Comparison of knee joint and temporomandibular joint development in pig embryos

Although the knee joint (KNJ) and temporomandibular joint (TMJ) all belong to the synovial joint, there are many differences in developmental origin, joint structure and articular cartilage type. Studies of joint development in embryos have been performed, mainly using poultry and rodents. However, KNJ and TMJ in poultry and rodents differ from those in humans in several ways. Very little work has been done on the embryonic development of KNJ and TMJ in large mammals. Several studies have shown that pigs are ideal animals for embryonic development research. Embryonic day 30 (E30), E35, E45, E55, E75, E90, Postnatal day 0 (P0) and Postnatal day 30 (P30) embryos/fetuses from the pigs were used for this study. The results showed that KNJ develops earlier than TMJ. Only one mesenchymal condensate of KNJ is formed on E30, while two mesenchymal condensates of TMJ are present on E35. All structures of KNJ and TMJ were formed on E45. The growth plate of KNJ begins to develop on E45 and becomes more pronounced from E55 to P30. From E75 to E90, more and more vascular-rich cartilage canals form in the cartilage regions of both joints. The cartilaginous canal of the TMJ divides the condyle into sections along the longitudinal axis of the condyle. This arrangement of cartilaginous canal was not found in the KNJ. The chondrification of KNJ precedes that of TMJ. Ossification of the knee condyle occurs gradually from the middle to the periphery, while that of the TMJ occurs gradually from the base of the mandibular condyle. In the KNJ, the ossification of the articular condyle is evident from P0 to P30, and the growth plate is completely formed on P30. In the TMJ, the cartilage layer of condyle becomes thinner from P0 to P30. There is no growth plate formation in TMJ during its entire development. There is no growth plate formation in the TMJ throughout its development. The condyle may be the developmental center of the TMJ. The chondrocytes and hypertrophic chondrocytes of the growth plate are densely arranged. The condylar chondrocytes of TMJ are scattered, while the hypertrophic chondrocytes are arranged. Embryonic development of KNJ and TMJ in pigs is an important bridge for translating the results of rodent studies to medical applications.

Part I: Development and Physiology of the Temporomandibular Joint

PURPOSE OF REVIEW

Investigate the developmental physiology of the temporomandibular joint (TMJ), a unique articulation between the cranium and the mandible.

RECENT FINDINGS

Principal regulatory factors for TMJ and disc development are Indian hedgehog (IHH) and bone morphogenetic protein (BMP-2). The mechanism is closely associated with ear morphogenesis. Secondary condylar cartilage emerges as a subperiosteal blastema on the medial surface of the posterior mandible. The condylar articular surface is immunoreactive for tenascin-C, so it is a modified fibrous periosteum with an underlying proliferative zone (cambrium layer) that differentiates into fibrocartilage. The latter cushions high loads and subsequently produces endochondral bone. The TMJ is a heavily loaded joint with three cushioning layers of fibrocartilage in the disc, as well as in subarticular zones in the fossa and mandibular condyle. The periosteal articular surface produces fibrocartilage to resist heavy loads, and has unique healing and adaptive properties for maintaining life support functions under adverse environmental conditions.

Comparative analysis of the structure of temporomandibular joint in human and rabbit

In order to increase knowledge on the morphology and structure of the articular disc of the TMJ for a better understanding of the functional role of the same, it proceeded with an investigation on histological samples in the block of 'TMJ and periarticular tissues of adult rabbits and human fetuses at different stage of development.

Human temporomandibular joint morphogenesis

Temporomandibular joint morphogenesis was studied. Ranging in age of fetuses examined was from 6 to14 weeks' gestation. Our results showed the condyle so first element that appear between 6 degrees and 8 degrees week (condylar blastema). After a week appear temporal elements. Disk appear at the same time of glenoid blastema and it reaches an advanced differentation before of the condyle and temporal element, so these don't effect machanical compression on mesenchyma where we find the disk. So we think that the disk result of genetic expression and it isn't the result of mechanical compression. The inferior joint cavity appear to 12 week. The superior joint cavity appear to 13-14 week. In conclusion, the appearance of the condyle is the first event during TMJ morphogenesis, with its initial bud, in form of a mesenchymal thickening, becoming detectable between the sixth and eight week of development, when all the large joints of the limbs are already well defined.

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.

Fetal jaw movement affects development of articular disk in the temporomandibular joint

Previous studies suggest that jaw movement is an important factor in the development of cartilage in the temporomandibular joint during the prenatal and postnatal periods. In the present study, the effects of fetal jaw movement on the articular disk were studied in mice by restraining the opening movement of the mouth using the mouse exo utero development system. At embryonic day 18.5, the articular disk was reduced in size in the embryos whose maxilla and mandible were sutured (sutured group) and there were changes in the cellular morphology of the mesenchymal cells in the disk. The volume of the articular disk, the total number of cells and the number of 5-bromo-2'-deoxyuridine-positive cells in the articular disk were significantly lower in the sutured group than in the non-sutured control group. Our data revealed that fetal jaw movement affects the development of the articular disk in the temporomandibular joint.

Alteration of BMP-4 and Runx2 expression patterns in mouse temporomandibular joint after ovariectomy

OBJECTIVE

Temporomandibular disorder (TMD) includes a number of clinical conditions involving the masticatory musculature or the temporomandibular joint (TMJ) and associated structures. Previous studies have shown the presence of high-affinity estrogen receptors in the TMJ articular cartilage. The aim of this study was to evaluate the developmental changes in mouse TMJ under estrogen deficiency.

MATERIALS AND METHODS

Four-month-old ovariectomized mice were killed after certain weeks. We examined the significant alterations of the expression patterns of bone morphogenetic protein (BMP)-4, Runx2, and bone sialoprotein (BSP) after ovariectomy.

