The uptake of horseradish peroxidase in monkey temporomandibular joint synovium after occlusal alteration

Ultrastructural study of synovitis induced by trauma to the rat temporomandibular joint (TMJ)

BACKGROUND

Electron microscopy was used to examine the histologic effect of trauma on the rat temporomandibular joint synovial membrane.

METHODS

Trauma to the TMJ in male Wister rats (100-200 g) was introduced through repeated forced condylar hypermobility. Ultrastructural observations were made 5 days and 6 weeks after the trauma.

RESULTS

The early response of the synovial membrane was synovial hyperplasia, type A synovial cell loss, dilation of the r-ER in the type B synovial cells and fibrin deposition on the synovial surfaces. The late response included degeneration of synovial cells with swollen mitochondria and cell projections, and cell fragmentation. Large amount of fibrin deposition on opposing surface layers was also noticed.

CONCLUSION

The type A cell loss and fibrin deposition followed by the occurrence of fibrinous materials at opposing surface layers of the synovial membrane suggest that traumatic synovitis causes synovial adhesions.

Prevalence of missing posterior teeth and intraarticular temporomandibular disorders

STATEMENT OF PROBLEM

The association between missing mandibular posterior teeth and the development of intraarticular temporomandibular disorders (TMDs) remains unclear.

PURPOSE

The purpose of this study was to evaluate the prevalence of missing mandibular posterior teeth and intraarticular TMDs in a mixed population of asymptomatic subjects and symptomatic TMD patients.

MATERIAL AND METHODS

Eighty-two asymptomatic volunteers and 263 symptomatic TMD patients were included in this study. Asymptomatic volunteers completed a subjective questionnaire and underwent clinical examination to document the absence of TMD signs and symptoms. All symptomatic subjects had localized jaw joint pain and pain on movement or when eating. The number of missing mandibular bicuspid and molar teeth (excluding third molars) in each subject was recorded, and magnetic resonance images were made to document the presence or absence of disk displacement in the temporomandibular joints. Subjects were divided into 4 groups: group 1 = asymptomatic, normal magnetic resonance imaging result; group 2 = asymptomatic, disk displacement; group 3 = symptomatic, normal magnetic resonance imaging result; and group 4 = symptomatic, disk displacement. Collected data were analyzed with chi-square tests (P<.05) with no adjustment for multiple comparisons.

RESULTS

A positive association between missing mandibular posterior teeth and the presence of disk displacement was found.

CONCLUSION

The literature does not suggest that replacement of missing posterior teeth prevents the development of TMDs. However, missing mandibular posterior teeth may accelerate the development of degenerative joint disease.

Postnatal development of substance P-, calcitonin gene-related peptide- and neuropeptide Y-like immunoreactive nerve fibres in the synovial membrane of the rat temporomandibular joint

The postnatal (0-24 days) development of substance P (SP)-, calcitonin gene-related peptide (CGRP)- and neuropeptide Y(NPY)-like immunoreactive (LI) nerves in the rat temporomandibular joint (TMJ) was investigated immunohistochemically. Immediately after birth, SP- or CGRP-LI nerves were observed in most disc attachments. A few NPY-LI nerves were observed around the large blood vessels in the joint capsule. From days 3 to 6, the SP- or CGRP-LI nerves were first found close to the anterior, lateral, medial (third day) or posterior (sixth day) peripheral portion of the disc. The synovial cells (type A and B) first appeared at the anterior peripheral portion of the disc (sixth day), and then at the posterior, lateral and medial portions (seventh day). NPY-LI nerves were found around the blood vessels at the disc attachment on the sixth day, and then entered into the peripheral portion of the disc from days 10 to 14. At 14 days a few NPY-LI nerves were first found close to the blood vessels in the sublining layer of the synovial membrane. From days 18 to 24, a few NPY-LI nerves were located in the superficial layer of the synovial membrane. The central portion of the disc did not contain any nerves from days 0 to 24. Thus SP- or CGRP-LI sensory nerves are shown to innervate the rat TMJ at an earlier age than NPY-LI sympathetic nerves, which may modulate the regulation of blood flow in the joint capsule, disc and synovial membrane. However, it is considered that the disc itself does not contribute to the transportation of the afferent sensory information. Furthermore, from the fact that SP- or CGRP-LI nerves were found earlier than the appearance of the synovial cells, it is suggested that these nerves may be associated with the growth and proliferation of synovial cells.

Postnatal development of protein gene product 9.5- and calcitonin gene-related peptide-like immunoreactive nerve fibers in the rat temporomandibular joint

BACKGROUND

The aim of this study was to investigate the little-known postnatal development of innervation in the temporomandibular joint (TMJ).

METHODS

We therefore investigated the protein gene product 9.5-like immunoreactive (PGP-LI) and calcitonin gene-related peptide-like immunoreactive (CGRP-LI) nerves in the rat TMJ from days 0-24 in wholemount preparations and frozen sections by immunohistochemistry using the avidin-biotin-peroxidase complex method.

