts. These were (1) a thin central part with dense collagenous tissue, (2) surrounded by a thick intermediate part and, beyond that, (3) a peripheral part with loose tissue (Fig. 1B). ReeslO considered all of the intra-articular tissue to be the disc. He described it as being composed of the anterior band, the intermediate zone, the posterior band, and the bilaminar region (Fig. 1C). He considered the bilaminar region to be composed of a superior stretchable stratum attached to the anterior lip of the squamotympanic fissure and an inferior stratum attached to the inferior margin of the posterior articular slope of the condyle. emphasized that the intra-articular tissue is Krogh-Poulsen and MBlhave’l thicker medially than Iaterally and that it has a lateral and a medial triangular extension attached to the poles of the condyles.

METHODS OF INVESTIGATION Mandibular joints of four fresh cadavers were removed en bloc. The joints were divided in a sagittal section with a saw, and the intra-articular tissue was examined in situ and was photographed (Figs. 2 and 3). From other mandibular joints, intra-articular tissue was dissected and photographed in a sagittal plane to demonstrate its form in cross section (Fig. 4). Intra-articular tissue was removed from three cadavers and photographed with light transmitted through the tissue. This method demonstrated the thickness of the different parts of the intra-articular tissue as suggested by the opacity (Fig. 5).

1 Prosthet.

398 El Mahdy

October,

Dent. IS71

Fig. 1B. Classification and terminology of the structure of the temporomandibuiar joint a<.cording to Oberg and associatesg: A, the central dense part; 23, the thick intermediate portions ; C, the peripheral zones.

POSTERIOR

ANTERIOR

BILAMIHAR PO ‘Si.BANDINTERMED. ZONE ,’ POST.TEMFWl : REGION :

Fig. 1C. Classification and terminology of the structure of the temporomandibula .r joint ac. cording to Rees.10 Intra-articular tissue front two joints was prepared histologically to provide serial sagittal and coronal sections. The sections were stained with hematosylin and eosin and with van Gieson-Hansen stains and were examined under the microscope. Certain sections were photographed to demonstrate the shape of the intra-articular tissue in cross section (Fig. 6) ,

Intra-articular

Fig. 2. A sagittal

section

of a mandibular

joint.

The condyle

tissue in TMJ

is located

below

399

the articular

fossa.

Fig. 3. The intra-articular tissue divides the mandibular joint into two compartments (A and B). The structure, direction of fibers, and relative size of the bilaminar zone are clearly depicted in these two pictures.

I. Prosthet. Dent October. 1971

Fig. 4. Sagi Itl.a1 cross section of the intra-articular

Fig. 5. Intra-articular tissue photographed thickness of its different parts: A, anterior;

tissw.

under transmission of light indicates P, posterior; M, medial; L, lateral.

the relative

Intra-articular

Fig. 6. Photomicrographs

of (A)

sagittal

tissue in TM]

and (B) corona1 sections of the intra-articular

401

tissue.