RESULTS

In the control group, BMP-4, Runx2, and BSP expressions showed no definite difference at any stage. In the ovariectomy group, the intensity of BMP-4 and Runx2 expression increased after ovariectomy. BSP immunoreactivity, however, increased slightly at 2 weeks but then decreased gradually.

CONCLUSIONS

Estrogen plays important roles in the metabolism and maintenance of TMJ via regulations of signaling molecules such as BMP-4, Runx2, and BSP. Our results suggest that estrogen deficiency is a candidate cause of TMD. This study revealed further osteogenetic properties of estrogen that may be useful in the clinical treatment and prevention of TMD.

Temporomandibular joint formation and condyle growth require Indian hedgehog signaling

The temporomandibular joint (TMJ) is essential for jaw function, but the mechanisms regulating its development remain poorly understood. Because Indian hedgehog (Ihh) regulates trunk and limb skeletogenesis, we studied its possible roles in TMJ development. In wild-type mouse embryos, Ihh expression was already strong in condylar cartilage by embryonic day (E) 15.5, and expression of Ihh receptors and effector genes (Gli1, Gli2, Gli3, and PTHrP) indicated that Ihh range of action normally reached apical condylar tissue layers, including polymorphic chondroprogenitor layer and articular disc primordia. In Ihh(-/-) embryos, TMJ development was severely compromised. Condylar cartilage growth, polymorphic cell proliferation, and PTHrP expression were all inhibited, and growth plate organization and chondrocyte gene expression patterns were abnormal. These severe defects were partially corrected in double Ihh(-/-)/Gli3(-/-) mutants, signifying that Ihh action is normally modulated and delimited by Gli3 and Gli3(R) in particular. Both single and double mutants, however, failed to form an articular disc primordium, normally appreciable as an independent condensation between condylar apex and neighboring developing temporal bone in wild-type. This failure persisted at later stages, leading to complete absence of a normal functional disc and lubricin-expressing joint cavities. In summary, Ihh is very important for TMJ development, where it appears to regulate growth and elongation events, condylar cartilage phenotype, and chondroprogenitor cell function. Absence of articular disc and joint cavities in single and double mutants points to irreplaceable Ihh roles in formation of those critical TMJ components.

Osteoprotegerin (OPG) and RANKL expression and distribution in developing human craniomandibular joint

During embryogenesis the bone tissue of craniomandibular joint (CMJ) is formed through two pathways: intramembranous ossification and endochondral ossification. The development process is under the control of regulatory factors. The osteoprotegerin (OPG) and the receptor activator of nuclear factor (NF)-kappaB ligand are key regulators of osteoclastogenesis. The aim of this study is the localization of OPG and RANKL mRNA and protein in the foetal CMJ by immunohistochemistry (IHC) and in situ hybridization (ISH). The main results were: OPG and RANKL mRNA and protein were co-localized in the same cell types; OPG and RANKL were specially immunolocated in osteogenic cells; immunolabeling was often seen in the nucleus and cytoplasm of otherwise negative hypertrophic chondrocytes; IHC and ISH labeling decreased from proliferative to hypertrophic chondrocytes; early osteocytes showed dual protein expression and some of the mature osteocytes were ISH-negative; periosteal osteoclasts and chondroclasts were mostly stained by IHC and variably labeled by ISH; the new bone matrix and trabecular borders showed intense immunolabeling. The co-expression of OPG and RANKL in the same bone cell types confirms their strictly coupled action in the regulation of bone metabolism in the CMJ development and their extracellular presence in the new bone matrix and trabecular borders suggests a local regulatory role.

Embryological study of the development of the rat temporomandibular joint: highlighting the development of the glenoid fossa

Basic embryological findings on the development of the temporomandibular joint have yet to be elucidated sufficiently. This experiment, was undertaken to find the standard time course of the development of the temporomandibular joint in rat fetuses. Serial frontal and sagittal sections of rat fetal heads (between 13.5 and 20.5 days post-conception [p.c.]) were examined microscopically. The condyle was recognized as a mesenchymal condensation at 14.5 days p.c., while the glenoid fossa was recognized at 15.5 days p.c. The mesenchymal condensation of the condyle had differentiated into chondrocytes by 16.5 days p.c., and endochondral ossification was recognized at 17.5 days p.c. The intramembranous ossification of the glenoid fossa was already recognized by 16.5 days p.c.; this started in the posterior region and progressed anteriorly between the zygomatic arch and the squamous part of the temporal bone. Ossification of the condyle had not been completed by 20.5 days p.c., a mass of hypertrophic chondrocytes remained in the center of the condylar head. The glenoid fossa was almost completely ossified by 19.5 days p.c. A coarse region of cells, reminiscent of apoptosis, was recognized in the region of the prospective superior joint space at 17.5 days p.c., and an actual joint space had formed by 18.5 days p.c. The inferior joint space was recognized at 19.5 days p.c. as a fissural cavity, but it was much narrower than its superior counterpart. The prospective meniscus was distinguished on the condylar surface at 17.5 days p.c. by the difference in the shape of its constituent cells. The results obtained here seem to be useful for further experiments and molecular biological studies.

The immunohistochemical approach to determine the origin and possible function of the juxtaoral organ in dogs

OBJECTIVE

In this study, we applied immuno- histochemical techniques on the functionally little known organ of Chievitz (juxtaoral organ [JOO]) in dogs to determine its origin and possible function.

METHODS

The term abortive materials of 6 Doberman dogs were used for experimental procedures in July 2002 to June 2003 at Gazi University Faculty of Medicine, Ankara, Turkey, after routine light microscopic tissue preparation, the sections were stained with Masson's trichrome stain. In order to elucidate the function-related origin of the organ, we used epidermal growth factor (EGF-r), transforming growth factor (TGF-alpha) and nerve growth factor (NGF-beta) immunohistochemical stains.

