An experimental model of osteoarthrosis in the temporomandibular joint of the rabbit

Short term histopathological effects of GaAlAs laser on experimentally induced TMJ osteoarthritis in rabbits

The aim of this study was to evaluate the biostimulation (BS) effect of the gallium-aluminum-arsenide (GaAlAs) diode laser by histopathology with an experimental osteoarthritis (OA) model in the temporomandibular joints (TMJ) of rabbits, in the early period. GaAlAs diode laser is used for pain reduction in TMJ disorders. Twenty-four adult male New Zealand white rabbits were randomly divided into three equal groups: Control Group (CG), Study Group 1 (SG-1), and Study Group 2 (SG-2). Mono-iodoacetate (MIA) was administered to the right TMJs of all rabbits. The rabbits did not undergo any treatment for four weeks to allow the development of osteoarthritis. In SG-1, laser BS was applied to the rabbits at 940 nm, 5 W, and 15 J/cm2 in continuous wave mode at 48-hour intervals for 14 sessions; and in SG-2, laser BS was applied with the same parameters at 24-hour intervals for 28 sessions. Laser BS was not applied to the rabbits in CG. All rabbits were sacrificed simultaneously. The TMJ cartilage, osteochondral junction, chondrocyte appearance, and subchondral ossification were evaluated histopathologically. There was no statistically significant difference between the groups in terms of cartilage, osteochondral junction, chondrocyte appearance, and subchondral ossification values (p > 0.05). The laser BS protocol used in the study had no positive histopathological effects on TMJ OA in the early period.

Preclinical Animal Models for Temporomandibular Joint Tissue Engineering

There is a paucity of in vivo studies that investigate the safety and efficacy of temporomandibular joint (TMJ) tissue regeneration approaches, in part due to the lack of established animal models. Review of disease models for study of TMJ is presented herein with an attempt to identify relevant preclinical animal models for TMJ tissue engineering, with emphasis on the disc and condyle. Although degenerative joint disease models have been mainly performed on mice, rats, and rabbits, preclinical regeneration approaches must employ larger animal species. There remains controversy regarding the preferred choice of larger animal models between the farm pig, minipig, goat, sheep, and dog. The advantages of the pig and minipig include their well characterized anatomy, physiology, and tissue properties. The advantages of the sheep and goat are their easier surgical access, low cost per animal, and its high tissue availability. The advantage of the dog is that the joint space is confined, so migration of interpositional devices should be less likely. However, each species has limitations as well. For example, the farm pig has continuous growth until about 18 months of age, and difficult surgical access due to the zygomatic arch covering the lateral aspect of joint. The minipig is not widely available and somewhat costly. The sheep and the goat are herbivores, and their TMJs mainly function in translation. The dog is a carnivore, and the TMJ is a hinge joint that can only rotate. Although no species provides the gold standard for all preclinical TMJ tissue engineering approaches, the goat and sheep have emerged as the leading options, with the minipig as the choice when cost is less of a limitation; and with the dog and farm pig serving as acceptable alternatives. Finally, naturally occurring TMJ disorders in domestic species may be harnessed on a preclinical trial basis as a clinically relevant platform for translation.

COMPUTED TOMOGRAPHIC APPEARANCE OF THE TEMPOROMANDIBULAR JOINT IN 1018 ASYMPTOMATIC HORSES: A MULTI-INSTITUTION STUDY

Published descriptions of nonseptic arthritis of the equine temporomandibular joint (TMJ) are rare and large studies investigating variations in the TMJ for asymptomatic horses are lacking. The objectives of this cross-sectional, retrospective, multi-institutional study were to describe anatomical variations in the TMJ detected using computed tomography (CT) in an equid population asymptomatic for TMJ disease and determine whether these variations were associated with patient signalment, reason for CT examination, or CT slice width. Medical records at eight hospitals were searched for horses that had head/neck CT scans and no clinical signs of TMJ disease. Age, breed, sex, clinical presentation, and CT slice width data were recorded. Alterations in CT contour and density of the mandibular condyles, mandibular fossae, and TMJ intra-articular discs were described for each horse. Generalized logistic regression was used to test associations between anatomical variations and horse age. A total of 1018 horses were sampled. Anatomical variations were found in TMJ CT images for 40% of horses and 29% of joints. These were dichotomous with regard to age. Horses <1 year old commonly had alterations in the shape and density of the mandibular condyle. Older horses commonly had spherical hypodensities within the mandibular condyles consistent with bone cysts; and hyperdense regions of the intra-articular disc consistent with dystrophic mineralization. Findings indicated that TMJ anatomic variations were common in CT images of younger and older horses asymptomatic for TMJ disease. Future studies are needed to more definitively characterize these CT variations using gross pathology and histopathology.

Temporomandibular joint fibrocartilage degeneration from unilateral dental splints

OBJECTIVE

The objective of this study was to determine the extent to which altered loading in the temporomandibular joint (TMJ), as might be associated with a malocclusion, drives degeneration of articulating surfaces in the TMJ. We therefore sought to quantify the effects of altered joint loading on the mechanical properties and biochemical content and distribution of TMJ fibrocartilage in the rabbit.

