An animal model for studying mechanisms in human temporomandibular joint disc derangement

Comparing microstructural and micromechanical deformation of the TMJ disc in two anterior disc displacement models

OBJECTIVE

Anterior disc displacement (ADD) has been used to establish temporomandibular joint disorder (TMD) models. Based on whether preserve of the retrodiscal attachment, the modelling methodologies include ADD with dissecting the retrodiscal attachment (ADDwd) and ADD without dissecting the retrodiscal attachment (ADDwod). This article aims to determine which model better matches the micromechanical and microstructural progression of TMD.

METHODS

Through meticulous microscopic observations, the microstructure and micromechanical deformation of the TMJ discs in ADDwd and ADDwod rabbit models were compared at 2 and 20 weeks.

RESULT

Scanning electron microscopy and transmission electron microscopy showed that collagen fibres became slenderized and straightened, collagen fibrils lost diameter and arrangement in the ADDwd group at 2 weeks. Meanwhile, nanoindentation and atomic electron microscopy showed that the micro- and nano- mechanical properties decreased dramatically. However, the ADDwod group exhibited no significant microstructure and micromechanical deformations at 2 weeks. Dissection of the retrodiscal attachment contribute in the acceleration of disease progression at the early stage, the devastating discal phenotype remained fundamentally the same within the two models at 20 weeks.

CONCLUSION

ADDwod models, induced stable and persistent disc deformation, therefore, can better match the progression of TMD. While ADDwd models can be considered for experiments which aim to obtain advanced phenotype in a short time.

Effects of Glucosamine in the Temporomandibular Joint Osteoarthritis: A Review

Osteoarthritis in the temporomandibular joint (TMJ) is a chronic disease characterized by irreversible damage to articular surfaces, including inflammation, loss of articular cartilage, and subchondral bone alterations, which would be radiographically evident only in later stages. Symptomatic slow-acting so-called nutraceutical drugs have been proposed as a treatment for osteoarthritis in comparison to non-steroidal anti-inflammatory drugs (NSAID) because of their appreciable safety profile even in long-term intake. Glucosamine, being one among them, proved highly efficient in knee osteoarthritis. However, its application in TMJ osteoarthritis dates back only to 2001 and is still inconclusive in its efficiency even with systematic reviews, in restoring the structural and functional aspects of damaged TMJ. Glucosamine, being a natural compound and also a contributor to building the matrix of articular cartilage, can be utilized effectively for TMJ osteoarthritis as an adjunct along with other conventional treatment modalities available till now, which also have moderate prognosis in most of the clinical scenarios. This review summarizes data relating to the mechanism of osteoarthritis and its management using glucosamine formulations. The beneficial effects of glucosamine on the pathophysiology of TMJ osteoarthritis are possibly due to its contribution to hyaluronic acid regulation and in establishing a proper balance between anabolism/catabolism in the articular tissues.

Articular Disc of a Human Temporomandibular Joint: Evaluation through Light Microscopy, Immunofluorescence and Scanning Electron Microscopy

The extracellular matrix of the articular disc in a temporomandibular joint (TMJ) is composed mainly of collagen I and elastin. The collagen is important for resisting tensile forces, while the elastin is responsible to maintain the shape after deformation. We studied the orientation of collagen and elastin in a normal human temporomandibular joint disc by light microscopy, immunofluorescence and scanning electron microscopy. Our results demonstrated that collagen and elastin run parallel to each other in the intermediate zone with an anteroposterior orientation. From here, the orientation of two fibers groups changes into a disordered arrangement in the transition zone. Numerous elastic fibers cross with the collagen fibers, defining an interwoven knitted arrangement. The evaluation of the disc-condyle relationship shows that the medial margin of the articular disc is inserted directly at the superficial layer of the mandibular condylar cartilage. Therefore, the tensile properties of the TMJ disc are expressed in the directions corresponding to the orientation of the collagen fibers, and the complex orientation of elastin with the collagen determines the maintaining of the shape after the stresses by the joint movements. Moreover, the direct anatomical relationship between the articular disc and the mandibular condyle makes a decisive contribution to the understanding of TMJ movements.

Reduction of osteoarthritis severity in the temporomandibular joint of rabbits treated with chondroitin sulfate and glucosamine

Osteoarthritis is a degenerative disease that causes substantial changes in joint tissues, such as cartilage degeneration and subchondral bone sclerosis. Chondroitin sulfate and glucosamine are commonly used products for the symptomatic treatment of osteoarthritis. The aim of the present study was to investigate the effects of these products when used as structure-modifying drugs on the progression of osteoarthritis in the rabbit temporomandibular joint. Thirty-six New Zealand rabbits were divided into 3 groups (n = 12/group): control (no disease); osteoarthritis (disease induction); and treatment (disease induction and administration of chondroitin sulfate and glucosamine). Osteoarthritis was induced by intra-articular injection of monosodium iodoacetate. Animals were killed at 30 and 90 days after initiation of therapy. The treatment was effective in reducing disease severity, with late effects and changes in the concentration of glycosaminoglycans in the articular disc. The results indicate that chondroitin sulfate and glucosamine may have a structure-modifying effect on the tissues of rabbit temporomandibular joints altered by osteoarthritis.

