Book - Oral Histology and Embryology (1944) 13

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Orban B. Oral Histology and Embryology (1944) The C.V. Mosby Company, St. Louis.

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Chapter XIII Temporomandibular Joint

1. Anatomic Remarks

The mandibular articulation (temporomandibular joint) is a diarthrosis between mandibular fossa and articular tubercle of the temporal bone, and capitulum (head, condyle) of the mandible. A fibrous plate, the articular disc, intervenes between the articulating bones.

The articulating surface of the temporal bone is concave in its posterior, convex in its anterior part. The 91131 concavity, articular fossa, extends from the squamotympanic and petrotympanic fissure in the back to the con vex articular tubercle in front. Th latter is strongly convex in a sagittal and slightly concave in a frontal plane. The convexity varies considerably, the radius ranging from 5 to 15 mm. The long axes of fossa and tubercle are directed medially and slightly posteriorly. The articular surface of the mandibular head is, approximately, part of a cylinder the axis of which is placed in the same direction as that of the articular surfaces on the temporal bone. The articulating parts of the temporomandibular joint are covered by a fibrous or fibrocartilaginous tissue and not by hyaline cartilage, as in most other articulations of the human body. The

hyaline cartilage in the mandibular condyle which is present during its growth period does not reach the surface.

The articular disc is an oval fibrous plate which is united around its margin with the articular capsule (Fig. 252). It separates the articular space into two compartments: a lower, between condyle and disc, and an upper, between disc and temporal bone. The disc appears biconcave in sagittal section. Its central part is thin, in rare cases perforated; the anterior and especially the posterior borders are thickened (Fig. 253). Fibers of the external pterygoid muscle are attached to its anterior border. The disc serves to adapt the bony surfaces to each other, especially in a forward position of the mandible when the convex condyle approaches the

aonvex articular tubercle. The disc is, at the same time, the movable socket for the mandibular head.

First draft submitted by Donald A; Kerr.

The articular capsule consists of an outer fibrous sac which is loose. It IS strengthened on its lateral side by the temporomandibular ligament.‘

The inner synovial membrane is divided like the articular space. The superior part reaches from the margin of the articular surfaces on the tem poral bone to the disc; the inferior extends from the disc to the neck of the mandible.

2. Histology

The condyle of the mandible is composed of typical cancellous bone Bony covered by a thin layer of compact bone (Fig. 253). The trabeculae are smmm

grouped in such a way that they radiate from the neck of the condyle and

Fig. 252.—Sagitta1 section through the temporomandibular joint. (Courtesy W. Bauer,‘ St. Louis University School oi‘. Dentistry.)

Fig. 253.—Sagitta1 section through the temporomandibular joint of a 28-year-old man. (Courtesy S. W. Chase. Western Reserve University.)

reach the cortex at right angles, thus giving maximal strength to the condylar bone While still maintaining a light construction. In young

individuals the trabeculae are thin and may contain islands of hyaline cartilage near the surface (Fig. 254, A). In older individuals these car

Fig. 254. Sections through the mandibular head. A. Newborn infant. R. Young adult.

tilaginous islands are resorbed and replaced by bone (Fig. 254, B). The marrow spaces are large at first, but decrease in size with progressing age by a marked thickening of the trabeculae. The marrow in the condyle is of the myeloid or cellular type; in older individuals it is sometimes replaced by fatty marrow.

In young individuals the bone of the condyle is capped by a layer of hyaline cartilage which develops as a secondary growth center in three-month-old embryos. It is interposed between the fibrocartilage and the bone. It may still be present in the jaw of a person in his twenties (Fig. 254). The cartilage grows interstitially and by apposition from the deepest layer of the covering fibrous tissue; at the same time it is, gradually, replaced by bone on its inner surface.

Fig. 255.—Higher magnification of part of the mandibular condyle of Fig. 253.

The bone of the mandibular fossa varies considerably from that of the articular tubercle (Fig. 253). In the fossa it consists of a thin compact layer; the articular tubercle is composed of spongy bone covered with a thin layer of compact bone. In rare cases islands of hyaline cartilage are found in the articular tubercle.