DESIGN

Altered TMJ loading was induced with a 1mm splint placed unilaterally over the maxillary and mandibular molars for 6 weeks. At that time, TMJ fibrocartilage was assessed by compression testing, biochemical content (collagen, glycosaminoglycan (GAG), DNA) and distribution (histology), for both the TMJ disc and the condylar fibrocartilage.

RESULTS

There were no changes in the TMJ disc for any of the parameters tested. The condylar fibrocartilage from the splinted animals was significantly stiffer and the DNA content was significantly lower than that in control animals. There was significant remodeling in the condylar fibrocartilage layers as manifested by a change in GAG and collagen II distribution and a loss of defined cell layers.

CONCLUSIONS

A connection between the compressive properties of TMJ condylar fibrocartilage after 6 weeks of splinting and the changes in histology was observed. These results suggest a change in joint loading leads to condylar damage, which may contribute to pain associated with at least some forms of TMJ disease.

Functional analysis of the rabbit temporomandibular joint using dynamic biplane imaging

The dynamic function of the rabbit temporomandibular joint (TMJ) was analyzed through non-invasive, three-dimensional skeletal kinematics, providing essential knowledge for understanding normal joint motion. The objective of this study was to evaluate and determine repeatable measurements of rabbit TMJ kinematics. Maximal distances, as well as paths were traced and analyzed for the incisors and for the condyle-fossa relationship. From one rabbit to another, the rotations and translations of both the incisors and the condyle relative to the fossa contained multiple clear, repeatable patterns. The slope of the superior/inferior incisor distance with respect to the rotation about the transverse axis was repeatable to 0.14 mm/deg and the right/left incisor distance with respect to the rotation about the vertical axis was repeatable to 0.03 mm/deg. The slope of the superior/inferior condylar translation with respect to the rotational movement about the transverse axis showed a consistent relationship to within 0.05 mm/deg. The maximal translations of the incisors and condyles were also consistent within and between rabbits. With an understanding of the normal mechanics of the TMJ, kinematics can be used to compare and understand TMJ injury and degeneration models.

Autologous adipose stem cells and polylactide discs in the replacement of the rabbit temporomandibular joint disc

The temporomandibular joint (TMJ) disc lacks functional replacement after discectomy. We investigated tissue-engineered bilayer polylactide (PLA) discs and autologous adipose stem cells (ASCs) as a potential replacement for the TMJ disc. These ASC discs were pre-cultured either in control or in differentiation medium, including transforming growth factor (TGF)-β1 for one week. Prior to implantation, expression of fibrocartilaginous genes was measured by qRT-PCR. The control and differentiated ASC discs were implanted, respectively, in the right and left TMJs of rabbits for six (n = 5) and 12 months (n = 5). Thereafter, the excised TMJ areas were examined with cone beam computed tomography (CBCT) and histology. No signs of infection, inflammation or foreign body reactions were detected at histology, whereas chronic arthrosis and considerable condylar hypertrophy were observed in all operated joints at CBCT. The left condyle treated with the differentiated ASC discs appeared consistently smoother and more sclerotic than the right condyle. The ASC disc replacement resulted in dislocation and morphological changes in the rabbit TMJ. The ASC discs pre-treated with TGF-β1 enhanced the condylar integrity. While adverse tissue reactions were not shown, the authors suggest that with improved attachment and design, the PLA disc and biomaterial itself would hold potential for TMJ disc replacement.

Sodium iodoacetate induced osteoarthrosis model in rabbit temporomandibular joint: CT and histological study (part I)

Studies to elucidate the pathophysiology of osteoarthrosis have been hampered by the lack of a rapid, reproducible animal model that mimics the histopathology and symptoms associated with the disease. The aim of this study is to evaluate the radiological, histological and histomorphometrical findings of four different concentrations of sodium iodoacetate (MIA) to create osteoarthrosis by using an arthrocentesis technique on rabbit temporomandibular joint (TMJ). 12 New Zealand white male rabbits received an injection of MIA (50 μl dose of 1.5, 2, 2.5, 3mg/ml concentrations) to a single joint of each group by arthrocentesis. Computed tomography (CT) images were obtained pre- and post-injections at 2, 4 and 6 weeks. Early osteoarthritic changes in the rabbit TMJ were found histologically at 4 weeks and with a 3mg/ml concentration of MIA. The mean subchondral bone volume depended on the concentration of MIA and was 62±2.6%, 63±4.1%, 42±3.6% and 38±3.8%, respectively. A minor abnormality was found on CT in six joints at the 4-week follow up. MIA injection and arthrocentesis offer a rapid and minimally invasive method of reproducing histologically osteoarthrotic lesions in the rabbit TMJ.