402

El Mahdy

.I P~osthet. Dent. Ocrobrr, 1971

OBSERVATIONS The intra-articular tissue always divided the temporomandibular joint into two compartments (Figs. 2 and 3). When the condyle was moved along the articular eminence, the shape of thr flexible intra-articular tissue was influenced by its relationship to the bony components of the joint. When this tissue was examined out of contact with bone while the condyle was below the articular fossa, its neutral shape was in general conformit! with the bony contours of the mandibular joint (Fig. 2). The inferior surface oi the intra-articular tissue was concave and conformed to the condyltt, while its superior surface was convex posteriorly and saddle-shaped anteriorly (Figs. 2 and 4). In this position, the superior surface extended more anteriorly and less posterior& than did the inferior surface (Fig. 2). The intra-articular tissue was attached to the medial and lateral poles of’ thr condyle by two thin fibrous triangular extensions. The remainder of the intraarticular tissue was not uniform in thickness (Fig. 4). An anteroposterior section (Figs. 4 and 6, A) could be divided into four parts similar to those suggested b) Rees.lO The medial part of the intra-articular tissue was generally thicker than tht: lateral part. This variation in thickness \vas more obvious in the posterior thick dense part of the tissue (Figs. 5 and 6, B) . The bilaminar zone contained loose stretchable tissue in contrast to the remainder of the intra-articular tissue (Fig. 3) . I n a sagittal section, the bilaminar zone appeared triangular in shape (Fig. 3> A) and capable of attaining considerable as reported by size when stretched (Fig. 3, B). Th is zone seemed to be laminated Rees.l” The superior stratum passed from the dense fibrous part of the intraarticular tissue to the temporal bone, while the inferior stratum passed from the dense part of the intra-articular tissue to the posterior surface of the neck of thp condyle. However, the outer posterior fibers (stratum) of the capsule ran almost vertical from the temporal bone to the condylar neck (Fig. 3, B) . DISCUSSION The descriptive terminology generally applied to the intra-articular tissue is based mainly on the distribution and morphology of the connective tissue. However, other factors, such as the nerve and blood supply and functional significance, also should be considered. A term like working area 01 the disc attempts to emphasize function, while disc proper7 suggests that the intra-articular tissue consists of some structures that are functionally adapted to act as discs while others are not. The location and orientation of these structures should be precisely described. The description of the intra-articular tissue by Dixon,3 which is based on a sagittal cross-section view (Fig. IA), and by Clberg and associates,@ who use the terms central, intermediate, and peripheral zone (Fig. IB), may cause confusion when compared with Rees’ description (Fig. 1C) . Thus, the intermediate zone (Fig. 1~) 9 may refer to either the anterior or the posterior band in Rees’ description’0 and the peripheral zone@ may be interpreted to be either the bilaminar zone or the anteriol attachment of the intra-articular tissue to the external pterygoid muscle.

Intra-articular

tissue in TMJ

403

Rees’ nomenclature based on the morphology and distribution of the fibrous tissue seems to offer the most logical terminology suggested so far. However, a slight modification may provide a more complete description of the intra-articular tissue in relation to its function. For example, the two attachments of the intra-articular tissue to the condyle below its medial and lateral poles should be described as separate entities. They are triangular extensions of the intra-articular tissue with blood and nerve supplies. The lateral attachment contains more nerve endings12, I3 and less blood supply4 than the medial attachment. The variation in thickness of the tissue, especially the posterior band as seen from a coronal aspect (Fig, 6, B) , should also be considered, because the wedge shape of this tissue might contribute to its adaptive properties during function. The term articular disc in relation to the intra-articular tissue has been rather loosely defined. For example, in Rees’lO terminology, the term articular disc represents all of the intra-articular tissue, while Sicher” does not consider the bilaminar zone to be a part of the disc. He considers the disc to be the pressure-bearing part which is free of nerves and not covered by a synovial layer. However, the role of the anterior and posterior band of the intra-articular tissue is not mentioned in Sicher’s description. If the use of the term articular disc should be continued, its extent should be defined in accordance with the description of the intra-articular tissue. PROPOSED

NOMENCLATURE

AND

RATIONALE

The following nomenclature is offered to overcome the confusion and to define more clearly the component parts of the intra-articular tissue (Fig. 7). The term intra-articular tissue includes all tissue that separates the temporomandibular joint into two compartments. The intra-articular tissue consists of ( 1) an anterior band, (2) an intermediate zone, (3) a posterior band, (4) a bilaminar zone, (5) a medial attachment, and (6) a lateral attachment. The anterior band can be considered to be an anterior limiting barrier. The anterior band may help limit the forward translation of the condyle in extreme opening. The intermediate zone is the dense flexible avascular sagitally biconcave part of the intra-articular tissue. The intermediate zone is positioned between the condyle and articular eminence in condylar protrusion and is anatomically adapted to support the condyle when it slides under pressure over the articular eminence. The posterior band is thick and wedge shaped and has blood and nerve supplies. The posterior band may act to protect the thin roof of the articular fossa from heavy pressure. Being wedge shaped, the posterior band is capable of adaptive mobility. The bilaminar zone is anatomically adapted to allow functional movement of the dense parts of the intra-articular tissue and contains vascular elements required for the nutrition of the dense part. The vascular medial attachment contains nerve endings but to a lesser degree than does the lateral attachment. These nerve fibers may transmit information about the functional state of the mandibular joint.