A rat model for inducing temporomandibular anterior disc displacement experimentally

The aim of this study was to establish an experimental rat model of temporomandibular joint (TMJ) anterior disc displacement (ADD). A pilot study was conducted to determine the most appropriate surgical protocol. In the main experiment, 40 rats were used. Twenty-four rats were subjected to ADD in the right TMJ, and subsequently thereafter six, nine, and nine rats were sacrificed at 1, 4, and 8 weeks, respectively, for gross evaluation. Twelve rats that underwent a sham operation were equally divided and sacrificed at each of the above time points. Four non-treated control rats were sacrificed at the beginning of the study. TMJ blocks were harvested for radiological and histological assessment. Gross examination showed that 14 rats in the ADD group (58.3%) had anterior displacement of the TMJ disc. In the ADD joints, posterior condylar cartilage thickness decreased during the follow-up period; however, there was no significant difference between the sham-treated and ADD joints, or among the follow-up time points (P > 0.05). The anterior condylar cartilage exhibited obvious qualitative alterations. Radiologic signs of osteoarthrosis appeared after ADD surgery, but this became attenuated with time. The model investigated in this study successfully induced ADD in rats, and should be useful for assessment of progressive changes in the TMJ following ADD.

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.

Scaffold-Based Temporomandibular Joint Tissue Regeneration in Experimental Animal Models: A Systematic Review

Reconstruction of degenerated temporomandibular joint (TMJ) structures remains a clinical challenge. Tissue engineering (TE) is a promising alternative to current treatment options, where the TMJ is either left without functional components, or replaced with autogenous, allogeneic, or synthetic grafts. The objective of this systematic review was to answer the focused question: in experimental animal models, does the implantation of biomaterial scaffolds loaded with cells and/or growth factors (GFs) enhance regeneration of the discal or osteochondral TMJ tissues, compared with scaffolds alone, without cells, or GFs? Following PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analysis) guidelines, electronic databases were searched for relevant controlled preclinical in vivo studies. Thirty studies reporting TMJ TE strategies in both small (rodents, rabbits; n = 25) and large animals (dogs, sheep, goats; n = 5) reporting histological and/or radiographic outcomes were included. Twelve studies reported ectopic (subcutaneous) implantation models in rodents, whereas 18 studies reported orthotopic, surgically induced defect models in large animals. On average, studies presented with an unclear-to-high risk of bias. In most studies, mesenchymal stem cells or chondrocytes were used in combination with either natural or synthetic polymer scaffolds, aiming for either TMJ disc or condyle regeneration. In summary, the overall preclinical evidence (ectopic [n = 6] and orthotopic TMJ models [n = 6]) indicate that addition of chondrogenic and/or osteogenic cells to biomaterial scaffolds enhances the potential for TMJ tissue regeneration. Standardization of animal models and quantitative outcome evaluations (biomechanical, biochemical, histomorphometric, and radiographic) in future studies, would allow more reliable comparisons and increase the validity of the results.

Bilateral TMJ Disk Displacement Induces Mandibular Retrognathia

Unilateral non-reducing TMJ disk displacement has been shown to retard mandibular growth on the ipsilateral side, with facial asymmetry a sequela. We hypothesized that bilateral affliction would impair mandibular growth bilaterally, generating mandibular retrognathia. Non-reducing TMJ disk displacement was surgically created in 10 growing New Zealand White rabbits. Ten additional rabbits served as a sham-operated control group. Facial growth was followed in serial cephalograms, with tantalum implants, during a period corresponding to childhood and adolescence in man. The results verified that bilateral non-reducing TMJ disk displacement retarded mandibular growth bilaterally, the extent corresponding to mandibular retrognathia in man. Maxillary growth was also retarded, but to a lesser degree. Growth impairment fluctuated over time, the most striking retardation occurring during periods of general growth acceleration. This should be taken into consideration when orthodontic treatment, aimed at stimulating mandibular growth, is initiated in adolescent individuals with non-reducing TMJ disk displacement.

Tensile biomechanical properties of human temporomandibular joint disc: Effects of direction, region and sex

Approximately 30% of temporomandibular joint (TMJ) disorders include degenerative changes to the articular disc, with sex-specific differences in prevalence and severity. Limited tensile biomechanical properties of human TMJ discs have been reported. Stress relaxation tests were conducted on TMJ disc specimens harvested bilaterally from six males and six females (68.9±7.9 years), with step-strain increments of 5%, 10%, 15%, 20% and 30%, at 1% strain-per-second. Stress versus strain plots were constructed, and Young׳s Modulus, Instantaneous Modulus and Relaxed Modulus were determined. The effects of direction, region, and sex were examined. Regional effects were significant (p<0.01) for Young׳s Modulus and Instantaneous Modulus. Anteroposteriorly, the central region was significantly stiffer than medial and lateral regions. Mediolaterally, the posterior region was significantly stiffer than central and anterior regions. In the central region, anteroposteriorly directed specimens were significantly stiffer compared to mediolateral specimens (p<0.04). TMJ disc stiffness, indicated by Young׳s Modulus and Instantaneous Modulus, was higher in directions corresponding to high fiber alignment. Additionally, human TMJ discs were stiffer for females compared to males, with higher Young׳s Modulus and Instantaneous Modulus, and female TMJ discs relaxed less. However, sex effects were not statistically significant. Using second-harmonic generation microscopy, regional collagen fiber organization was identified as a potentially significant factor in determining the biomechanical properties for any combination of direction and region. These findings establish structure-function relationships between collagen fiber direction and organization with biomechanical response to tensile loading, and may provide insights into the prevalence of TMJ disorders among women.

Viscoelastic shear properties of porcine temporomandibular joint disc

OBJECTIVES

To investigate the intrinsic viscoelastic shear properties in porcine TMJ discs.

