Development of the human temporomandibular joint

A great deal of research has been published on the development of the human temporomandibular joint (TMJ). However, there is some discordance about its morphological timing. The most controversial aspects concern the moment of the initial organization of the condyle and the squamous part of the temporal bone, the articular disc and capsule and also the cavitation and onset of condylar chondrogenesis. Serial sections of 70 human specimens between weeks 7 and 17 of development were studied by optical microscopy (25 embryos and 45 fetuses). All specimens were obtained from collections of the Institute of Embryology of the Complutense University of Madrid and the Department of Morphological Sciences of the University of Granada. Three phases in the development of the TMJ were identified. The first is the blastematic stage (weeks 7–8 of development), which corresponds with the onset of the organization of the condyle and the articular disc and capsule. During week 8 intramembranous ossification of the temporal squamous bone begins. The second stage is the cavitation stage (weeks 9–11 of development), corresponding to the initial formation of the inferior joint cavity (week 9) and the start condylar chondrogenesis. Week 11 marks the initiation of organization of the superior joint cavity. And the third stage is the maturation stage (after week 12 of development). This work establishes three phases in TMJ development: 1) the blastematic stage (weeks 7–8 of development); 2) the cavitation stage (weeks 9–11 of development); and 3) the maturation stage (after week 12 of development). This study identifies the critical period of TMJ morphogenesis as occurring between weeks 7 and 11 of development. Anat Rec 255:20–33, 1999. © 1999 Wiley‐Liss, Inc.     

Development of nerve fibres in the temporomandibular joint of the human fetus

The development of nerve fibres in the temporomandibular joint (TMJ) in relation to the development of bone, muscle and fibre components was investigated in human fetuses ranging from 9 weeks of gestation to birth. Immunohistochemistry for the glia-associated protein S-100 and for the neuro-specific marker protein gene product 9.5 (PGP 9.5) were used; specimens were compared to specimens of adult TMJ capsule and disc. At 9–10 weeks, a small number of neural elements are already present in the connective tissue around the joint and in the mesenchyme between the two articular blastemas from which the disc will differentiate. By 19 weeks many nerve fibres are clearly visible. Immunohistochemical results suggest diffuse disc innervation extending along the entire disc but not in the thin central area. More complex structures, i.e. encapsulated corpuscles, were also seen. The fetal disc appears highly innervated compared to adult tissue; already at this developmental stage morphology and distribution of nerves and corpuscles in the joint capsule are comparable to those in the adult joint. It may be concluded that the innervation of the TMJ is detectable from the end of the second month and that it develops fully between the third and the fifth month of gestation. Nerve endings in the disc are most numerous at 20 weeks, after which a progressive reduction, possibly secondary to the growth of articular tissues, is observed throughout the last trimester of fetal life and into adult life. The innervation of the lateral pterygoid muscle, on the contrary, is much less than that seen in adult muscles, even at full-term.     

Kinematic analysis of the human temporomandibular joint

A kinematic analysis of the temporomandibular joint (TMJ) is developed to determine the range of motion of the mandible during normal opening and during special motions required for arthroscopic surgery. The translation of the mandible is restricted by the constraint of the ligaments. By accounting for the maximum allowable stretch of a ligament, limits of translation are determined for any normal opening angle of the mandible. The present analysis provides information useful in securing the maximum available space for the protrusion of arthroscopic instruments during TMJ surgery.     

The postnatal development of the human temporomandibular joint

Fifty-one temporomandibular joints (24 male, 27 female) obtained at autopsy were used in the study. Forty-four specimens were younger than ten years while others ranged to 21 years. These joints were radiographed, sectioned sagittally or frontally, and slide-mounted as decalcified and undecalcified sections using conventional histologic techniques. The slides were examined microscopically in whole, polarized, and ultraviolet light. Two of the specimens surveyed exhibited fluorescent labeling as a consequence of therapeutic tetra cycline application. Throughout the postnatal developmental period the articular tissue and disc consist of fibrous connective tissue. Cartilage cells were not observed in these structures at any time during the twenty-one year age-span studied. At birth the disc is flat and develops an accentuated S-shaped profile as the articular tubercle develops. The articular tubercle is only a small elevation at birth and is formed by a combination of endochondral, immature, and ordinary intramembranous bone formation. The characteristic profile of the temporal portion of the joint is achieved during the first two or three years of life, after which gradual enlargement and compaction of bony structures occur. While the mandibular condyle grows in a constant posterior, superior, and lateral direction, it does not attain its mature contour until the late mixed dentition age. Condylar growth cartilage is approximately 1.5 mm thick at birth but it thins down in a short time to about 0.5 mm. During the first two years of life the growth cartilage is penetrated by vascularized connective tissue septa whose function appears to be nourishment of the cartilage. The growth cartilage does not show the columnar arrangement of chondrocytes seen in epiphyses, nor are isogenous groups observed. At 16 to 17 years, the growth cartilage becomes thinner and a closing plate of bone is beginning to coalesce below it.     