RESULTS

We observed a very strong and widespread immunoreactivity of EGF-r and TGF-alpha on simple squamous capsular cells. We detected nerve growth factor-beta positivity in granular form both in simple squamous capsular cells and in neighboring connective tissue. However, we did not detect EGF-r reactivity on parenchymal cells except a weak immunoreactivity on central ones. We noticed transforming growth factor-alpha in most of the parenchymal cells while we observed NGF-beta strongly in all the parenchymal cells.

CONCLUSION

These results may point out that the JOO may be of mesothelial or epithelial origin. Having NGF-alpha positive granules and close relationship with blood vessels may imply a neurosecretory function. We believe that our study may add new perspectives to the function of the JOO.

Development of the articular cavity in the rat temporomandibular joint with special reference to the behavior of endothelial cells and macrophages

Previous developmental studies on the temporomandibular joint (TMJ) have proposed several hypotheses on the formation of its articular cavity. However, detailed information is meager. The present study examined the formation process of the articular cavity in the rat TMJ by immunocytochemistry for CD31, RECA-1, and ED1, which are useful cellular markers for endothelial cells and monocyte/macrophage lineages, respectively. The upper articular cavity formation had begun by embryonic day 21 (E21) and was completed at postnatal day 1 (P1) in advance of the lower cavitation; the latter took place from P1 to P3. The occurrence and distribution pattern of the CD31-, RECA-1-, and ED1-positive cells differed between the upper and lower articular cavity-forming areas: the ED1-positive cells exclusively occurred in the area of the prospective upper articular cavity prior to its formation, while no ED1-positive cell appeared in the lower cavity-forming area. In contrast, the CD31- and RECA-1-positive endothelial cells were restricted to the lower cavity-forming area (never the prospective upper cavity) at E19 and diminished thereafter. Throughout the cavity formation, we failed to find any apoptotic cells in the cavity formation area, indicating no involvement of apoptosis in the cavity formation in TMJ. The present findings on the behaviors of endothelial cells and ED1-positive cells show a possibility of different mechanism in the cavity formation between the upper and lower articular cavities in the rat TMJ. The appearance of ED1-reactive cells and temporal vascularization may play crucial roles in the upper and lower articular cavity formation, respectively.

Development of the synovial membrane in the rat temporomandibular joint as demonstrated by immunocytochemistry for heat shock protein 25

The synovial lining layer of the temporomandibular joint (TMJ) consists of macrophage-like type A cells and fibroblast-like type B cells. Until now, little information has been available on the development of the synovial membrane in TMJ. In the present study we examined the development of the synovial lining layer in the rat TMJ by light- and electron-microscopic immunocytochemistry for heat shock protein (Hsp) 25, which is a useful marker for type B cells. At embryonic day 19 (E19), a few Hsp25-positive cells first appeared in the upper portion of the developing condyle. During the formation of the upper articular cavity (E21 to postnatal day 1 (P1)), a few positive cells were arranged on its surface. Immunoelectron microscopy demonstrated that these cells had ultrastructural features of fibroblast-like type B cells. In addition, some Hsp25-positive cells moved to the deep portion by extending their cytoplasmic processes toward the articular cavity at P3. At that time, the presence of typical macrophage-like type A cells in the lining layer was confirmed by immunoelectron microscopy. The slender processes of Hsp25-positive cells showed a continuous covering with the synovial surface at P7, followed by a drastic increase in the Hsp25-positive cells at P15 and later, when active jaw movement occurred. These findings suggested that the arrangement and morphological maturation of type B cells are closely related to the formation of the articular cavity in the embryonic period and the commencement of active jaw movement after birth, respectively.

Synovial membrane in the temporomandibular joint--its morphology, function and development

This paper reviews recent findings of the synovial membrane, in particular the morphology, function and development of synovial lining cells, in the temporomandibular joint (TMJ). Electron microscopic studies have confirmed the synovial membrane in TMJ consists of macrophage-like type A cells and fibroblast-like type B cells identical to those in other systematic joints. The macrophage-like type A cells react with anti-macrophage and macrophage-derived substances including the major histocompatibility class II molecule, and show a drastic increase in their number in the inflamed synovial membrane. In addition, they have the ability to produce substances involved in the progression of TMJ inflammation such as nitric oxide and inducible nitric oxide synthase. Observation of osteopetrotic mice revealed that macrophage-like type A cells in TMJ are derived from monocyte lineage. Immunocytochemistry for 25kDa heat shock protein was able to depict the entire shape of fibroblast-like type B cells including their unique processes. The expression of an estrogen receptor alpha-immunoreaction in the fibroblast-like type B cells may explain the etiology of temporomandibular disorders at a higher frequency in females than in males, suggesting that TMJ is a target tissue for estrogen. Furthermore, fibroblast-like type B cells are equipped with a basement membrane to serve as an adhesion molecule for the fibroblast-like type B cells to keep their epithelial arrangement. A clear understanding of the morphology of the intact synovial membrane will serve to clarify the etiology and development of temporomandibular disorders.

Distribution of tenascin-c and -X in rat TMJ development

In the neonatal and postnatal development of rat TMJ, tenascin-C and -X were detected in the muscle, bone matrix, connective tissue around the bone, and blood vessel of rats at E18 (18-days old embryo), 0-, and 5-days postnatal. The reaction of tenascin-X was also found in the connective tissue around the mandibular condyle. The mRNA of tenascin-C (600 bp) and -X (588 bp) was also detected in the developmental muscle with the level of tenascin-C mRNA moderately decreased during development. Therefore, tenascin-C and -X may have different effects on the connective tissue during development of TMJ.