404

1 l’,osthet. Octobrl-.

El Mahdy

Dent 1971

la fermi wail pP capsule

Fig. 7. Suggested terminology

of the intra-articular

tissue modified

after Rees.lQ1

The anterior band, the intermediate zone, and the posterior band which together form the dense part of the intra-articular tissue may be termed the articular disc, since it functions as discs do in other joints. SUMMARY The intra-articular tissue of the human temporomandibular joint was described, and a terminology in accordance with both function and structure of the tissue was suggested. The term articular disc should be related to this description of the intraarticular tissue. The author wishes to thank Professor W. Krogh-Poulsen, Chairman of the Department of Stomatognathic Physiology and Dysfunction, Royal Dental College, Copenhagen, for his assistance, suggestions, and encouragement in preparing this article and to Professor Z. Kasloff’

of the Faculty of Dentistry, writing

University

of Manitoba,

for his suggestions and assistance in

this manuscript.

References 1. Bellinger, D. H.: Present Status of Arthrosis of the TemporomandibuIar Joint, J. Oral Surg. 6: 9-16, 1948. 2. Markowitz, H. A., and Gerry, R. G.: Temporomandibular Joint Disease, Oral Surg. 2: 1309-1337, 1949.

Fv’duge; 2j

Intra-articular

tissue in TM]

405

and Functional Significance of the Intra-articular Disc of the 3. Dixon, A. D.: Structure Human Temporomandibular Joint, Oral Surg. 15: 48-61, 1962. 4. Boyer, C. C., Williams, T. W., and Strevens, F. H.: Blood Supply of the Temporomandibular Joint, J. Dent. Res. 43: 224-228, 1964. ed. 4, St. Louis, 1957, The C. V. Mosby 5. Orban, B. J.: Oral Histology and Embryology, Company. 6. Sicher, H.: Structure and Functional Basis for Disorders of the Temporomandibular Articulation, J. Oral Surg. 13: 275-279, 1955. I. A.: The Movement of the Mandibular Intra-articular Disc, Proc. R. Sot. 7. Findlay, Med. 58: 671-675, 1965. plastische Polster des Kiefergelenkes und seine mechan8. Zenker, W.: Das retroarticulare ische Bedeutung, Z. Anat. Entwicklungsgesch. 119: 375-388, 1956. 9. Oberg, T., Carlsson, G. E., Fajers, C. M., and Bergman, F.: Aging of the Temporomandibular Disc With Special Reference to the Occurrence of Cartilaginous Cells, Odontol. Foren. Tidskr. 74: 122-129, 1966. Joint, Br. Dent, J. 96: 12510. Rees, L. A.: The Structure and Function of the Mandibular 133, 1954. A.: Om discus articulationis temporomandibularis, W., and Mslhave, 11. Krogh-Poulsen, Tandlaegebladet 61: 265-271, 1957. B. C., Jr.: Nerve Endings in the Temporomandibular Joint 12. Keller, J. H., and Moffett, of the Rhesus Macaque, Anat. Rec. 160: 587-593, 1968. of the Temporo-mandibular Joint Capsule in Man, Trans. B.: Innervation 13. Thilander, Roy. Schools Dent. (Stockholm and Umea), Ser. 2, No. 7, 1961. 61 STREET 9 MAADI, CAIRO U. A. R.