Chondrogenic effect of the perichondrium graft on the internal derangement and osteoarthritis of the temporomandibular joint of the rabbit

Internal derangement of the temporomandibular joint is usually defined as the disruption of the condyle and disc relationship. In addition to this description the other elements of the joint including the cartilage surface, synovial fluid, the ligaments and the bony surface itself demonstrate varying degrees of pathology in concordance with the stage of the internal derangement, as well. This study is designed to create an osteoarthritic model in the rabbit temporomandibular joint. A 2×2mm defect was performed on the cartilage surface of the both condyles of each animal (n=30). The osteoarthritic changes were demonstrated by computerised tomography sections. The right joints of the animals constituted the control group and the left, the study group. At the time of the defect generation, a perichondrium graft from the animal's ear was implanted onto the defect in the study group. The control group was left to heal secondarily. The joints of three randomized groups of 10 animals for each were inspected at the 4th, 6th, and 8th weeks. Cartilage regeneration and regression of the osteoarthritic changes were demonstrated in the study group both in the 6th and 8th week groups. However, the control group showed less cartilage regeneration and progression of the osteoarthritic changes in all weeks, with progression with time. The perichondrium graft has demonstrated chondrogenic effect on the condyle and this in turn changed the progression to internal derangement.

Validation of a chemical osteoarthritis model in rabbit temporomandibular joint: a compliment to biomechanical models

To explore degenerative mechanisms occurring in the temporomandibular joint (TMJ), a chemical model of knee joint osteoarthritis using sodium mono-iodoacetate injection was transposed to the TMJ. Twelve New Zealand rabbits were used to document the effect of this drug on the TMJ. Eight rabbits underwent bilateral iodoacetate injection in the disco-condylar compartment while 4 served as controls. Rabbits were sacrificed at 10, 20, 30 and 40 days and joints studied by histology. Severity of the damage was time dependent and the use of iodoacetate allowed the observation, within a few weeks, of every osteoarthritic stage usually described in the literature. This study showed that the TMJ has a specific response to the degenerative process. This response was characterized by (i) thickening and fibrillation of the cartilage at the periphery of the lesion, tending to reduce mechanical stress in the lesional area and (ii) chondrocyte migration under areas where subchondral bone surface was locally destroyed. The extracellular matrix containing chondrocyte clusters and prechondrocytes dived around the bony defect and proceeded below the necrotic bone to promote the eviction of bony fragments into the joint cavity, pushing them up while the thickness of chondrocyte rows increased below. This could be interpreted as a repairing attempt due to the specific potential of fibrocartilage proliferative cells.

Microscopic changes in the condyle and disc in response to distraction osteogenesis of the minipig mandible

PURPOSE

Unilateral mandibular distraction osteogenesis (DO) has been shown to cause gross changes in the mandibular condyle and articular disc. The purpose of this study was to correlate histologic findings with these gross changes in a minipig distraction model.

MATERIALS AND METHODS

Semiburied distractors were placed via submandibular incisions in 15 minipigs. Two unoperated animals served as controls. The protocol consisted of 0-day latency and rates of 1, 2, or 4 mm/day for a 12-mm gap. After the minipigs were killed (at 0, 24, or 90 days), ipsilateral and contralateral condyles and discs were harvested, decalcified, prepared for standard paraffin embedding, and evaluated to determine changes in 1) morphology and thickness of the articular cartilage and subchondral bone and 2) morphology of the disc.

RESULTS

In control animals, there were no degenerative changes in the articular cartilage and underlying condylar bone; there were no significant differences in the mean articular cartilage thickness. The temporomandibular joint discs were normal. In experimental animals, distracted condyles showed increasing degenerative changes and mean articular cartilage thickness as the DO rate increased. The discs were thinner. These changes were present, but to a lesser degree, in the contralateral condyles. After 90 days, degenerative changes in the condyles and discs were reduced, after remodeling, except in the 4 mm/day DO group.

CONCLUSIONS

Histologic changes in the condyles and temporomandibular joint discs in response to mandibular DO correlated with previously reported gross changes. These changes were greater at higher distraction rates and remodeling back to normal occurred in mandibular condyles distracted at 1 mm/day.

Expression of proteoglycan mRNA in patients with painful clicking and chronic closed lock of the temporomandibular joint

RT-PCR was used to analyze the expression of a series of mRNAs coding for proteoglycans aggrecan, versican, biglycan, decorin, fibromodulin and also hyaluronan synthase 1 in specimens obtained during discectomy of the temporomandibular joint in patients with unilateral signs and symptoms of chronic closed lock (eight patients) and painful clicking (seven patients). Regarding the disc, aggrecan expression was higher in patients with chronic closed lock. As for the posterior disc attachment specimens, patients with chronic closed lock showed a tendency for higher expression of biglycan and hyaluronan synthase 1. The degradation of matrix in patients with chronic closed lock of the temporomandibular joint seems not to be caused by a reduced synthesis and the degenerative process seen in these patients is one with low turnover similar to the situation in primary osteoarthrosis of hyaline cartilage. The results indicate that any treatment should intervene early in the disease process of chronic closed lock in order to prevent the development of a degenerative process.

Accelerated osteoarthritis in the temporomandibular joint of biglycan/fibromodulin double-deficient mice

OBJECTIVE

To investigate whether the absence of biglycan and fibromodulin, two proteoglycans expressed in cartilage, bone and tendon, resulted in accelerated osteoarthritis in the temporomandibular joint (TMJ).