[The first appearance of Meckel's cartilage in the fetus]

Meckel's cartilage plays an important role in the topographical organisation and in the differentiation of the facial structure during the embryonal and even much later during the foetal period. Our observations on serial sections carried out in two human foetuses aged 12 and 16 weeks indicate that the two dorsal (tympanic) and ventral (mandibular) branches of Meckel's cartilage are perfectly defined at 16 weeks. In the dorsal branch, the primordia of the incus and of head of the malleus are still composed on non-ossified cartilage. In the ventral branch, it is also possible to describe at 16 weeks three posterior, medial and anterior parts which are composed of cartilage. The initiating role played by the ventral part of Meckel's cartilage on the ossification of the mandible leads during the embryonal period to the formation of the mandibular primary growth center, which is therefore clearly defined in our first stage at 12 weeks. The partial fibrous evolution and the regression of the major part of the ventral branch of Meckel's cartilage only start after 16 weeks of intrauterine life.

Computerized 3-dimensional study of the embryologic development of the human masticatory muscles and temporomandibular joint

PURPOSE

In this study, the development of human embryonic temporomandibular joint (TMJ) and masticatory muscles were investigated by using computed 3-dimensional reconstructions.

MATERIALS AND METHODS

Sixteen human embryos and fetuses, ranging from 6.5 to 107 mm crown-rump length, were examined.

RESULTS

At 10 weeks, a band of mesenchyme extending from the attachment of the lateral pterygoid muscle to the condylar process was observed to pass through the medial side of the condylar process to attach to the malleus. The temporal, masseter, and pterygoid muscles develop from the so called "temporal muscle" primordium, and the temporal muscle was in continuity with the masseter muscle until 14 weeks of fetal life.

CONCLUSIONS

The study shows that the muscles of mastication arise from a single primordium. It also confirms the presence of a ligamentous attachment between the lateral pterygoid muscle and the malleus.

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.

[Role of apoptosis and bcl-2 gene in the temporomandibular joint development]

OBJECTIVE

Apoptosis involving in embryogenesis and organ formation has been verified, but the possible roles of apoptosis and its related regulative genes have not been clarified. Temporomandibular joint dysfunction (TMD) has increased in incidence and occurred increasingly in young patients. Thus, research on the development and gene modulation is necessary.

METHODS

Tdt-mediated dUTP nick end labeling (TUNEL) and mRNA in situ hybridization were used in observation of apoptosis and bcl-2 gene expression in TMJ of SD rats during prenatal and postnatal developmental period.

RESULTS

Apoptosis involved in different development periods of condylar cartilage, and the cells of apoptosis mainly located in the proliferative zone and the area between the prehypertrophic zone and the late hypertrophic zone., bcl-2 was expressed in chondrocytes throughout condylar cartilage with high levels in proliferative and prehypertrophic chondrocytes and obvious low levels in the late hypertrophic chondrocytes. Very few matured chondrocytes expressed bcl-2.

CONCLUSION

Apoptosis regulated by bcl-2 plays an important role in prenatal and postnatal development of TMJ.

Development of the human temporomandibular joint

A great deal of research has been published on the development of the human temporomandibularjoint (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.

The vascular relationship between the temporomandibular joint and the middle ear in the human fetus

PURPOSE

The aim of this work was to clarify the vascular relationships between the middle ear and the temporomandibular joint region during human fetal development.

MATERIALS AND METHODS

Light microscopic studies were done on 40 human fetuses from 72 mm crown-rump length (C-R) to 150 mm C-R, which were stained by various methods. Five human fetuses were dissected. Natural latex with industrial coloring was injected through the external carotid artery. All specimens were dissected bilaterally.

RESULTS

The limits of the retroarticular region and the fetal tympanosquamosal fissure are shown. The anterior tympanic artery has a variable origin. In most cases, it originates from the maxillary artery; in other cases it originates from the superficial temporal artery or the bifurcation of the external carotid artery. On its way through the retroarticular region, it gives branches to the posterior part of the temporomandibular joint. It progresses along the most lateral part of the tympanosquamosal fissure, dividing into three branches that extend throughout the middle ear. A number of venous spaces in the retroarticular region that constitute the retrodiscal venous plexus. Small venous vessels along the fetal tympanosquamosal fissure accompany the anterior tympanic artery and drain into the retrodiscal venous plexus.

CONCLUSIONS

During human fetal development, there is a wide connection across the tympanosquamosal fissure between the middle ear and the temporomandibular joint region. The anterior tympanic artery and its branches, as well as small venous vessels that are connected with the retrodiscal venous plexus, extend along the most lateral part of the fissure.

Development of the human temporomandibular joint. Computer-aided 3D-reconstructions

Computer-aided graphical three-dimensional reconstructions of histological serial sections of 12 human embryos and fetuses (25-250 mm Crown-rump length (CRL)) were used to trace the prenatal development of the elements of the human temporomandibular joint. The primordia of the condylar and coronoid processes could be identified as two bony peaks at the dorsal ends of the mandible at the stage of 25 mm CRL. The primordium of the temporal bone already existed at the stage of 37 mm CRL. The bone was apparent with a convex contour towards the condyle. The glenoid fossa was not yet visible. At 65 mm CRL, the osseous glenoid fossa could be distinguished at the enlarged temporal bone formation. The glenoid fossa developed posteriorly and medially from the condyle and extended in cranial and anterior direction. The glenoid fossa had various contours, changing from flat and slightly convex (65 mm CRL) to concave (250 mm CRL) with an articular tubercle. The distance between fossa and condyle increased proportionally. The lower joint cavity appeared at an earlier stage (65 mm CRL) than the upper joint cavity (70 mm CRL). Both cavities started development as isolated compartments fusing later on. The upper joint cavity followed the contour of the fossa, whereas the lower joint cavity followed the form of the condyle. The biconcave shape of the articular disc as well as the attachment of the lateral pterygoid muscle could be observed very early (70 mm CRL).