RESULTS

At birth, PGP-LI and CGRP-LI nerves were observed only in the disk attachment but not in the peripheral portion of the disk. From days 3-6, the peptidergic nerves associated with the development of synovial cells were first found in the anterior (3rd day) or posterior (6th day) peripheral portion of the disk in which synovial cells later appear. From days 7-10, incisal occlusion started and simultaneously the distinct networks of the nerves were formed in four peripheral portions of the disk. On the 14th day, the PGP-LI nerves were first more numerous than the CGRP-LI nerves only in the anterior disk attachment. From days 18-24, the occlusion between the first molars started. Simultaneously, the distribution and number of the nerves were comparable to those of adult rats. However, from days 0-24, the central portion of the disk (actual disk) did not contain any nerves.

CONCLUSIONS

These findings suggest that functional stimuli such as sucking and mastication might be associated with the development of nerves in the TMJ during the early and late postnatal days, whereas the actual disk except for both disk attachment and peripheral portion of the disk is not innervated and does not contribute to the afferent sensory information from the TMJ. The presence of peptidergic nerves prior to the appearance of synovial lining cells furthermore suggests that the neuropeptide released from these nerves may affect on the differenciation and maturation of synovial cells.

A topographical and ultrastructural study of sensory trigeminal nerve endings in the rat temporomandibular joint as demonstrated by anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP)

To extend our previous light microscopic observations concerning the distribution of trigeminal sensory nerves in the synovium of the rat temporomandibular joint, we investigated the detailed distribution and fine structure of sensory nerve endings at the light and electron microscopic level by the anterograde transport method using wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injected into the trigeminal ganglion. At the light microscopic level, HRP-labeled nerve fibers were observed in the joint capsule and peripheral portion of the disc. The anterior portion of the disc was more densely innervated than the posterior portion, while no nerves were found in the central portion. At the electron microscopic level, HRP reaction products were observed intra-axonally in the thinly myelinated (A delta) and unmyelinated (C) axons in the anterior portion of the joint capsule, and were also localized in the extracellular space surrounding the unmyelinated fibers and terminals. In the subsynovial layer of the synovial membrane, the majority of labeled axons located near blood vessels or among the collagenous fibrils were covered by Schwann cell sheaths, although some naked axon terminals without sheaths were also found. These unsheathed terminals contained mitochondria, small clear vesicles, and large granular vesicles, and were close to the synovial A and/or B cells near the joint cavity. The minimum distance between the terminals and synovial cells was 75 nm. This is the first demonstration of trigeminal sensory nerve terminals close to synovial lining cells or joint cavity and suggests that neuropeptides such as substance P may be released close to the synovial lining cells or joint cavity.

Immunocytochemical localization of cathepsin L in the synovial lining cells of the rat temporomandibular joint

Localization of cathepsin L in the synovial lining cells of the normal rat temporomandibular joint was investigated by the avidin-biotin-peroxidase complex method for semithin (1 microns) cryosections and the colloidal gold-labelled IgG method for ultrathin sections of LR gold resin. At the light-microscopic level, type A (macrophage-like) and B (fibroblast-like) cells formed the synovial lining layer. Extensive immunoreactivity for cathepsin L was observed in many granules and vacuoles of type A cells, while in the type B cells, immunoreactivity was found in very few granules. In the sublining layer, macrophages and a few fibroblasts were positive for cathepsin L. By electron microscopy, at the peripheral cytoplasm of the type A cells close to the lateral intercellular spaces and joint cavity, numerous coated vesicles and vacuoles (probably early endosomes) indicating endocytotic function were found. Gold particles indicating cathepsin L were localized in the vesicles (primary lysosomes) in the perinuclear cytoplasm and in the larger amorphous vacuoles (1 microns dia) as phagolysosomes. In type B cells, gold particles were limited to the vesicles only (primary lysosomes). The cathepsin L-positive primary lysosomes were numerous in a few fibroblasts in the sublining layer. These results indicate that type A cells contain a large amount of cathepsin L, and suggest that these cells endocytose surplus substances such as collagen and proteoglycan fragments in normal rat TMJ, effecting their digestion and degradation by the action of this proteolytic cathepsin.

Histopathological and immunocytochemical studies of the effect of raised occlusal vertical dimension on the condylar cartilage of the rabbit

The objective of this study was to evaluate the effect of raising the vertical dimension of occlusion on the condylar cartilage of young adult rabbits. Ten rabbits of approximately the same age were divided into two equal control and experimental groups. The vertical dimension of occlusion of the experimental group was raised bilaterally 1.5 mm using composite resin. No procedure was done for the control group. Animals were sacrificed during a six week period, and changes in condylar cartilage of experimental animals (compared to controls) were evaluated histomorphometrically. In addition, alterations of collagen type I and II were detected using immunohistochemical techniques. The results demonstrated an increase in the volume of the experimental condylar cartilage, which was attributed to an increase in the cartilage zone. Immunohistochemical examination of the hyperplastic cartilage showed no evidence for the production of type I collagen. These changes in condylar cartilage were considered adaptive and may lead to change in condylar shape. Further studies are needed to show if these adaptive changes would progress into osteoarthritis.