The function of the disco-muscular apparatus in the human temporomandibular joint.

The morphology and function of the disco-muscular apparatus of the human TMJ is a controversial subject. Connections between the muscles which move the mandible and the "disco-capsular complex" have been described in a contradictory way. The disco-muscular apparatus is also described as being more extensive than that of the M. pterygoideus alone to include to the Mm. temporalis and masseter. However, the involvement of the latter is considered to be a peripheral variation of the normal anatomy and of little, if any, functional significance. The existence of independent relationships between the deep portions of the masseter and temporal muscles and the disco-capsular apparatus of the human TMJ is rarely discussed or explained. The morphologic findings were derived from fixed and unfixed human temporomandibular joints (TMJ) of varying ages and both sexes, whereby the functional maturity of the masticatory apparatus was taken into consideration. The results of the study show that aside from fibers originating from the superior venter of the M. pterygoideus lateralis, additional muscle or connective tissue fibers from the perimysium of the M. masseter are inserted to varying extents into the disc. The same is true for the M. temporalis, which is also directly connected to the disc via muscular or fibrous elements, or indirectly via fibers from the M. masseter. The insertion of the M. pterygoideus lateralis is always in the medial portion of the Discus articularis and those of the Mm. temporalis and masseter in the middle and lateral portions of the disc respectively. It is highly probable that a direct force transfer through the Mm. temporalis and masseter to the articular disc takes place, and that these muscles contribute to the movement of the disc during jaw movement, whereas the size and form of the muscle insertions are subject to a great deal of individual variation.     

The human temporomandibular joint region in different positions of the mandible.

The anatomy of the human temporomandibular joint region has been investigated mainly under the conditions of dental occlusion. The aim of the present study was to elucidate the topographical situations in other functional positions such as wide-open mouth, protrusion and lateral displacement. The respective mouth positions were adjusted before fixation and controlled by magnetic resonance tomography. The temporomandibular joint regions were embedded in epoxy resin, and cut serially in the sagittal or the frontal plane. WIDE OPEN MOUTH: The articular disc lies with its intermediate zone between the articular tubercle and the dorsal convexity of the condylar process, and thus adapts the articulating surfaces of the bones perfectly to each other. Massive enlargement of the retroarticular cushion is seen, whereas the loss connective tissue on the anterior side of the joint appears completely compressed. PROTRUSION: The disc lies with its intermediate zone between the convexities of the condylar process and the articular eminence. On the lateral side it appears to be compressed between mandible and temporal bone. The retroarticular cushion is moderately enlarged. The anterior compartment of loose connective tissue is smaller than in occlusion. LATERAL DISPLACEMENT: On the working side the articular disc is in a stabilized position between the bony joint elements. The balancing condyle is in a protruded position with the retroarticular cushion reaching into the dorso-lateral half of the mandibular fossa. CONCLUSION: Protrusion appears as the position with the highest mechanical stress upon the articular disc.     

Dynamics modeling of human temporomandibular joint during whiplash

The objective of this study is to simulate the dynamic response of the temporomandibular joint forces within a rear-end impacted vehicle. Clinicians reports symptoms of temporomandibular joint disorders in many patients who have experienced vehicle rear-end impacts. In rear-end impact, a vehicle occupant's head is thrust rearward with respect to the vehicle in a whiplash action. During this motion, complex dynamic forces act on the jaw bone. To understand the dynamic forces acting on the jaw, we extended an existing human head/neck model by adding a movable jaw, and performed simulation of the jaw motions during rear-end impacts at 4.2, 6.4 and 9.6 m/s. Results predicted temporomandibular joint torques, relative angle between the head and jaw, jaw angular acceleration and linear acceleration of the jaw's center of mass.     