Attachment of the sphenomandibular ligament to bone during intrauterine embryo development for the control of mandibular movement

The present study examined the relationship between jaw movement and the site of attachment of the sphenomandibular ligament, which is involved in the control of lateral jaw movement. Major fibers of this ligament are attached to the sphenoid spine and the mandibular lingula. During early stages of embryonic development, however, this ligament is not attached to the sphenoid spine. No consensus has yet been reached concerning the time at which this ligament becomes attached to this spine. The present study was performed to resolve this question and to analyze the relationship of this event of jaw movement. Attachment of the sphenomandibular ligament to the sphenoid spine was observed in fetuses at a gestational age of about 8 months (32 weeks). This may be because fetuses undergo functional changes (initiation of jaw movement such as mastication and swallowing) at this gestational age. This finding suggests that the attachment of the sphenomandibular ligament to the sphenoid spine may be related to fetal jaw movements.

[The development and morphofunctional characteristics of the human lateral pterygoid muscle]

Peculiarities of the development of superior and inferior heads of lateral pterygoid muscle (LPM) as well as their micro- and ultramicroscopic structure were studied as related to the temporomandibular joint elements in human fetuses and newborns. As a result, heterogeneity and asynchronism of the development of myogenic elements of certain LPM heads were demonstrated. The process of muscle fibres differentiation in LPM superior head leads to more mature structural organization and runs faster than in the inferior head. By the moment of birth average section area of superior head muscle fibres is significantly higher than the inferior head similar parameter.

Apoptosis in the development of the temporomandibular joint

Apoptosis has been shown to be involved in remodeling of organs during development, and derangement of the apoptotic process may result in temporomandibular joint (TMJ) dysfunction or congenital malformation. To investigate the relationship between the development of the TMJ and apoptosis, rat fetuses at 17.5-20.5 days of gestation (E17.5-20.5, vaginal plug=E0) and rats at postnatal days 1, 2, 3, 5, and 10 (P1, 2, 3, 5, and 10) were examined by light (LM) and transmission electron microscopy (TEM) and electrophoretic analysis of DNA fragmentation. At E17.5 and 18.5, a few layers of slender mesenchymal cells which eventually develop into the TMJ disk were observed, although TEM or electrophoresis did not reveal apoptotic cells at these stages. At E19.5 and 20.5, all structures of the TMJ except the lower joint cavity could be distinguished, but at these stages apoptotic cells were not observed. In P1 condyles, apoptotic cells were observed by TEM both at the subsurface of the condyle and in the region at which the lateral pterygoid muscle attaches to the condyle. These apoptotic cells showed irregular chromatin condensation, convolution of the cell membrane, and fragmentation and disintegration of the cytoplasm. Electrophoretic analysis of the P1 condyle further confirmed DNA fragmentation. Apoptosis was not observed in all specimens at the P1 stage. It was confirmed in 8 out of 20 animals (10 out of 27 joints) by TEM and/or electrophoretic analysis. The shape of the upper portion of the condyle flattened progressively from E20.5 to P2. At this stage, the lower joint cavity was developing, as observed by LM. These findings suggest that the morphological changes of the mandibular condyle effected by apoptosis, together with development of the lower joint cavity, play important roles in the postnatal functional adaptation to external stimuli such as mechanical strain.

Distribution and coexistence of neuropeptides in nerve fibres in the temporomandibular joint of late gestation fetal sheep

The density and distribution of nerve fibres immunoreactive to antisera for PGP 9.5 (general neuronal marker), calcitonin gene related peptide (CGRP) and substance P (SP) (markers for sensory neurons), as well as neuropeptide Y (NPY), vasoactive intestinal peptide (VIP) and tyrosine hydroxylase (TH) (markers for autonomic fibres), were examined in the temporomandibular joint (TMJ) of late gestation fetal sheep. This work formed part of a project investigating the influence of age and osteoarthritis on the innervation of the TMJ, and was undertaken to determine whether the innervation of the joint at 140 d gestation (17 d before birth) differed from that in the mature adult. Immunofluorescence microscopy was applied to serial sections of the capsule, disc and synovial membrane of 10 joints from 5 fetuses and image analysis was used for the quantitative assessment. The capsule, synovial membrane and the disc contained fibres immunoreactive (IR) to antisera for PGP 9.5, SP and CGRP. NPY-IR fibres were only visible in the loose connective tissue of the capsule. No VIP- or TH-IR nerve fibres were detected in the fetal TMJ. There was no statistically detectable difference between the density of nerve fibres immunoreactive to CGRP or PGP 9.5 antisera in the capsule or disc. Substance P-immunoreactivity (IR) was relatively weak in all samples examined. Scattered branches of CGRP-IR fibres were found deep in the disc proper. The lack of receptor endings, other than free nerve endings in the TMJ of the late fetal sheep, might be a reflection of the functional and anatomical immaturity of the TMJ, as reflected in the immature, gross and microscopic appearance of the disc, the inferior joint compartment and articular surface of the condyle at this stage. These results demonstrate that the capsule, synovial membrane and disc in the TMJ of fetal sheep at 140 d gestation age are innervated with sensory fibres, while autonomic fibres are located in the capsule only. The findings also support the view that the disc is innervated at an early stage of life but at a later stage the density of innervation in the central part of the disc regresses and the innervation remains only peripherally in the adult TMJ disc. Further work is required to determine (1) at what stage sympathetic fibres innervate the disc and the synovium, and (2) when the mechanoreceptive nerve endings develop.