MATERIALS AND METHODS

Twelve fresh porcine TMJ discs from young adult pigs (6-8 months) were used. Cylindrical samples (5 mm diameter) with uniform thickness (~1.2 mm) were prepared from five regions of the TMJ disc. Torsional shear tests were performed under 10% compressive strain. Dynamic shear was applied in two methods: 1) a frequency sweep test over the frequency range of 0.1-10 rad/s with a constant shear strain amplitude of 0.05 rad and 2) a strain sweep test over the range of 0.005-0.15 rad at a constant frequency of 10 rad/s. Transient stress relaxation tests were also performed to determine the equilibrium shear properties.

RESULTS

As the frequency increased in the frequency sweep test, the dynamic shear complex modulus increased, with values ranging from 7 to 17 kPa. The phase angle, ranging from 11 to 15 degrees, displayed no pattern of regional variation as the frequency increased. The dynamic shear modulus decreased as the shear strain increased. The equilibrium shear modulus had values ranging from 2.6 to 4 kPa. The posterior region had significantly higher values for dynamic shear modulus than those in the anterior region, while no significant regional difference was found for equilibrium shear modulus.

CONCLUSION

Our results suggest that the intrinsic region-dependent viscoelastic shear characteristics of TMJ disc may play a crucial role in determining the local strain of the TMJ disc under mechanical loading.

Fibrochondrocyte Growth and Functionality on TiO₂ Nanothin Films

Disorders affecting the temporomandibular joint (TMJ) are a long-standing health concern. TMJ disorders (TMJD) are often associated with an internal disc derangement accompanied by a suite of symptoms including joint noises, jaw dysfunction, and severe pain. The severity of patient symptoms and their reoccurrence can be alleviated to some extent with conservative therapy; however, refractory cases often require surgery that has shown only limited success. Bioengineered scaffolds with cell supportive surfaces an d nanoarchitectures that mimic TMJ tissue structure may offer an alternative treatment modality. In this study, titanium dioxide (TiO₂) nanothin films, fabricated by layer-by-layer assembly, were examined as means for creating such a scaffold. The viability and growth of TMJ discal fibrochondrocytes (FCs) were assessed through MTT and DNA assays and total protein content over a 14-day experimental period. ELISA was also used to measure expression of types I and II collagen, decorin and aggrecan. Quantitative analyses demonstrated that FCs synthesized characteristic discal matrix proteins, with an increased production of type I collagen and decorin as opposed to collagen type II and aggrecan. A stimulatory effect on discal FC proliferation and extracellular matrix (ECM) expression with thicker nanofilms was also observed. The cumulative results suggest that TiO₂ nanofilms may have potential as a TMJ scaffolding material.

Rabbit model for osteoarthrosis of the temporomandibular joint as a basis for assessment of outcomes after intervention

Osteoarthritis can be induced in the temporomandibular joint (TMJ) by primary or secondary trauma, or overloading of the joint. We have therefore systematically evaluated the histological progression of experimental osteoarthritis induced by a high concentration of monosodium iodoacetate into the rabbit TMJ. These findings may contribute to the establishment of a protocol to investigate the benefits of treatment of osteoarthritis of the TMJ. We used 21 male New Zealand rabbits; the 15 in the test group were given an intra-articular injection of monosodium iodoacetate 10mg/ml into the right TMJ and were killed after 60 (n=5), 80 (n=5), and 100 days (n=5). The six in the control group were given an injection of saline into the right TMJ. The assessment system for osteoarthritis based on six grades was used for the histological analysis of severity. The model was effective in producing histological changes in the cartilage consistent with those found in osteoarthritis at all time points. The within-group analysis indicated that the disease did not progress after 60 days. The successful induction of osteoarthritis in this way, its stabilisation after 60 days, and the appropriate size of the animal suggest that this experimental model is ideal for future studies of the effectiveness of treatment in osteoarthritis of the TMJ.

Biomechanical and biochemical outcomes of porcine temporomandibular joint disc deformation

OBJECTIVE

The structure-function relationship in the healthy temporomandibular joint (TMJ) disc has been well established, however the changes in dysfunctional joints has yet to be systematically evaluated. Due to the poor understanding of the etiology of temporomandibular disorders (TMDs) this study evaluated naturally occurring degenerative remodeling in aged female porcine temporomandibular joint (TMJ) discs in order to gain insight into the progression and effects on possible treatment strategies of TMDs.

DESIGN

Surface and regional biomechanical and biochemical properties of discal tissues were determined in grossly deformed (≥Wilkes Stage 3) and morphologically normal (≤Wilkes Stage 2) TMJ discs.

RESULTS

Compared to normal disc structure the deformed discs lacked a smooth biconcave shape and characteristic ECM organization. Reduction in tensile biomechanical integrity and increased compressive stiffness and cellularity was found in deformed discs. Regionally, the posterior and intermediate zones of the disc were most frequently affected along with the inferior surface.

CONCLUSIONS

The frequency of degeneration observed on the inferior surface of the disc (predominantly posterior), suggests that a disruption in the disc-condyle relationship likely contributes to the progression of joint dysfunction more than the temporodiscal relationship. As such, the inferior joint space may be an important consideration in early clinical diagnosis and treatment of TMDs, as it is overlooked in techniques performed in the upper joint space, including arthroscopy and arthrocentesis. Furthermore, permanent damage to the disc mechanical properties would limit the ability to successfully reposition deformed discs, highlighting the importance of emerging therapies such as tissue engineering.