METHODS

Histological sections of TMJ from 3-, 6-, 9- and 18-month-old wild-type (WT) and biglycan/fibromodulin double-deficient (DKO) mice were compared. Immuno-stainings for biglycan, fibromodulin and proliferating cell nuclear antigen (PCNA) were performed.

RESULTS

Biglycan and fibromodulin were highly expressed in the disc and articular cartilage of the TMJ. At 3 months of age, both WT and DKO presented early signs of cartilage degeneration visible as small acellular areas under the articular surfaces and superficial waving. From 6 months of age, DKOs developed accelerated osteoarthritis compared to WT. At 6 months, small vertical clefts in the condylar cartilage and partial disruption of the disk were visible in the DKO. In addition, chondrocytes had lost their regular columnar organization to form clusters. At 9 months, these differences were even more pronounced. At 18 months, extended cartilage erosion was visible in DKOs when by comparison the thickness of the articular cartilage in WT controls was basically intact. PCNA staining was stronger in 3-month-old WT TMJ fibrocartilage than in 3-month-old DKO TMJ fibrocartilage suggesting that chondrocyte proliferation might be impaired in DKOs.

CONCLUSION

The biglycan/fibromodulin double knock-out mouse constitutes a useful animal model to decipher the pathobiology of osteoarthritis in the TMJ.

Modeling of Temporomandibular Joint Function Using MRI and Jaw-Tracking Technologies – Mechanics

The study of mechanics of the temporomandibular joint (TMJ) is important because its dysfunction and breakdown could be, at least partially, of mechanical origin. The incongruity of the articular surfaces of the TMJ is compensated by a fibrocartilaginous articular disc. Its dislocation and failure seem to be closely related to the development of osteoarthritis of the TMJ. The analysis of mandibular kinematics permits the detection and assessment of irregularities of TMJ function due to internal obstacles such as a displaced articular disc. Furthermore, the measurement of the dynamic relationship between the articular surfaces of the TMJ is useful to determine the strains undergone by the disc that if too high might compromise its integrity. The development of our research in TMJ mechanics has evolved from the acquisition of the traces of single mandibular points to an accurate and compact description of mandibular motion, in which the mechanical advantage of jaw muscles, and forces and torques acting on the jaw are considered as well. The combination of three-dimensional software models of TMJ anatomies obtained from MRI and jaw tracking with six degrees of freedom permits a subject-specific dynamic analysis of the intra-articular space, providing insight into individual disc deformation during function and TMJ loading. Studies performed with this system indicate that both TMJs are loaded during chewing, the balancing more so than the working joint. In fact, during chewing, the intra-articular distance is smaller for hard than for soft food, on closing than on opening, on the balancing than on the working side. This last finding is confirmed by static biting experiments, in which the condyle-fossa distance decreases more on the side contralateral to the bite force, depending on its magnitude. Also studies on the dynamics of compression areas indicate that plowing can occur through the disc during function, especially mediolaterally, due to stress field translation. This effect might contribute to cartilage wear and fatigue also because the disc is weaker mediolaterally. Further data indicate that the lateral area of the disc is mostly exposed to a higher mechanical energy density. This will be more intensively investigated using finite element method.

Type II collagen and aggrecan mRNA expressions in rabbit condyle following disc displacement

The aim of this investigation was to study the remodelling of cartilage in the mandibular condyle following disc displacement (DD) of the temporomandibular joint (TMJ). Forty adult Japanese white rabbits were used in this study. The right joints of 28 of the 40 rabbits had their discs surgically displaced. Four of the 28 were killed at 4 days or 1, 2, 4, 6, 8 and 12 weeks after surgery. The messenger RNA (mRNA) expression levels of aggrecan and type II collagen in cartilages were measured using in situ hybridization techniques. Results showed that aggrecan mRNA expression reduced in the first week after DD. The expression began to recover after 4 weeks and reached a normal level after 6 weeks. Type II collagen mRNA expression reduced from 4 weeks and the expression recovered after 8 weeks. This suggests that the chondrocyte reacting to the displacement of the TMJ disc, alters its matrix gene expression patterns and it is may be the cause of the shape changes of TMJ after DD.

A repetitive, steady mouth opening induced an osteoarthritis-like lesion in the rabbit temporomandibular joint

Although excessive mechanical stress is assumed to be one of the factors contributing to pathogenesis of temporomandibular joint (TMJ) osteoarthritis (OA), no pure mechanical-stress-induced OA model has been developed without surgical manipulation or puncture of the joint cavity. The purpose of this study was to establish a genuine mechanical-stress-induced OA model of the rabbit TMJ. In the experimental rabbits, repetitive, forced jaw-opening, 3 hrs/day for 5 days, was applied with the use of a general anesthesia protocol. By histological assessment of the TMJ articular tissues, partial eburnation of the articular cartilage, reactive marginal proliferation of the articular cartilage chondrocytes, and nested proliferation of chondrocytes in the subchondral bone area were observed at 7 days after the repetitive, forced-jaw-opening period. These results suggest that the repetitive, forced-jaw-opening protocol without surgical intervention can induce evident OA-like lesions in the rabbit TMJ, and this OA model may greatly contribute to the elucidation of the cartilage degradation mechanism in TMJ OA.