The condyle as well as the articular fossa and tubercle are covered by a rather thick layer of fibrous tissue containing a. variable number of cartilage cells. The fibrous or fibrocartilaginous covering of the mandibular condyle is of fairly even thickness (Fig. 255). Its superficial layers consist of a network of strong collagenous fibers. Cartilage cells or chondrocytes may be present and have a tendency to increase in number with age. They can be recognized by their thin capsule which stains heavily with basic dyes. The deepest layer of the fibrocartilage is rich in chondroid cells as long as hyaline cartilage is present in the condyle; it contains only a few thin collagenous fibers. In this zone the appositional growth of the hyaline cartilage of the condyle takes place.

The fibrous layer covering the articulating surface of the temporal bone (Fig, 256) is thin in the articular fossa and thickens rapidly on the posterior slope of the articular tubercle (Fig. 253). In this region the fibrous tissue shows a definite arrangement in two layers, with a small transitional zone between them; the two layers are characterized by the different course of the constituent fibrous bundles. In the inner zone the fibers are at right angles to the bony surface; in the outer zone they run parallel to that surface. As in the fibrous covering of the mandibular condyle, a variable amount of chondrocytes is also found in the tissue on the temporal surface. In adults the deepest layer shows a thin zone of

Fig. 256.—Higher magnification of articular tubercle of Fig. 253

There is no continuous cellular lining on the free surface of the fibrocartilage. Only isolated fibroblasts are situated on the surface itself; they are, generally, characterized by the formation of long flat cytoplasmic processes.

In young individuals the articular disc is composed of dense fibrous tissue which resembles a ligament because the fibers are straight and tightly packed (Fig. 257). Elastic fibers are found throughout the disc, but only in relatively small numbers. The fibroblasts in the disc are elongated and send flat cytoplasmic wing-like processes into the interstices between the adjacent bundles. The mandibular disc does not show the usual fibrocartilaginous character of other interarticular discs. This may be regarded as a functional adaptation to the high mobility and plasticity of this disc.

Fig. 257. -Higher magnification of articular disc of Fig. 253.

With advancing age some of the fibroblasts develop into chondroid cells Which, later, may become real chondrocytes. Even small islands of hyaline cartilage may be found in the discs of older persons. Chondroid cells, true cartilage cells and hyaline ground substance develop in situ by difierentiation of the fibroblasts. In the disc as well as in the fibrous tissue covering the articular surfaces, this cellular change seems to be dependent upon mechanical influences. The presence of chondrocytes increases the resistance and resilience of the fibrous tissue.

As in all other joints, the articular capsule consists of an outer fibrous layer which is strengthened on the lateral surface to form the temporamandibular ligament. The other parts of the fibrous capsule are thin and loose. The inner or synovial layer is a thin layer of connective tissue.

'It contains numerous blood vessels which form a capillary network close «to its inner surface. In many places larger and smaller folds or finger like processes, synovial folds and villi protrude into the articular cavity (Fig. 258). The former concept of a continuous cellular covering of the free synovial surface has been abandoned. Only a few fibroblasts of the synovial membrane reach the surface and, with some histiocyte and lymphatic‘ wandering cells, form an incomplete lining of the synovial membrane.

Fig 258. Villi on the synovial capsule of ternporomandibular joint.

A small amount of viscous fluid, synovial fluid, is found in the articular spaces. It is a lubricant and also a nutrient to the avascular coverings of the bones and to the disc. Its origin is not clearly established. It is possibly in part derived from the liquefied detritus of the most superficial elements of the articulating surfaces. It is not clear whether it is a product of filtration from the blood vessels or a secretion of the cells of the synovial membrane; possibly it is both. TEMPOROMANDJBULAR JOINT ' 331

3. Clinical Considerations

The thinness of the bone in the articular fossa is responsible for fractures if the mandibular head is driven into the fossa by a heavy blow. In such cases injuries of the dura mater and the brain have been reported.