Radiological follow-up results of untreated anterior disc displacement without reduction in adults

The aim of this study was to assess the radiographic changes in untreated adults with bilateral anterior disc displacement without reduction. A cohort study was designed to compare the bone changes, effusion, disc configuration, and pseudo-disc changes on two magnetic resonance images obtained at least 24 months apart. Twenty-eight patients (22 female, six male) with a mean age of 33.1 years (range 20-57 years) were included. The mean interval between the initial visit and the follow-up visit was 36.2 months. At the initial visit, the frequencies of bone changes, effusion, disc deformation, and pseudo-disc changes were 51.79%, 35.71%, 100%, and 0%, respectively. At follow-up, the frequency of effusion had decreased significantly. The frequency of bone changes had increased significantly to 75%, but newly formed cortical bone was present in five condyles. All discs remained deformed. Pseudo-disc changes were detected in five joints. Over a long period of observation, there was a significant decrease in effusion and a significant increase in bone changes. However, some adaptive changes occurred.

Disc positions and condylar changes induced by different stretching forces in the model for anterior disc displacement of temporomandibular joint

OBJECTIVE

The aim of this study was to compare the disc positions and condylar changes induced by different stretching forces in the modified animal model for anterior disc displacement (ADD) of the temporomandibular joint.

METHODS

In the experimental group, 30 rabbits were equally divided into 3 subgroups and underwent surgical ADD via different stretching forces: group A with 0.5 N, group B with 1 N, and group C with 2 N. In the sham group, 6 rabbits underwent the same surgery without the disc being pulled anteriorly. The diagnosis of ADD was made when the anterior band of the disc was located anteriorly to the articular eminence. Histologic and radiographic changes of the condyles were observed under light microscopy and micro-computed tomography scanning 1 week after surgery.

RESULTS

The success rates of ADD were both 100% in groups B and C and 70% in group A. The correlations between the stretching force and severity of ADD, the stretching force and severity of cartilage changes, and the severity of ADD and cartilage changes were statistically significant (P < 0.01). The most advanced ADD and severest condylar changes were induced in group C. Condylar remodeling and scleroses were found in micro-computed tomography scans.

CONCLUSIONS

The rabbit model for ADD has been successfully established in this study, which is feasible and minimally invasive. The stretching force of at least 1 N could induce the disc displaced successfully. Larger stretching force would induce severer ADD and condylar degenerative changes.

Immortalization and characterization of mouse temporomandibular joint disc cell clones with capacity for multi-lineage differentiation

OBJECTIVE

Despite the importance of temporomandibular joint (TMJ) disc in normal function and disease, studying the responses of its cells has been complicated by the lack of adequate characterization of the cell subtypes. The purpose of our investigation was to immortalize, clone, characterize and determine the multi-lineage potential of mouse TMJ disc cells.

DESIGN

Cells from 12-week-old female mice were cultured and immortalized by stable transfection with human telomerase reverse transcriptase (hTERT). The immortalized cell clones were phenotyped for fibroblast- or chondrocyte-like characteristics and ability to undergo adipocytic, osteoblastic and chondrocytic differentiation.

RESULTS

Of 36 isolated clones, four demonstrated successful immortalization and maintenance of stable protein expression for up to 50 passages. Two clones each were initially characterized as fibroblast-like and chondrocyte-like on the basis of cell morphology and growth rate. Further the chondrocyte-like clones had higher mRNA expression levels of cartilage oligomeric matrix protein (COMP) (>3.5-fold), collagen X (>11-fold), collagen II expression (2-fold) and collagen II:I ratio than the fibroblast-like clones. In contrast, the fibroblast-like clones had higher mRNA expression level of vimentin (>1.5-fold), and fibroblastic specific protein 1 (>2.5-fold) than the chondrocyte-like clones. Both cell types retained multi-lineage potential as demonstrated by their capacity to undergo robust adipogenic, osteogenic and chondrogenic differentiation.

CONCLUSIONS

These studies are the first to immortalize TMJ disc cells and characterize chondrocyte-like and fibroblast-like clones with retained multi-differentiation potential that would be a valuable resource in studies to dissect the behavior of specific cell types in health and disease and for tissue engineering.

Effect of mechanical strain on solute diffusion in human TMJ discs: an electrical conductivity study

This study investigated the effect of mechanical strain on solute diffusion in human TMJ discs (mean cadaver age 77.8) using the electrical conductivity method. The electrical conductivity, as well as small ion diffusivity, of male and female TMJ discs was determined under three compressive strains. In the male group, the average disc electrical conductivity (mean ± SD) at 0% strain was 5.14 ± 0.97 mS/cm, decreased to 4.50 ± 0.91 mS/cm (-12.3%) at 10% strain, and 3.93 ± 0.81 mS/cm (-23.5%) at 20% compressive strain. Correspondingly, the average disc relative ion diffusivity at 0% strain was 0.44 ± 0.08, decreased to 0.40 ± 0.08 (-8.9%) at 10% strain, and 0.36 ± 0.08 (-16.7%) at 20% compressive strain. In the female group, the average disc electrical conductivity at 0% strain was 5.84 ± 0.59 mS/cm, decreased to 5.01 ± 0.50 mS/cm (-14.2%) at 10% strain, and 4.33 ± 0.46 mS/cm (-25.8%) at 20% compressive strain. Correspondingly, the average disc relative ion diffusivity at 0% strain was 0.49 ± 0.05, decreased to 0.43 ± 0.04 (-11.3%) at 10% strain, and 0.39 ± 0.04 (-19.9%) at 20% compressive strain. The results indicated that mechanical strain significantly impeded solute diffusion through the disc. This mechanical strain effect was larger in the female than in the male human TMJ disc. This study may provide new insights into TMJ pathophysiology.