A scientific basis for the biologic regeneration of synovial joints

Temporomandibular joint disorders represent a large group of conditions involving a local or more generalized musculoskeletal disease process. The disorders have many features and many causes and may result in limited or more severe damage of the joint associated tissues including the disks, the articular surface, the underlying bone, and the ligamentous structures. As our understanding of the molecular processes guiding skeletal tissue formation progresses, new opportunities arise in the field of skeletal tissue and joint repair. Reconstruction of the temporomandibular joint by means of scientifically designed approaches will revolutionize surgical treatment modalities.

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.

The morphogenesis of the human discomalleolar and sphenomandibular ligaments

The morphogenesis of the discomalleolar ligament and its relationship with the sphenomandibular ligament were studied in human embryos and fetuses, on histological grounds. Total number of 18 embryos and fetuses, ranging from 6.5 to 230 mm (5-25 weeks of fertilization age) were examined. The discomalleolar ligament emerged from the posterior part of the temporomandibular joint capsule and disc, passing through the squamotympanic fissure, joined the malleus. The superior fibres of the ligament inserted on the anterior process of the malleus and on the bony wall of the squamotympanic fissure. The inferior fibres of the discomalleolar ligament encircles the anterior malleolar ligament, the remnant of Meckel's cartilage, and chorda tympani, and inserted on the tympanic wall of the temporal bone. Within the tympanic cavity, the discomalleolar ligament and the anterior malleolar ligament, a continuation of the sphenomandibular ligament, formed a horizontal 'V' shape at the attachment site on the ventral surface of the malleus. The study shows that the discomalleolar ligament is an embryological continuation of the sheath of the lateral pterygoid muscle. The sphenomandibular ligament derives from Meckel's cartilage.

Temporomandibular joint development in the marmoset--a mirror of man

The timing of temporomandibular joint (TMJ) development in the cotton-eared marmoset was studied by histological examination of joints taken during embryogenesis and compared with TMJ development reported in man. Specimens were obtained via hysterotomy at intervals during pregnancies dated by estimation of uterine size or fetal head diameter. Elements of the marmoset TMJ were first identified at 70-85 days gestation, and TMJ morphogenesis was complete at 110-125 days. The chronological events of TMJ embryogenesis were found to run parallel to the human but were delayed by 30 days. At birth, after 150 days gestation, the marmoset TMJ resembled the human joint at the end of the second trimester, with all cell layers of the condylar cartilage in place and ossification started in temporal and condylar components. A new world primate, the cotton-eared marmoset is proposed as an animal model for craniofacial studies involving the TMJ on grounds of its close comparability to man.

The development of the human lateral pterygoid muscle and the temporomandibular joint and related structures: a three-dimensional approach

The development of the human fetal temporomandibular joint and surrounding structures was investigated in 11 specimens on the basis of histologic examination and three-dimensional reconstructions. Until the 10th week, there were no signs of the disc, joint spaces and capsule formation of the temporomandibular joint (TMJ). Apart from Meckel's cartilage, all the temporomandibular joint and related structures attained their adult shape at 14 weeks. Throughout the embryologic and fetal development, the relative positions of the branches of the mandibular nerve remained unchanged. From 11-12 weeks onwards, the lateral pterygoid muscle became a complex structure which was segmented by aponeuroses dividing the muscle into three main parts: superior, infero-medial and infero-anterior parts. The superior segment was attached to the TMJ disc superiorly and medially. The infero-medial segment was inserted onto the antero-medial aspect of the TMJ condyle and disc. The infero-anterior portion was attached to the anterior aspect of the condyle.

Prenatal development of the human osseous temporomandibular region

The purpose of the present study was to describe the sequence in which the lateral cranial base ossifies, particularly in the temporomandibular region. Charting the ossification sequence in the lateral normal cranial base is important for evaluating deviations in pre- and postnatal temporomandibular development. The material consisted of 74 normal human fetuses (crown-rump length = 25-228 mm). The period investigated covers the interval from the early start of ossification at 8 weeks gestational age to the occurrence of a complex ossification pattern at 21 weeks gestational age. Ossification of the cranial base in the sagittal plane is assessed mainly by radiography. The findings are confirmed by marking structures before X-ray, devisceration, and histology. This investigation confirms previous findings concerning regularity in cranial ossification sequences. In addition, the ossification in the temporomandibular region is divided into eight developmental stages according to the pattern of ossification. Thus, a developmental reference material has been established based on the following sequence in ossification of the cranial base (including the mandible and the zygomatic bone): mandible, maxilla, medial pterygoid process of the sphenoid bone, the horizontal part of the frontal bone, the zygomatic bone, the zygomatic arch of the temporal bone, the squamous part of the temporal bone and the occipital squama followed by ossification in the greater wing of the sphenoid bone, the tympanic ring, the occipital condyle, the minor wing of the sphenoid bone (anterior clinoid process), and the lateral part of the postsphenoid bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphology and analysis of the development of the human temporomandibular joint and masticatory muscle

The calcification levels of the mandible and the temporal bone of human fetuses, which ranged from 12 to 32 weeks of gestation, were systematically investigated with a soft X-ray analyzer linked to an image analyzer. The profile of the condylar process (head) revealed high levels of calcification, in contrast to that in the mandibular fossa of the temporal bone. The basal portion of the condylar process and the mandibular notch exhibited moderate calcification from 12 weeks of gestation. The weight and the cross-sectional areas of the muscle and the muscle fibers in masticatory muscles (masseter, temporal, medial, and lateral pterygoid muscles) are all increased gradually during development from 12 to 32 weeks of gestation. These changes in calcification and in cross-sectional area of muscle suggest that muscle development may be related to bone calcification during formation of the mandible.