Aspects of morphology and guidance of the human temporomandibular joint

Examinations of the curvature morphology of the temporomandibular joints (TMJs) in macerated human skulls yielded that in initial protrusive cranial border motion, parts of the condylar articulating surfaces are only functional under force transmission. These areas were found on the lateral-central side of the condyle. In contrast to the Cercopithecus mona, a monkey species, the human TMJ apparently possesses a distinctly higher spatial performance range.     

On the formation of the temporomandibular joint cavity in the human fetus

The purpose of this study was to clarify the mechanism of articular cavity formation by means of observing the temporomandibular joint (TMJ) in human fetuses (9th-30th gestational weeks) using light microscope. In the 9th-11th week, although neither cavity had been formed, several small blood vessels running postero-anteriorly on the lower surface of the articular disk that would be the future lower cavity were recognized. However, such blood vessels were not seen in the future upper cavity beneath the glenoid fossa. In the 12th week, when the lower cavity formation commenced, the cavity was filled with blood corpuscles, and a series of apertures was observed throughout the condyle, from the posterior portion to a part of the anterior portion. Tracing posteriorly, the lower cavity diminished gradually until it had at last united to one blood vessel. On the other hand, in upper cavity formation, which was recognized only at the posterior portion of the TMJ, no blood corpuscles were seen in the upper cavity but several small clusters of collagen fibers. Blood corpuscles in the lower cavity disappeared after the formation of synovial membrane (20th week) and vascular canals in the condyle (21st week). From these findings, the mechanism of lower cavity formation appears to differ from that of upper cavity formation. Lower cavity formation involved small blood vessels running postero-anteriorly on the lower surface of the articular disk. As for upper cavitation, there was no evidence of blood vessels, which would suggest that upper cavitation depends on another mechanism of formation.     

A new retinacular ligament and vein of the human temporomandibular joint

In the human temporomandibular joints of 14 Japanese cadavers, we observed a new retinacular ligament that connected to the retrodiskal pad posterolaterally and was accompanied by a vein draining the retrodiskal pad. This retinacular ligament originated from lateral to posterolateral part of the joint. The origin included the articular tubercle of the zygomatic process of the temporal bone. The ligament descended along the mandibular ramus to insert into the fascia of the masseter muscle at the mandibular angle. The vein originated from the venous plexus in the retrodiskal pad and ran parallel to the retinacular ligament, giving off branches to the retromandibular, transverse facial, and superfacial temporal veins. There were no remarkable differences in the size of the retinacular ligaments among individuals as well as between the left and right sides. The retinacular ligament had firm fibrous connections with the posterolateral part of the retrodiskal pad, where the external fibrous membrane of the articular capsule was lacking. These findings suggest that the retinacular ligament and its accompanying vein function together to maintain blood circulation during jaw movement and may also be related to the development of occlusal disorders. © 1995 WiIey-Liss, Inc.     

Adjuvant-induced arthritis in the temporomandibular joint of rats.

When Lewis rats were immunized by intradermal injection into the parietal scalp rather than into the footpad with mycobacterial delipidated cells in squalene, arthritis could be produced in the temporomandibular joint (TMJ) with a maximum incidence of 60%, accompanied by systemic polyarthritis. Other methods of immunization including intradermal injection into the tail, posterior cervical region, or intra-inguinal lymph nodes did not induce arthritis in the TMJ. A combination of this inoculation and hemiocclusal loss markedly increased the incidence of arthritis in the TMJ. This arthritis in the TMJ was, however, milder than that in other joints and was apparent only histologically. The group given intradermal injection of adjuvants into the parietal scalp showed definite suppression of body weight gain. Since the method of intradermal injection into the parietal scalp can induce a high incidence of arthritis in the TMJ, our study presents a unique experimental model for study of arthritis in the TMJ.     

Functional anatomy of the temporomandibular joint

Summary A study of 72 temporomandibular joints of adults without any gross signs of degenerative changes was made, in order to analyse the stress on individual regions of the joint, and to determine the path of the split line pattern in the articular cartilage. The cancellous architecture and the material distribution in the juxta-articular bone were also investigated. Zones of high-density compact substance in the lateral region of the joint, and the presence of attractive singular points in the split line orientation in this localization, suggest great stress on the lateral part of the temporomandibular joint. This increased stress in the lateral region is confirmed by the fact that arthrotic changes in the temporomandibular joint first almost always appear laterally. Degenerative changes usually originate at the articular disc, affect the articular tubercle after a delay, and finally spread to the condyle. Besides the greater physiological, mechanical stress on the lateral region of the joint, the force acting on every individual temporomandibular joint is influenced by the dental condition. The molars and bicuspids serving as a support zone play a decisive role in this context.Dedicated to Professor Dr. H. Haug on the occasion of his 70th birthday     