Synovial tissue in internal derangement of temporomandibular joint

The aim of this study was to examine the changes of the synovial tissue in rabbit temporomandibular joint (TMJ) internal derangement (ID) models using light and electron microscope. Thirteen rabbits were included in our study. The right TMJ of all animals were used as the experimental group while the left ones as the control group. ID model was established by using elastic rubber rope to stretch anteriorly. Synovial tissues were collected and examined by light and electron microscope to observe microstructure and ultrastructure changes after establishing the model. CD34 was used to count small blood vessels. A paired t test was performed with SPSS 16.0 software package to compare the data of the experimental and the control side. The average number of small blood vessels in the experimental side was significantly greater than the control side both in the first and second week. Numerous synovial cells of type A and type B were detected under electron microscope, and type A cells shrunk after a period of time. This study is helpful to understand the development of the TMJ intra-articular adhesion.

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.

Usefulness of cone beam computed tomography in temporomandibular joints with soft tissue pathology

OBJECTIVE

the aim of the study was to evaluate the usefulness of cone beam CT (CBCT) in temporomandibular joints (TMJs) with soft tissue pathology.

METHODS

106 TMJs of 55 patients with temporomandibular disorder (TMD) were examined by MRI and CBCT. MR images were used for the evaluation of disc displacement, disc deformity, joint effusion and obscurity of temporal posterior attachment (TPA). CBCT images were evaluated for the presence or absence of osseous abnormalities. The chi(2) test was used to analyse the association between MRI and CBCT findings.

RESULTS

MRI of 106 TMJs revealed disc displacement, disc deformity, joint effusion and obscurity of the TPA in 68, 73, 28 and 27 joints, respectively. Of the 68 TMJs with disc displacement, anterior disc displacement without reduction (ADDWR) was seen most frequently (47/68). CBCT imaging found 65 TMJs were characterized by the presence of osseous abnormalities and were significantly associated with disc deformity and ADDWR (P < 0.05). There was no statistically significant association between the presence of joint effusion and obscurity of TPA and TMJ osseous abnormalities.

CONCLUSIONS

TMD patients with confirmed ADDWR or disc deformity on MRI are at risk of having osseous abnormalities in the TMJ and further examination with CBCT is recommended.

Quantitative analysis of the elastic fibres in the human temporomandibular articular disc and its attachments

A quantitative study of the elastic fibres found in the human temporomandibular disc and its attachments was performed. Seven left discs from 57- to 82-year-old subjects, without macroscopic evidence of a TMJ disorder, were analysed and prepared in parasagittal sections. The surface amount was measured, thresholded and expressed from 0 to 1, using microscopic digitized views after Weigert's resorcin-fuchsin staining of elastic fibres. Fibre density rates ranged from 0 to 0.687. The mean density was 0.1532 (sigma=0.1150) in the upper bilaminary zone, 0.1097 (sigma=0.1159) in the lower bilaminary zone, 0.0474 (sigma=0.0782) in the anterior band, 0.0180 (sigma=0.0603) in the posterior band and null in the intermediate zone. The difference in density rate between the structures was significant, except for the posterior band and the intermediate zone. The elastic fibre density rates in central and medial locations of the upper and lower bilaminary zones were twice as big as in the lateral locations. In the anterior band, the elastic fibre density was less abundant medially than in its lateral part. These quantitative results support the current elastic fibre distribution scheme, and confirm the necessity of studying their orientation, taking into account age and temporomandibular joint health parameters.

The treatment of painful temporomandibular joint clicking with oral splints

BACKGROUND

The authors compared the efficacy of bilateral balanced and canine guidance (occlusal) splints in the treatment of temporomandibular joint (TMJ) pain in subjects who experienced joint clicking with a nonoccluding splint in a double-blind, controlled randomized clinical trial.

METHODS

The authors randomly assigned 57 people with signs of disk displacement and TMJ pain into three groups according to the type of splint: bilateral balanced, canine guidance and nonoccluding. The authors followed the groups for six months using analysis of a visual analog scale (VAS), palpation of the TMJ and masticatory muscles, mandibular movements and joint sounds. They used repeated analysis of variance and a chi(2) test to test the hypothesis.

RESULTS

The type of guidance used did not influence the pain reduction, yet both occlusal splints were superior to the nonoccluding splint, on the basis of the VAS. Despite similar outcomes in relation to opening, left lateral and protrusive movements, TMJ and muscle pain on palpation, subjects who used the occlusal splints had improved clinical outcomes. The frequency of joint noises decreased over time, with no significant differences among groups. Subjects in the groups using the occlusal splints reported more comfort.

CONCLUSION

The type of lateral guidance did not influence the subjects' improvement. All of the subjects had a general improvement on the VAS, though subjects in the occlusal splint groups had better results that did subjects in the nonoccluding splint group.

Partial time use of anterior repositioning splints in the management of TMJ pain and dysfunction: a one-year controlled study

This study aimed at evaluating the effectiveness of partial use of anterior repositioning appliances in the management of TMJ pain and dysfunction when compared to stabilization splints and a control group in a one-year follow-up. Sample was initially constituted by 60 patients, randomly divided into three groups: I- stabilization splints, II- repositioning splints and III- no treatment. The whole sample was evaluated by means of TMJ and muscle palpation, mandibular AROM, analysis of occlusal contacts, joint sounds inspection and Visual Analogue Scale (VAS) for one year; 52 patients composed the final sample. A significant (after 15 days) improvement in pain report (VAS) and palpation index was found for group II (p<0.01). The occurrence of occlusal alterations as posterior open bite or gross interferences after the splint therapy and increased muscle tenderness were not problems in this study. Similar results in joint noises reduction were observed for the entire sample. It was concluded that controlled partial use of repositioning splints is a beneficial tool in the management of intra-articular pain and dysfunction, with no risks of irreversible occlusal changes.