The prenatal morphology of the articular disk of the human temporomandibular joint

The prenatal morphology and ultrastructural of the articular disk of the human temporomandibular joint was studied to determine their relationship to the corresponding adult characteristics. The articular disks of seven human fetuses ranging in age from 10 to 32 weeks' gestation were examined. Our results show that the fetal articular disk has a genetically pre-determined appearance that substantially prefigures that of the adult. In profile, it was seen to be thin at the center and thick toward the periphery, like the adult structure; likewise, it was denser centrally than peripherally. Basically, it was found to be a fibrous structure: it was composed of a large number of connective tissue cells, while the blood vessels were limited to the periphery. A large number of elastic fibers was also observed. Posteriorly, they had a longitudinal orientation along the junction with the postglenoid tubercle of the temporal bone; along the periphery, they ran in an annular fashion.

[Ontogeny of the human temporomandibular joint]

An analysis of the human temporomandibular joint is done regarding to the appearance of secondary cartilage formations during the prenatal development of condylus and temporal joint elements. Sagittal sections of nine human fetuses (49 mm CRL to 315 mm CRL) show a closed relationship between the development of the bony and soft tissues of the joint. The temporary appearance of secondary cartilage in the temporal joint area is induced by the functional loading of the capitulum. This process requires the genesis of the two free articular cavities on the one side and the functional attachment of the lateral pterygoid muscle to the discus and the collum mandibulae on the other. Pointing out the clear relationship of the articulating joint surfaces and the in between discuss, a left temporomandibular joint of a fetus (125 mm CRL) is reconstructed in a medioventral view with the help of a three dimensional drawing. The location of the temporal secondary cartilage formation within the centre of the temporal loading area of the condyle assures its functional genesis during the embryological development of the human temporomandibular joint.

[The temporomandibular joint (TMJ) and osteogenesis imperfecta. A study of its embryologic development]

Although the most common oral manifestation of osteogenesis imperfecta is dentinogenesis imperfecta, several authors have described jaw fractures and radiolucent bone lesions associated with this disease. The authors, after reporting the main features of this disease, compare the cranial embryologic growth in twice fetuses of a 15 weeks old: one of these with osteogenesis imperfecta.

The embryologic development of the human lateral pterygoid muscle and its relationships with the temporomandibular joint disc and Meckel's cartilage

The morphology of the developing lateral pterygoid muscle and its relationships with the temporomandibular joint disc and Meckel's cartilage were studied in 16 human embryos and fetuses ranging in age from 5 weeks to 14 weeks. All the temporomandibular joint structures and the lateral pterygoid muscle assumed their adult shapes by the 14th week of fetal life. At this stage, the lateral pterygoid muscle is a complex structure with several aponeuroses dividing the muscle into three main parts: superior, inferomedial, and inferoanterior. The superior part is attached to the disc superiorly and medially. The inferomedial part inserts into the anteromedial aspect of the condyle and disc. The inferoanterior portion is attached to the anterior aspect of the condyle. Anteriorly, the buccal nerve and associating blood vessels traverse the muscle in a mediolateral direction, dividing it into superior (small) and inferior (large) compartments. Posteriorly, the muscle remains intact with no separation. The lateral pterygoid muscle fibers show no direct attachment to Meckel's cartilage at any stage of development.

Development and histology of fibrous architecture of the fetal temporomandibular joint

The developmental history of the temporomandibular joint (TMJ) was investigated in 10 fetuses of 4 to 10 months of gestational age. The S-type structure of the disc is formed by the following bases: 1) the flat upper and concave lower surfaces of the disc; 2) thinner intermediate zone and thicker anterior and posterior bands; 3) the projection of the articular tuberculum and superoposterior growth of the condyle. The posterolateral part of the disc was the thickest and the corresponding part of the fossa was the deepest. The condyle was originally positioned beneath the part of disc that was considered the main force-bearing area. The distribution and arrangement of elastic and collagen fibers in the disc was proportional to disc function. Gross elastic fibers in the posterolateral part of the posterior band were connected with the upper head of the pterygoideus lateralis muscle fibers running medioanteriorly. They were indicated to be antagonistic with each other. At 4 months of gestational age, a few elastic fibers appeared in the bilaminar region and began to form bundles as the fetus grew. At full-term dense elastic fibers were found in the upper stratum of the bilaminar region.

The relationships between the temporomandibular joint disc and related masticatory muscles in humans

A study of the relationships of the temporomandibular joint disc and the lateral pterygoid, temporalis, and masseter muscles during the human fetal period and in the adult was conducted. The superior head of the lateral pterygoid muscle was seen to insert into the anteromedial two thirds of the temporomandibular joint disc. The fibers of the posterior one third of the temporalis muscle and fibers of the deep bundle of the masseter muscle were attached on the anterolateral one third of the disc. The attachment of these muscles to the disc was through the anterior extension of the disc, also known as the premeniscal or prediscal lamina. The possible functional role of these muscle attachments is discussed.

The development of the temporomandibular joint: a review with regard to the lateral pterygoid muscle

This review sets out to explore the relationship between the lateral pterygoid muscle and the meniscus. It examines the embryological evidence to explain the controversy surrounding the apparent morphological discrepancy in the attachment of the lateral pterygoid muscle to the meniscus. It shows that the contribution of the lateral pterygoid muscle to the formation of the meniscus remains in dispute. Morphogenetic studies have not been able to support either one or other viewpoint and no direct conclusions can therefore be made on the embryology of the temporomandibular joint.