The finer structure of the bone and its fibrocartilaginous covering depends upon mechanical influences. A change in force or direction of stress, occurring especially after loss of posterior teeth, will cause structural changes. These are brought about by resorption and apposition of bone, and by degeneration and reorganization of fibers in the covering of the articulating surfaces and in the disc.“

There is considerable literature on the disturbances after loss of teeth or tooth substance due to changes in the mandibular articulation.“ The clinical symptoms are said to be: impaired hearing, tinnitus (ear buzzing), pain localized to the temporomandibular joint or irradiating into the region of ear or tongue. Many explanations have been advanced for these variable symptoms: pressure on the external auditory meatus exerted by the mandibular condyle which is driven deeply into the articular fossa; compression of the auriculotemporal nerve; compression of the chorda tympani; compression of the auditory tube; impaired function of the tensor palati muscle. Anatomical findings do not substantiate any one of these explanations. Probably, all the diverse symptoms are but consequences of a traumatic arthritis in the mandibular joint.“ 2 It is caused by an increase and a change in direction of the forces of the masticatory muscles upon the structures of the joint.

References

1. Bauer, W.: Anatomische und mikroskopische Untersuchungen iiber das Kiefergelenk Anatomical and Microscopic Investigations on the Temporo-Mandibular oint), Ztschr. f. Stomatol. 80: 1136, 1932.

2. Bauer, W. H.: Osteo-Arthritis Deformans of the Temporo-Mandibular Joint, Am. J. Path. 17: 129, 1941.

3. Baecker, B.: Zur Histologie des Kiefergelenkmeniskus deg Menschen und der

Siiu er (Histology of the Temporo-Mandibular Disc in Man and Mammals), Zts . f. mikr.-anat. For-sch. 26: 223, 1931.

Breitner, 0.: Bone Changes Resulting From Experimental Orthodontic Treatment, Am. J. Orthodont. 26: 521 1940.

Cabrini, R., ‘and Erausquin, La. Articulacion Temporomaxilar de la Rata (Temporo-Mandibular Joint of the Rat), Rev. Odont. de Buenos Aires, 1941.

Cowdry, E. V.: Special Cytology, ed. 2, New York, 1932, Paul B. Hoeber, Inc., pp. 981-989, 1055-1075.

Hammer, J. Aug.: Ueber den feineren Bau der Gelenke (The Microscopic Architecture of the Joints), Arch. f. mikr. Anat. 43: 266, 1894.

Marquart, W.: Zur Histologie der Synovialmembran (Histology of the Synovial Membrane), Ztschr. f. Zellforsch. u. mikr. Anat. 12: 34, 1931.

Peterson, H.: Die Organe des Skeletsystems (Organs of the Skeletal System), Moel1endorf’s Handb. d. mikr. Anat. d. Menschen. Book 2, Part 2, Berlin, 1930, Julius Springer.

10. Schaefler, J. P.: Morris’ Human Anatomy, ed. 10, Philadelphia, 1942, The

Blakiston Co.

11. Schafler, J.: Ueber den feineren Bau und die Entwicklung dos Knorpelgewebes und iiber verwandte Formen der Stiitzsubstanz (On the Microscopic Structure and Development of Cartilage and Related Forms of Supporting Tissue), Ztschr. f. wissensch. Zoo]. 80: 155, 1905.

12. Schaffet, J.: Die Stiitzgewebe (Supporting Tissues), Moe11endorf’s Handb. f. mikr. Anat. d. Menschen, Book 2, Part 2, Berlin, 1930, Julius Springer.

13. Shapiro, H. IL, and Ti-uex, R. 0.: The Temporo-Mandibular Joint and the Auditory Function, J. A. D. A. 30: 1147 1943.

14. Sicher, Harry: Temporomandibufar Articulation in Mandibular Overclosure, J. A. D. A. 36: 131, 1948.

15. Sicher, Harry: Some Aspects of the Anatomy and Pathology of the Temporamandibular Articulation, New York State D. J. 14: 451, 1948.

16. Steinhardt Gr.: Die Beanspruchun der Gelenkfliichen bei versehiedenen Bissarten ( vestigations on the tresses in the Mandibular Articulation and Their Structural Consequences), Deutsche Zahnh. in Vortr. 91: 1, 1934.

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