Histologic evaluation of temporomandibular arthritis induced by mild mechanical loading in rabbits

BACKGROUND

We still lack knowledge of causative factors in arthritis related to temporomandibular disorders (TMD). The goal of the present study was to investigate whether applying a mechanical loading on the glenoid fossa can induce arthritis.

METHODS

Coil springs were placed in 24 rabbits so as to exert a force of 100 g between the orbital edge and the antegonial notch. At 1, 2, 4 and 8 weeks after the surgery, six samples of the temporomandibular joint (TMJ) were removed for histologic examination.

RESULTS

The results showed that mild synovitis began 1-2 weeks after the start of loading, and the degree of synovitis was significant at 4 weeks, and that morphologic changes occurred in the articular eminence and condyle, while type II collagen in the cartilage of the articular eminence degraded prior to that in the condyle.

CONCLUSIONS

Our results revealed that mild, continuous mechanical loading to the glenoid fossa induces synovitis of the articular capsule, and induces organic changes of the articular cartilage without destroying these tissues.

The prevalence of osteoarthrosis in cases of advanced internal derangement of the temporomandibular joint: a clinical, surgical and histological study

INTRODUCTION

The articular disk has a central role in the pathology of internal derangement of the Temporomandibular Joint (TMJ). What is less clear is the role of osteoarthrosis in the development of internal derangement. The aim of this study is to determine the prevalence of osteoarthrosis in cases of advanced and recalcitrant TMJ internal derangement that were treated by diskectomy.

MATERIALS AND METHODS

This study involved 22 joints in 18 patients who underwent surgery for the treatment of advanced and recalcitrant internal derangement of the TMJ. All patients included in the study failed to respond to at least 6 months of pre-operative conservative treatment and the clinical diagnoses of advanced TMJ internal derangement were confirmed on pre-operative MRI's. Tissue specimens were obtained from all 22 joints for histopathology. The specimens included articular disks that were excised from all 22 joints which were found to have severely displaced and deformed disks that were judged to be irreparable at the time of surgery. Also included were eight tissue samples from the mandibular condyles that were judged to be diseased on pre-operative tomograms and at the time of surgery. All samples were prepared in serial sections in the standard way and examined under light microscopy by two experienced Oral Pathologists.

RESULTS

There were 22 specimens of articular disk examined together with 8 specimens from the mandibular condyle. All 22 joints (100%) showed histological evidence of disk pathology and eight of the 22 joints (34.4%) were found to have condylar pathology. The most common disk pathology was hyalinization indicative of disk degeneration (12/22). The most common condylar pathology found was articular surface degeneration indicative of osteoarthrosis (8/22).

CONCLUSION

The clinical and radiological diagnoses of advanced TMJ internal derangement correlated with histological findings of degeneration and inflammation of the articular disk in all 22 specimens. The 8 specimens obtained from the condylar head showed histological features consistent with osteoarthrosis. This study showed that osteoarthrosis and internal derangement were found to co-exist in the same joint in about one-third of cases. The fact that osteoarthrosis was not found in all cases suggests that perhaps the widely held view that subclinical osteoarthrosis may lead to pathologic tissue responses in the form of internal derangement will need to be re-examined.

Morphologic changes in the TMJ following splint wear

Intraoral splints are a commonly used dental treatment for a variety of conditions. Because such splints alter the condyle-disc-fossa relationship, they probably change the loading status of the temporomandibular joint (TMJ), including the TMJ disc. Collagen, a major constituent of the disc, acts to resist tensile loading, and it is presumed that the fiber orientations of the individual disc bands reflect their functional loading. Therefore, the purpose of this study was to examine effects of intraoral splint wear on TMJ morphology in general, and collagen orientation of the intra-articular disc in particular. Young adult, female miniature pigs were divided into three groups: open-bite splint, protrusive-bite splint, and unsplinted control. Splints were worn for 2 months, after which the TMJ discs were harvested for histological examination and stereological analysis, and the skulls were cleaned. Although the splints had no effect on skull dimensions, changes were seen in the TMJs. The discs of the protrusively-splinted group showed an increased thickness of the posterior band (P < 0.015) and minor changes in collagen orientation of the anterior band. The most striking change was the presence of a degenerative osseous defect on the medial side of the mandibular condyle in half of the splinted animals. These results indicate that prolonged splint wear can induce remodeling and even injury of TMJ tissues.

Viscoelastic properties and residual strain in a tensile creep test on bovine temporomandibular articular discs

This study was designed to evaluate the creep characteristics and residual strain of bovine temporomandibular joint (TMJ) discs in tension. Twenty discs were divided into three specimens each: central, lateral and medial regions. Tension of 1.0 MPa was applied and sustained for 20 min to the specimens from 10 right-side discs, and tension of 1.5 MPa to specimens from 10 left-side discs. After the period of tension for creep, the specimens were removed from the tension devices and restoration observed for 20 min. Time-dependent creep curves showed a marked change in strain during the initial 5s. The essential time delay in strain ceased after 2 min, and strain reached an almost steady level after 3 min. At a tensile stress of 1.5 MPa, a strain of 14.5% on average was produced after 20 min creep in the central specimens; peripheral specimens showed strains of 12.4% on average. There were significant differences in strain between the central and peripheral specimens. The residual strain after 20 min restoration was 0.93% on average and there were no significant regional differences. This creep feature could be well represented by a generalized linear viscoelastic model. It was concluded that the regional differences in viscoelasticity might be caused by the complicated articulating functions of the TMJ, and that the residual strain caused by sustained stress could be an important factor in disc deformation.