Chondrocyte apoptosis in temporomandibular joints with disc displacement

PURPOSE

We sought to study the presence of apoptosis in cartilage from rabbit temporomandibular joints with disc displacement (DD), and to examine the relationship between chondrocyte apoptosis and chondrocyte proliferation.

MATERIALS AND METHODS

Thirty Japanese white rabbits were used in this study. The right joints of 20 rabbits were subjected to surgical DD. Specimens were collected for study at 4 days and 1, 2, 4, and 6 weeks after surgery. Temporomandibular joints were studied by microscopy and in situ detection of apoptosis.

RESULTS

Experimental and sham surgery animals tolerated the surgical procedures well, and 16 of 20 of the surgically displaced discs were successful. A decrease in the number of chondrocytes in articular cartilage was observed after 2 weeks. Apoptotic chondrocytes were abundant in cartilage from DD joints. Apoptotic chondrocytes, most obvious at 1 or 2 weeks after surgery, were mostly found in the proliferative and hypertrophic zones. At 6 weeks after surgery, there were fewer apoptotic chondrocytes, but the cartilage layer was thinner than that of the control.

CONCLUSION

This study shows that chondrocyte apoptosis is increased in rabbit DD articular cartilage at early stage and that the apoptotic cells were localized predominantly in the proliferative and hypertrophic zones. Chondrocyte death may be of pathogenetic significance during cartilage repair in response to DD.

An experimental model of osteoarthrosis of the temporomandibular joint in monkeys

The purpose of this study was to develop a model of osteoarthrosis of the temporomandibular joint in monkeys, which is remarkably similar in structure and function to that of humans. Nine juvenile monkeys, two as controls and seven as an experimental group, were used in this study. In the experimental group, the articular eminence on both sides was surgically made steeper. Two animals were killed at 1 week, four at 6 months, and one at 1 year postoperatively and the temporomandibular joints were examined macroscopically and microscopically. Typical changes of osteoarthrosis were observed in the 6-month and 1-year specimens. These comprised clustering of chondrocytes which resulted in vertical and horizontal splitting in the articular cartilage, and fibrillation of the articular surface resulting in fibrous union in the joint cavity. These degenerative changes advanced progressively over time. Slight anterior displacement and degenerative changes in the articular disc were also seen.

Microscopic analysis of the temporomandibular joint in rabbits (Oryctolagus cuniculus L.) using an occlusal interference

The purpose of this study was to assess the tissue alterations in the temporomandibular joint (TMJ) of the New Zealand White rabbit (Oryctolagus cuniculus L.), after a unilateral occlusal interference insertion on the animal's right side back teeth. A total of 36 animals were used, thirty of which belonged to the experimental group and six to the control group. We established three experimental periods: 24 hours, three days and seven days. The control group animals were divided two by two; each pair followed the same experimental periods of the former one. The experimental group animals were submitted to the use of a 0.3 mm thick metallic cap with a visor. All animals were euthanized, and the TMJs were removed. Using a microscope for examination we observed, in all experimental periods, the presence of intra-articular hemorrhage in the supra- and infra-disk compartments as well as in the retro-disk zone. There were no inflammatory cells detected. The thickness of the condylar fibrocartilage presented significant alterations among the animals of the three experimental groups. In the left TMJs no inflammatory cells were detected. The results suggest that the insertion of a unilateral occlusal interference in rabbit back teeth does not cause any inflammatory intra-articular process within seven days; however, it does cause bilateral intra-articular hemorrhage and a larger compression of the condylar fibrocartilage in the joint opposite the side where the interference is placed. We also concluded that, in order to do research on the temporomandibular joint using animals, it is necessary have an independent (or separate) group of animals as controls.

A model for temporomandibular joint disc repositioning surgery

PURPOSE

The present study establishes a model of reversible anterior disc displacement using the rabbit craniomandibular joint (CMJ) and examines the period required for successful disc repositioning surgery.

MATERIALS AND METHODS

The left CMJ was exposed surgically in 27 animals and a suture positioned at the posterolateral portion of the disc was pulled in an anterior direction causing 7 mm of anterior disc displacement. The suture was then fixed to the zygomatic arch. The changes in the CMJ were observed microscopically in 3 rabbits each at 2, 3, 5, 8, and 24 weeks. Another 12 rabbits underwent secondary disc repositioning surgery either the second and third week after disc displacement, and then 3 rabbits from each group were assessed microscopically at 5 to 6 weeks and 21 to 22 weeks after the first operation. Ten rabbits had a sham operation, and 2 served as unoperated controls. Histomorphometric evaluation included changes in morphology, cartilage, and disc condition.

RESULTS

Progressive osteoarthritic change was induced by disc displacement. Articular disc perforation at 5 weeks after the first operation was accompanied by subchondral bone exposure. The CMJ morphology was almost normal in rabbits that underwent secondary disc repositioning 2 weeks after disc displacement. However, osteoarthritic changes and perforated discs similar to those in rabbits that did not undergo secondary disc repositioning were seen in animals in which repositioning was done in the third week.