Immunohistochemical localization of cathepsins B and D in the synovial lining cells of the normal rat temporomandibular joint

In 1 micron-thick serial cryosections, cathepsins B and D were found to coexist in both type A (macrophage-like) and type B (fibroblast-like) cells: the whole cytoplasm of the type A cells showed strong immunoreactivity, while the type B cells contained a few granular reaction products. It is therefore suggested that type A cells have a marked ability for intracellular digestion of organic materials.

Distribution of substance P and calcitonin gene-related peptide-like immunoreactive nerve fibers in the rat temporomandibular joint

The density and distribution of substance P-like immunoreactive (SP-LI) and calcitonin gene-related peptide-like immunoreactive (CGRP-LI) nerve fibers in rat temporomandibular joint (TMJ) were investigated in whole-mount preparations and frozen sections by immunohistochemistry with the avidin-biotin-peroxidase complex method. Both types of immunoreactive nerves were observed primarily in the joint capsule, the peripheral articular disc, the synovial membrane, and the periosteum. The distribution of CGRP-LI nerves was similar to that of SP-LI nerves. The anterior portion of the joint capsule and disc was most densely innervated, followed by the posterior, lateral, and medial portions. In addition, CGRP-LI nerves were more numerous and more dense in immuno-intensity than SP-LI nerves. In the synovial membrane, many SP- and CGRP-LI nerves terminated in the subsynovial layer, but some branches extended into the superficial synovial lining layer close to the joint cavity. Immunolabeled nerves were prominently located in the disc attachment and peripheral portion of the disc, and occasional nerves were located in the dense collagenous disc band as an actual disc. However, no fibers were detected in the central disc band. Thus, most of the disc was not innervated by any nerves. The present study provides a morphological basis for the possible roles of neuropeptides in endocytosis by synoviocytes, regulation of blood flow in the synovial membrane, nociception mechanisms of the TMJ, and modulation of the inflammatory response in the TMJ.

Relationship of occlusal vertical dimension to the health of the masticatory system

Changes in occlusal vertical dimension have been claimed to cause masticatory system disorders. Early articles on this subject were mainly limited to clinical case reports, and the more recent clinical studies have been flawed by the lack of control groups, blind evaluation, and by poor definition of criteria for evaluating the health of the masticatory system. Research with humans and animals has shown that if increases in occlusal vertical dimension are not extreme and the appliance used covers most of the dentition, there is a good possibility of adaptation. Current scientific knowledge does not support the hypothesis that moderate changes in occlusal vertical dimension are detrimental to the masticatory system.

The peripheral distribution of trigeminal nerve fibres in the rat temporomandibular joint studied by an anterograde axonal transport method with wheat germ agglutinin-horseradish peroxidase

Wheat germ agglutinin-horseradish peroxidase was injected into the trigeminal ganglion to trace the peripheral distribution of the nerve fibres in the temporomandibular joint. It was transported anterogradely along trigeminal nerve fibres. Horseradish-peroxidase-labelled nerve fibres were found in the anterior and posterior bands of the articular disc, and terminated as nerve endings near the intermediate zone of the disc. However, the intermediate zone itself did not contain any nerve endings. Other nerve fibres penetrated from the subsynovial layer into the synovial membrane and also terminated as nerve endings close to the articular cavity. Thus, this method is suitable for tracing peripheral nerve fibres and nerve endings originating in the trigeminal ganglion.

Histopathological study of human TMJ perforated discs with emphasis on synovial membrane response

Fifteen perforated TMJ discs from human cadavers were studied histologically to examine the synovial membranes and to compare the findings with previous experimental results in monkeys. There were four with perforations in the bilaminar zone (these four discs were displaced anteriorly), three in the medial third of the disc, and eight in the lateral third of the disc. Histopathologically, there was an increase in vascularity and strong methyl pyronine-positive cellularity around the margins of the perforations. A young, loose, collagenous tissue lined the lateral margins of the perforated discs. Increased fibrous tissue content of the synovial subintimal territorial matrix and osteochondroid metaplasia were also seen. Severe synovial hyperplasia was visible in all joint recesses, but was greatest within those associated with displaced discs. There was patchy distribution of acidic glycoproteins, especially in the lateral parts of the perforated discs. As in the animal studies, human TMJ disc perforation was associated with a vigorous synovial reaction that was seen to form lateral bridges along the margins.