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.

Fibrous adhesions in the joint compartment of the temporomandibular joint associated with experimental opposite drawing mandibular ramus in rabbit

The purpose of this study was to develop a rabbit model of fibrous adhesions in the joint compartment of the temporomandibular joint (TMJ) without surgical invasion into the joint compartment. A unilaterally elastic force of about 120 grams was applied from the anterior edge of masseteric tuberosity to the posterior part of the zygomatic arch between the masseteric fascia layer and the subcutaneous layer in 14 rabbits. The blocks of nondrawing side TMJ were removed after four weeks. Fibrous adhesions were observed in 13 rabbits except for one rabbit that lost over 30% of its body weight. In eight of the rabbits, the adhesions were detected in both joint compartments. This animal model for fibrous adhesion of the TMJ will be useful in understanding the pathogenesis of adhesion in human TMJs.

Age changes in the cells of the intra-articular disc of the temporomandibular joints of rats and marmosets

Cells in the intra-articular disc of the temporomandibular joint were studied ultrastructurally at three different ages to investigate any age changes. Rats aged 2, 15.5 months, and 2.5 years, and marmosets aged 21 months, 7 years, and between 10.5 and 14 years were studied. In the first two age groups of the rat and the first of the marmoset, the cells were generally rounded and had moderate amounts of rough endoplasmic reticulum and other organelles associated with protein synthesis and secretion. Many cells had conspicuous amounts of microfilamentous material and cell membranes were closely applied to the collagen fibrils of the extracellular matrix. Occasionally, a narrow, irregular space containing microfilamentous material lay adjacent to the cell membrane. In the 2.5-year-old rats and the two older age groups of marmosets, cells with chondrocyte-like morphology were present. These cells were surrounded by a conspicuous pericellular matrix devoid of collagen fibrils and composed of microfilamentous material embedded in an amorphous ground substance. They resembled cells described in fibrocartilage from other sites, but differed from chondrocytes in hyaline cartilage by lacking a pericellular capsule. Thus, rats and marmosets both show cellular age changes in the intra-articular disc of the mandibular joint, which can be considered as changing from fibrous to fibrocartilaginous with age, a condition similar to that reported in humans.

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.

Effects of intraoral splint wear on proteoglycans in the temporomandibular joint disc

Intraoral splints are a common dental treatment for dysfunctions of the temporomandibular joint (TMJ), but their effects on the structures of the joint, specifically the disc, have not been well investigated. This study examined proteoglycans (PGs) of the TMJ disc of the miniature pig and tested for alterations resulting from intraoral splint wear. Sixteen female pigs were divided into three groups: control (C), control splint (CS), and protrusive splint (PS). Splinted groups received chrome-cobalt ramp splints which were worn continuously for 2 months. PG content within various disc locations was determined by colorimeteric assay. PG synthesis and type were examined by labeling with (35)S-sulfate and SDS-PAGE analysis. Average water content of the disc was 77.1%, which places it at the high end of the normal range for collagenous biomaterials (60-80%). PGs migrating to the positions typical of aggrecan, biglycan, and decorin on SDS-PAGE were present in all locations of all groups. The highest content and synthesis of PGs were always found in the intermediate band of the disc regardless of group (P < 0.05), supporting the notion that this band encounters heavy compressive loading during function. The joints of animals from both splinted groups showed a high frequency of gross pathology. Biglycan synthesis was increased in both splinted groups (P < 0.05). Newly synthesized biglycan had a shorter migration distance in the intermediate bands of the CS group, suggesting increased hydrodynamic size. These findings suggest that intraoral splint wear may cause disc damage or remodeling.

Changes in chewing pattern after surgically induced disc displacement in the rabbit temporomandibular joint

PURPOSE

This study investigated whether surgically induced disc displacement (DD) in the rabbit temporomandibular joint leads to joint dysfunction.

MATERIALS AND METHODS

Fourteen adult Japanese white rabbits were divided into two groups. Eight animals had surgically induced DD, and 6 were used as a sham operation group. Jaw movement trajectories during chewing were recorded preoperatively and 2 weeks after induction of DD. Postoperative recordings after administration of a nonsteroidal anti-inflammatory drug (NSAID) were also performed to eliminate any influence of joint pain on chewing. Vertical and horizontal ranges of chewing movement, duration of the opening and closing phase, and total cycle of chewing were analyzed. Thereafter, the presence of induced DD was confirmed histologically.

RESULTS

In the sham group, the rhythm and pattern of chewing were almost the same as preoperatively. In the experimental group, increase in the cycle duration and decrease in the vertical and horizontal ranges of movement were observed. When the sham and experimental groups were compared, there was a decreased ratio of vertical movement in the experimental animals. There was no effect of preadministration of the NSAID in either the DD or sham group. All of the experimental animals had total anterior DD histologically.

CONCLUSION

Changes in the chewing pattern of the experimental animals occurred from mechanical interference of the displaced disc. This animal model can be used as a model for human internal derangement.

Viscoelastic properties of canine temporomandibular joint disc in compressive load-relaxation

The present study was designed to investigate the mechanical properties and load-relaxation of these discs in compression. Eight discs were used for the experiments. Compression was applied to specimens up to the specified strain, and a series of load-relaxation tests was conducted on each specimen from 0.25% strain to 2.0% strain with 0.25% intervals. The load-relaxation was monitored over a period of 2 min. The elastic moduli of the canine articular discs were 30.9 and 15.8 MPa at t = 0 and 120 sec, respectively, and the discs exhibited near-linear elastic characteristics at each time within a 2-min period. At all strains, the time-dependent load-relaxation curves showed that the load decreased markedly for the initial 30 sec, after which it levelled off after 120 sec with a steady nonzero level. This relaxation feature can be well represented by Kelvin's model. It is concluded that the canine temporomandibular joint disc can be represented as a linear viscoelastic material, and that it plays an important part as a stress absorber under compression.