Developmental anatomy of the mouse stapediovestibular and temporomandibular joints

The genesis, development and growth of the mouse stapediovestibular joint (SVJ), which contains the annular ligament, and the temporomandibular joint (TMJ) were examined in an attempt to study the stress-bearing articular tissue that is thought to be derived from embryonic mesenchyme; the findings were also compared with those in the ossicular joints. The following conclusions were obtained: 1) The articular cartilage of the mandibular condylar process, stapedial foot plate and otic capsule is derived from fetal fibrous articular tissue. 2) The fetal TMJ developed into a typical double diarthroses containing an articular disc. 3) The fetal syndesmodial SVJ differentiated into the annular ligament containing characteristic palisade-like fibroblasts and hammock-like fibers; no interzone formation or synovial cavities were observed in the completed and mature syndesmodial SVJ. 4) Like the TMJ, the major elastic system fibers in the annular ligament were also mechanical-resistant elaunin. 5) Elastogenesis was closely related to functional and mechanical factors in the auditory ossicular chain, TMJ and annular ligament; the mature incudomalleal and incudostapedial joints contained mainly mature elastic fibers, but the mature SVJ and immature TMJ contained mainly pre-elastic elaunin fibers. 6) Stress elastosis, turnover of the fibrillar component and age changes in cellular and fibrous components were not evident in either the mature SVJ or the young functional TMJ.

Relationships between the temporomandibular joint and the middle ear in human fetuses

A study was conducted, on 30 human fetuses, of the structures passing through the tympanosquamosal fissure. The tympanosquamosal fissure lies between the middle ear and the temporomandibular region. Meckel's cartilage passes through the tympanosquamosal fissure and continues on into the middle ear with the cartilaginous anlage of the malleus. A tract of fibrous tissue arises from the mesenchyme, located cranial and lateral to Meckel's cartilage, that enters from the posterior area of the temporomandibular joint disc to the middle ear through the tympanosquamosal fissure, and attaches onto the area of continuity of Meckel's cartilage with the malleus. Transformation of Meckel's cartilage into the sphenomandibular ligament and anterior ligament of the malleus determines their continuity through the tympanosquamosal fissure. The posterior fibers of the temporomandibular joint disc giving rise to the discomalleolar ligament insert into the anterior ligament of the malleus.

Development of collagen fibers and vasculature of the fetal TMJ

Using 12 human fetuses, histological development and changes in connective fiber structure and fine vascular patterns have been investigated in various fetal gestational stages by light and scanning electron microscopy. The main arterial supply of the articular disc was from the bilaminar region and pterygoideus lateralis muscle. The vascular network on the disc surface was related with fluid secretion. When the bilaminar region was compressed, it caused ischemia and fibrosis as the main pathological changes in TMJ derangement. A decrease in fluid from blood vessels might occur in TMJ degeneration. Collagen fibers in the disc passed mainly anteroposteriorly. In the anterior and posterior bands, muscular tendon fibers came from the pterygoideus lateralis muscle and superior stratum of the bilaminar region. In the posterior band three-dimensional structures of collagen fibers suitable for load bearing were observed. The compass network and process on the disc showed the normal structure that is formed gradually and has functions including dispersion, pressure bearing, friction-proofing and storage of the synovial fluid. Attachments of the disc were suitable for disc function. Large elastic fibers in the posterolateral part of the superior stratum of the bilaminar region may be antagonistic to the upper head of the pterygoideus lateralis muscle fibers passing medioanteriorly, indicating that this antagonism is available for disc function.

Development of the rabbit craniomandibular joint in association with tooth eruption

The adult rabbit craniomandibular joints (CMJs) are stress-bearing joints. The two CMJs and the teeth form an articular triad. In early fetal life the developing triad consists of the CMJ primordia, the tooth germs for the entire set of deciduous teeth, as well as the posterior extensions of the dental lamina, which will give rise to the permanent teeth with no deciduous predecessors. During postnatal life, before occlusion is established, there is a remodelling stage in which the CMJ builds up its matrix components such as collagenous and elastic fibres, proteoglycans and type II collagen. Remodelling gradually diminishes into the maintenance stage once occlusion is fully established and after eruption of the first and second molars. Chondrocytes first appear in the CMJ articular disc during the second week of postnatal development. These cells localize in the band areas of the disc and establish an extensive cartilaginous matrix 3-4 weeks postnatally. This study supports the concept that the full development of a fibrocartilaginous articular disc, rich in proteoglycans, occurs as adult occlusion is established.

[A histological study of the meniscal insertion of the external pterygoid muscle]

The paper reports a study of the relationship between the upper head of the pterygoid muscle and the temporomandibular joint disc. Using optical microscopy, TMJ serial sections of 10 human embryos and fetuses aged from 6 to 22 weeks were examined. From the observation of serial sections, it appears that from the start of histogenesis the lateral pterygoid muscle is in contact with the condylar blastema and later with the disc and the condyle. A fibrous attachment was detected between the muscle tendon and the meniscus, and oxytalan and elastic fibres were observed near this attachment.

[Structure and ultrastructure of the human TMJ meniscus]

This ultrastructural study is concerned on demonstrating the presence and the distribution of the elastic system fibers in human TMJ disc. Oxytalan and pre-elastic fibers were found to occur in the anterior, intermediate and posterior band of the disc. These fibers run parallel to collagen fibers in the outer portion of the disc while in the deeper portion they were canted compared to collagen fibers arrangement. The presence of an elastic system fibers in human TMJ disc it is plausible to assume that it enables the disc to resist to a wider range of reversible deformation.

The anterior ligament of the human malleus

The authors have studied the anterior ligament of the malleus (ALM) from a morphological and embryological point of view. Classical textbooks of anatomy stress the correlation between the ALM and the anterior pin of the sphenoid and define the ligament as a residual of Meckel's cartilage. This study demonstrates the y-shaped form of the ligament, one arm of which reaches the capsule of the temporomandibular joint and the other the pin of the sphenoid bone. Meckel's cartilage pilots the fibres of the ligament itself. Several clinical implications may be hypothesised on the basis of this study.