CONCLUSION

Artificial disc displacement in the rabbit causes osteoarthritic changes are reversible when the displaced disc is restored within after 2 weeks but not at 3 weeks.

Viscoelastic properties of the human temporomandibular joint disc in patients with internal derangement

PURPOSE

This study investigated the viscoelastic properties of human temporomandibular joint (TMJ) discs in patients with severe internal derangement (ID).

PATIENTS AND METHODS

TMJ discs obtained from 5 patients with severe TMJ internal derangement were analyzed. Normal discs derived from 2 fresh cadavers and 4 patients without ID served as the controls. The viscoelastic responses of the discs to tensile forces were evaluated by means of stress-strain analyses.

RESULTS

The discs in both groups exhibited a nonlinear stress-strain relationship that was represented by a power function of the strain. However, after stress relaxation, the ID discs were likely to exhibit a linear stress-strain relationship. The instantaneous elastic moduli were almost the same in both discs, but the relaxed elastic modulus of the ID discs was significantly greater than that of the controls in lower strain range of less than 2%.

CONCLUSIONS

ID discs are more rigid than normal discs. These findings suggest that the changes in viscoelastic property of the discs in patients with ID are somewhat different from those that occur with aging.

Temporomandibular joint condyle changes after surgically induced non-reducing disk displacement in rabbits: a macroscopic and microscopic study

Experimentally induced displacement of the temporomandibular joint (TMJ) disk has previously been shown to induce shortening of the mandibular ramus on the ipsilateral side. The aim of this investigation was to reveal whether this shortening develops due to primary influence on condyle growth or by secondary loss of condyle mass due to degenerative tissue breakdown. Disk displacement was created in the right TMJ in seven 3-month-old rabbits, the posterior disk attachment kept intact. Seven rabbits underwent surgical opening of the TMJ without disk intervention. Seven additional animals served as references. After a 3-month experimental period, the animals were sacrificed. Previous analysis revealed shortening of mandibular height and length caused by ipsilateral TMJ disk displacement. The condyles were examined macroscopically and by histologic sectioning or scanning electron microscopy. All condyles were covered with smooth articulating soft tissue and without visible signs of degenerative changes. Four condyles from joints with disk displacement demonstrated substantial regressive remodeling resulting in a change of condyle shape with forward/downward rotation of an enlarged articulating surface. It was concluded that TMJ disk displacement in a growing individual can induce reduction of mandibular height and length before a stage where visible osteoarthrotic changes develop. It implies a primary adverse effect on condyle growth.

Clinical course of an antigen-induced arthritis model in the rabbit temporomandibular joint

The aim of this study was to investigate clinical features of an antigen-induced arthritis model in the rabbit temporomandibular joint (TMJ) and compare them to those in knee joint (KJ) arthritis. Eighteen adult male New Zealand White rabbits were divided into a TMJ arthritis group and a KJ arthritis group. Monoarthritis was induced unilaterally with ovalbumin and clinical observations, including joint swelling, skin surface temperature (SST) over the joints, and the withdrawal reflex threshold (WRT) to noxious pressure, were performed over a 3 week period. The joints were then evaluated histologically. The WRT was decreased during the 3 weeks after induction of TMJ arthritis, together with mild but significant joint swelling. The arthritic KJ also showed significant swelling and reduced WRT during the 3 week period. A significant increase of SST over the arthritic TMJ was present during the first week, while changes in SST over the KJ were inconsistent. The histological evaluation showed chronic arthritic features in all arthritic joints of both groups and no difference in the severity of arthritis was found between the TMJ and the KJ.

Whiplash injuries of the temporomandibular joint in motor vehicle accidents: speculations and facts

Referring to the temporomandibular joint (TMJ) of the human mandibular locomotor system, it has been asserted that displacement of the TMJ disc and inflammation of TMJ tissues are the results of acute and indirect trauma to the TMJ; on occasion this is allegedly experienced in motor vehicle accidents and commonly known as a TMJ whiplash injury. It is postulated that the TMJ whiplash injury is released in the occupant or occupants of a target vehicle when its rear end is impacted by the front end of a bullet vehicle. On the basis of detailed analyses of TMJ trauma/pain histories and TMJ magnetic resonance images, presented as circumstantial evidence in favour of the postulated TMJ whiplash injury, and detailed analyses of the mathematical biophysics of the mandibular locomotor system as well as direct experimental evidence, it is concluded that the postulated TMJ whiplash injury does not exist as a single and independent disease entity caused by motor vehicle accidents. If TMJ disc displacement and inflammation are present, they are expressions of an insidious and progressive pre-existing (pre-accident) disease entity that is comprised of TMJ synovitis/osteoarthritis (phase of inflammation with presence of immune system cells), TMJ internal derangement (phase of disc displacement and deformation with presence of proteinases), and TMJ osteoarthrosis (phase of degeneration with absence of immune system cells). For the asserted TMJ whiplash manoeuvre and ensuing injury to occur as postulated, the laws of physics and biology would have to be suspended.