Discectomy of the temporomandibular joint: an experimental study in monkeys

Postoperative changes have been observed in the temporomandibular joint (TMJ) after discectomies. Animal models have often shown that interventions in the TMJ may heal uneventfully. Discectomies were performed on 14 Macaca fascicularis and macroscopic and microscopic examination performed after sacrifice of the animals. Two of the animals did not show any apparent macroscopic or microscopic changes. The remaining 12 joints showed minor to major changes. The most serious changes were seen in three joints with fibrous ankylosis and five joints showed marked destruction of the articular cartilage.

A case of the calcium pyrophosphate dihydrate (CPPD) deposition disease without condylar destruction of the temporomandibular joint

The case of calcium pyrophosphate dihydrate (CPPD) deposition disease, which occurred at a rare site in the temporomandibular joint (TMJ), is presented. A 48-year-old woman noted swelling in the preauricular area of her left cheek, which restricted her mouth opening. Radiological examination revealed a radiopaque lesion in the posterior and medial area of the left space of the TMJ. During the operation, the superior joint space was entirely filled with a solid and whitish-gray mass of chalky appearance. The lesion was partly attached to the retrodiscal tissue without any destructive change around the condyle and mandibular fossa. Histological examination revealed the foci of amorphous crystalline material to contain rhomboidal, rod and needle shaped crystals, which had cartilaginous tissue in the dense fibrous background admixed with chronic inflammatory cells and foreign body-type giant cells. The crystals were positive for von Kossa's stain and spectral peaks for phosphorus and calcium were evident by electron probe microanalysis, thus suggesting the presence of CPPD.

Effect of a surgically created disk displacement on mandibular symmetry in the growing rabbit

PURPOSE

The purpose of this study was to evaluate the contribution of unilateral disk displacement to growth changes in the young New Zealand White rabbit.

METHODS

Ten female rabbits aged 10 weeks were included in this study. The five experimental rabbits had unilateral anterior disk displacement surgery. The five controls had no surgery. The rabbits were killed at 22 weeks of age, and the mandibles hemisected and radiographed. Cephalograms were digitized and analyzed by conventional methods.

RESULTS

The gross appearance showed shortening and flattening of the articulating surface in the experimental group (P < 0.05). No significant shortening and flattening was found in the control group.

CONCLUSION

These observations suggest that surgically created internal derangement can produce altered growth in the mandible.

The behaviour of collagen fibres in stress relaxation and stress distribution in the jaw-joint disc of rabbits

The physical properties of the temporomandibular joint disc are largely attributable to its collagen fibre and proteoglycan composition and organization. Structural and stress relaxation data were obtained from the discs of six rabbits. Two stainless-steel balls, 4.8 mm dia, were used to load the disc surfaces in compression. Stress relaxation tests were performed at loads of 0.8-1.4 kg, and the disc was then placed in fixative while still in the loading apparatus in order to preserve its deformed state at equilibrium stress. After overnight fixation the discs were sectioned and assessed by means of a polarizing microscope with a rotating universal stage. This allowed measurement of three-dimensional changes in collagen fibre waviness and alignment as the result of loading. The data showed that despite significant stress relaxation and strains, only minor changes in fibre waviness and alignment occurred within the disc, reflecting its effectiveness as a tough but compliant structure, well suited to distribute load in the temporomandibular joint.

Microscopic changes in the retrodiscal tissues of painful temporomandibular joints

PURPOSE

The purpose of this study was to investigate the association between temporomandibular joint (TMJ) pain and histological changes in TMJs with disc displacement.

METHOD

Samples from capsules and posterior disc attachments from 27 TMJ pain patients who underwent surgery were compared with samples from seven asymptomatic persons.

RESULTS

On logistic regression analysis, retrodiscal tissues from the painful joints demonstrated a significantly higher density of fibroblasts, presence of narrowed and obliterated arterial lumens, and a significantly lower distribution of elastic fibers.

CONCLUSION

The results indicate that there is a difference between painful and asymptomatic joints at the microscopic level.

Age-related changes of the retrodiscal tissues in the temporomandibular joint

PURPOSE

This study compares the histologic features of the lateral capsule and lateral and central posterior disc attachment of temporomandibular joints (TMJs) in young and elderly persons.

MATERIAL AND METHODS

Samples were removed from 36 joints belonging to young persons (mean age, 30 years; age range, 16 to 39 years) and 29 joints belonging to elderly persons (mean age, 69 years; age range, 58 to 78 years). Twelve joints from elderly persons had altered disc position, whereas none of the young joints had this condition. Six-micrometer-thick sections were stained with hematoxylin-eosin and the Fränkel method (for elastic fibers). Logistic regression analysis using a likelihood-ratio test was applied for comparisons between groups and to avoid the confounding effect of differences in disc position and gender.

RESULTS

A significantly lower density of fibroblasts was observed in elderly persons in all the three areas investigated. In addition, elderly persons demonstrated a significantly lower distribution of vascular tissue and a significantly higher presence of dense connective tissue in the central third of the posterior disc attachment.

CONCLUSION

This study shows that retrodiscal tissues, which may eventually function as an articular disc during altered disc position, are susceptible to age-related connective tissue changes.