Remarks on the morphology of the human temporomandibular joint in the fetal period

Skeletons of human fetuses of different ages allow the study of the considerable transformations of the mandibular joint and the mandible in this relative short stage of life. The condyle is anchored in the mandible by a conical process. The tip of this cone extends to the anLage of the 2nd milk molar. The conical process can be recognized macroscopically up to newborn age. It can also be identified by modern imaging methods. The cone can be well distinguished from the surrounding bone of the mandible. The mandibular joints of fetuses in the 31st, the 32nd, the 39th week and of a newborn were dissected, removed, and histologically investigated. The conical process of the condyle was clearly observed. The cartilage on the condyle is characterised by a layered structure which is typical for a center of growth. In the cartilage of young fetuses, blood vessels were found, reaching from the trabecular bone to the articular space. At this stage of life, blood vessels are also present in the central part of the discus articularis.     

Dynamic 3D FE modelling of the human temporomandibular joint during whiplash

Rear-end impacts account for more than one-third of vehicle accidents, and nearly 40% of these accidents produce whiplash injuries. Whiplash injury to the neck has often been considered a significant risk factor for the development of temporomandibular disorders (TMD). The objective of this study was to simulate the dynamic response of the temporomandibular joint during two types of impacts: a rear end and a frontal impact. To understand the dynamic forces acting on the joint, we extended a previous human temporomandibular joint model and analyzed the stress distributions in the soft elements of the joint. In the rear-end impact, it could be appreciated that the inertia of the mandible caused it to move posteriorly slower than the head, and this resulted in downward and forward displacements of the disc-condyle complex relative to the cranial base. Consequently, a rapid and big mouth opening occurs. In contrast, during the frontal impact, the mouth hardly opened, because the superior maxilla pushed the mandible to move together. There was not differential movement between bony components of the joint and therefore the soft tissues of the joint were not subjected to high loads. From these results, and despite the limitations of the simulations performed, we could conclude that neither a rear-end impact at low-velocity nor a frontal impact would produce damage to the soft tissues of the joint.     

Application of bromodeoxyuridine immunohistochemistry to the rat temporomandibular joint.

To detect S-phase cells in the decalcified paraffin-embedded temporomandibular joint (TMJ) tissues of the rat, bromodeoxyuridine (BrdUrd) immunohistochemistry was performed. Percardiac perfusion of 10% EDTA-2Na Tris buffer accelerated the decalcification. The use of the monoclonal antibody to BrdUrd enabled the visualization of the distribution of S-phase cells. This method is practical in studying cell kinetics and the specific proliferation mode of the TMJ.     

Tensile stress patterns predicted in the articular disc of the human temporomandibular joint

The direction of the first principal stress in the articular disc of the temporomandibular joint was predicted with a biomechanical model of the human masticatory system. The results were compared with the orientation of its collagen fibers. Furthermore, the effect of an active pull of the superior lateral pterygoid muscle, which is directly attached to the articular disc, was studied. It was hypothesized that the markedly antero-posterior direction of the collagen fibers would be reflected in the direction of the tensile stresses in the disc and that active pull of the superior lateral pterygoid muscle would augment these tensions. It was found that the tensile patterns were extremely dependent on the stage of movement and on the mandibular position. They differed between the superior and inferior layers of the disc. The hypothesis could only be confirmed for the anterior and middle portions of the disc. The predicted tensile principal stresses in the posterior part of the disc alternated between antero-posterior and medio-lateral directions.     

Factors affecting the variation in the adult temporomandibular joint of archaeological human populations

To elucidate factors that may affect the variation in the bony components of temporomandibular joint (TMJ), a preliminary study was conducted on the temporal articular surface of the TMJ of 30 skulls from Iron Age and medieval populations from Lithuania and a mixed Neolithic and Bronze Age population from the Central Elbe-Saale region (CESR). Using three-dimensional (3D) photos of the skulls, length and width measurements of the TMJ were obtained and compared with external skull measurements. Distinct, random variation between the TMJ values from opposite sides of the cranium were identified as fluctuating asymmetry. ANOVA results suggest significant differences in the length of the TMJ between the population of the CESR and the two Lithuanian populations, but not between the two Lithuanian populations. Environmental factors, including geography, may be responsible for the variation in the TMJ form.