Effect of postoperative diet on condylar cartilage response to discectomy

PURPOSE

Recent studies have shown that metabolic and structural changes occur in the condylar cartilage after surgical removal of the articular disc. There is some evidence that these structural changes are less pronounced in animals provisioned with a soft diet after disc removal. This study was initiated to assess whether a soft diet after discectomy in growing rats also results in alterations in the composition or metabolic activity of the matrix of the condylar cartilage.

MATERIALS AND METHODS

In two identical experiments, 28 thirty-day-old female Sprague-Dawley rats underwent unilateral surgical removal of the articular disc (discectomy) and were then provisioned with either a soft, mushy diet or a diet of normal rat pellets. When they were killed 3 weeks later, the condylar cartilages were removed, weighed, pulse-labeled in organ culture with [35S]-sulfate for 2 hours, and analyzed for sulfated glycosaminoglycan (GAG) content and [35S]-sulfate uptake.

RESULTS

As in previous studies, tissue weights and hydration were increased, and sulfated GAG content and [35S]-sulfate uptake decreased on the surgery side in animals fed a hard diet. Overall, fewer differences were present in the animals fed a soft diet, although tissue weights and hydration were still elevated on the discectomized side. Analysis of ratios of surgery/nonsurgery values in the hard diet versus the soft diet sample indicated that dietary consistency was a significant factor for tissue weights and [35S]-sulfate uptake, but not for hydration or sulfated GAG content.

CONCLUSIONS

These data suggest that discectomy exerts a more pronounced effect on growing animals fed a hard diet, although some changes also persist after discectomy in animals fed a soft diet.

Histochemical and immunohistochemical studies of the effects of experimental anterior disc displacement on sulfated glycosaminoglycans, hyaluronic acid, and link protein of the rabbit craniomandibular joint

PURPOSE

The purpose of this study was to determine the effects of surgically induced anterior disc displacement (ADD) on sulfated glycosaminoglycans (GAGs) such as keratan sulfate (KS), chondroitin-4-sulfate (C4S), and chondroitin-6-sulfate (C6S), hyaluronic acid (HA), and link protein (LP) of the rabbit craniomandibular joint (CMJ) using histochemical and immunohistochemical techniques.

MATERIALS AND METHODS

The right joint of 20 rabbits was exposed surgically, and all discal attachments were severed except for the posterior attachment. The disc was then repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control. Ten additional joints were used as nonoperated controls. Deeply anesthetized rabbits were perfused with 2% buffered formalin 2 weeks (10 rabbits) or 6 weeks (10 rabbits) after surgery. Discs, bilaminar zones, condyles, and articular eminences were excised. Condyles and articular eminences were decalcified in ethylenediaminetetraacetic acid (EDTA). All tissues were sectioned at 10 microns in a cryostat. Sections were incubated with alcian blue and monoclonal antibodies directed against KS, C4S, C6S, HA, or LP. After incubation in the appropriate fluorescein isothiocyanate (FITC)-labeled secondary antibodies, tissue sections were studied under the fluorescence microscope.

RESULTS

The results showed a reduction in alcian blue staining and KS, C4S, C6S, HA, and LP immunostaining in the disc and articular surfaces at 2 weeks after induction of ADD. This reduction was followed by an increase in their immunostaining at 6 weeks. Also, there was a progressive increase in alcian blue staining, and KS, C4S, C6S, and HA immunostaining in the bilaminar zone at 2 and 6 weeks.

CONCLUSION

It was concluded that surgical induction of ADD in the rabbit CMJ leads to alterations in KS, C4S, C6S, HA, and LP content, consistent with similar changes accompanying osteoarthritis of other synovial joints.

Identification of matrix metalloproteinases and their inhibitor in the articular disc of the craniomandibular joint of the rabbit

Connective tissue cells synthesize and secrete matrix metalloproteinases (MMPs), a family of matrix-degrading enzymes (comprising collagenases, gelatinases and stromelysins), which are capable of degrading all the constituent molecules of connective tissues at physiological pH. This investigation documents the synthesis and distribution of MMPs and their inhibitor TIMP-1 (tissue inhibitor of metalloproteinases-1) in the developing articular disc of the craniomandibular joint of the rabbit using indirect immunofluorescence microscopy. Cells of the disc synthesised all three classes of MMPs as well as TIMP-1 in all regions of the disc at all stages examined. MMPs and TIMP-1 were detected as bright intracellular accumulations probably within Golgi vesicles and as occasional diffuse, matrix-bound deposits. These results suggest that MMP-mediated matrix remodelling is a prominent feature of growth in craniomandibular joint disc.

Pathogenesis of degenerative joint disease in the human temporomandibular joint

The wide range of disease prevalences reported in epidemiological studies of temporomandibular degenerative joint disease reflects the fact that diagnoses are frequently guided by the presence or absence of non-specific signs and symptoms. Treatment is aimed at alleviating the disease symptoms rather than being guided by an understanding of the underlying disease processes. Much of our current understanding of disease processes in the temporomandibular joint is based on the study of other articular joints. Although it is likely that the molecular basis of pathogenesis is similar to that of other joints, additional study of the temporomandibular joint is required due to its unique structure and function. This review summarizes the unique structural and molecular features of the temporomandibular joint and the epidemiology of degenerative temporomandibular joint disease. As is discussed in this review, recent research has provided a better understanding of the molecular basis of degenerative joint disease processes, including insights into: the regulation of cytokine expression and activation, arachidonic acid metabolism, neural contributions to inflammation, mechanisms of extracellular matrix degradation, modulation of cell adhesion in inflammatory states, and the roles of free radicals and heat shock proteins in degenerative joint disease. Finally, the multiple cellular and molecular mechanisms involved in disease initiation and progression, along with factors that may modify the adaptive capacity of the joint, are presented as the basis for the rational design of new and more effective therapy.

An immunohistochemical study of the effects of surgical induction of anterior disc displacement in the rabbit craniomandibular joint on type I and type II collagens

The right craniomandibular joint (CMJ) was exposed surgically and all the discal attachments severed except for the posterior one. The disc was then repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control; 10 other joints were used as non-operated controls. Deeply anaesthetized rabbits were perfused with 2% buffered formalin 2 weeks (10 rabbits) or 6 weeks (10 rabbits) after the induction of the anterior disc displacement (ADD). The articular disc, bilaminar zone, mandibular condyle and articular eminence were excised. The condyles and the articular eminences were demineralized in EDTA. All tissues were then sectioned at 10 microns in a cryostat. Sections were incubated with polyclonal antibodies directed against type I or type II collagens. Following incubation in the appropriate fluorescein isothiocyanate-labelled secondary antibodies, these specimens were studied under the fluorescence microscope. At 2 weeks there was a reduction in type II collagen immunostaining; some areas of the experimental condylar cartilage showed a switch from type II to type I collagen. However, at 6 weeks there was an increase in type II collagen immunostaining and a decrease in type I compared to the 2-week group. It is concluded that surgical induction of ADD in the rabbit CMJ leads to alteration in the condylar cartilage collagen phenotype similar to that reported for osteoarthritic cartilage of other synovial joints.

Enlargement of the rabbit mandibular condyle after experimental induction of anterior disc displacement: a histomorphometric study

PURPOSE

Clinical and autopsy studies have shown that patients with temporomandibular joint dysfunction are more likely to have enlargement and deformity of the condyle and subsequently occlusal disharmony. However, it is not known what causes this enlargement. This study was designed to test the hypothesis that surgical induction of anterior disc displacement (ADD) in the rabbit craniomandibular joint (CMJ) could lead to enlargement and deformity of the condyle.

MATERIALS AND METHODS

The right CMJ was exposed surgically, and the discal attachments were severed except for the posterior discal attachment (bilaminar zone). Then, the disc was repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control. CMJ tissues then were removed after fixation at 24 hours (5 rabbits), 1 week (10 rabbits), 2 weeks (10 rabbits), or 6 weeks (10 rabbits), processed, and stained with hematoxylineosin. Histomorphometric assessment was used to evaluate changes in condylar volume, and thickness of the fibrous, reserve cell, and condylar cartilage layers.

RESULTS

The results showed a progressive enlargement of the condylar volume in all experimental joints compared with controls (P < .01). The enlargement was attributable to a significant increase in the cartilage thickness and surface area of the nonarticulating portion of the condyle in the 1-week group (P < .01). In the 2- and 6-week groups, there were significant, progressive increases in cartilage thickness and surface area of the articulating portion of the condyle (P < .01). In all animals, increased cartilage thickness was associated with a decrease in the thickness of the fibrous and the reserve cell layers (P < .01).

CONCLUSION

It is concluded that surgical induction of ADD in the rabbit CMJ causes enlargement of the condyle, which is in part caused by hyperplasia of the condylar cartilage.

Metabolic turnover of sulfated glycosaminoglycans and proteoglycans in rabbit temporomandibular joint cartilages with experimentally induced osteoarthrosis

Osteoarthrosis-like changes were induced by means of experimental disk perforation in the right temporomandibular joint of rabbits. The turnover of proteoglycans and glycosaminoglycans was studied 16 weeks later, using 35SO4. Tissues were sampled 1 day and 7 days after injection of the sulfate. The corresponding tissues from the left untreated joint were used as controls. After isolation of the glycosaminoglycans the incorporation of 35SO4 was estimated by scintillating counting. The extracted proteoglycans were analyzed, using gel electrophoresis, and the distribution of radioactivity was determined by autoradiography, followed by densitometry. Both the synthesis and rate of degradation of the proteoglycans were increased in the experimental disk, compared with those of the control. The net result of these metabolic changes seemed to be losses of small proteoglycans, whereas a slow increase in the number of larger ones may have occurred. The turnover rates of 4- and 6-sulfate increased, although their ratio remained unchanged at this stage of the osteoarthrosis-like process. In the condylar cartilage the turnover of large and small proteoglycans was also increased. The increase was most marked among those containing 6-sulfated galactosaminoglycans. The results concerning the experimental condylar cartilage indicated a decrease in the largest proteoglycan population, whereas the proportion of small proteoglycans was increased.