Discal attachments of the human temporomandibular joint

Morphologic and histologic characterization of sheep and porcine TMJ as large animal models for tissue engineering applications

Objective

The aim of this study was to compare and characterize the structural and ultrastructural organization of the temporomandibular joint (TMJ) between two large animal models for use in the development of tissue engineering strategies.

Materials and methods

Whole TMJs from sheep and pigs were evaluated with micro-computed tomography (μCT) for morphology and quantitative analyses of bone parameters. Histological examination was performed on the TMJ disc and its attachments to investigate regional distribution of collagen, elastin, and glycosaminoglycans (GAGs).

Results

μCT analyses demonstrate higher bone mineral density (BMD) in the temporal fossa compared to the mandibular condyle in both species, with this variable being significantly higher in sheep than pig. Quantitative morphometry of the trabecular condyle reveals no statistical differences between the species. Histology demonstrates similar structural organization of collagen and elastin between species. Elastin staining was nearly twofold greater in sheep than in the pig disc. Finally, Safranin-O staining for GAGs in the TMJ disc was localized to the intermediate zone in the sheep but was absent from the porcine disc.

Conclusions

Our findings show some important differences in the pig and sheep TMJ μCT variables and histology and composition of the disc and discal attachment. These disparities likely reflect differences in masticatory and TMJ functional loading patterns between the two species and provide insights into large animal models towards human applications.

Clinical relevance

As with the established pig model, the sheep is a suitable large animal model for TMJ research such as regenerative strategies, with specific considerations for design parameters appropriate for human-analog applications.

Evaluation of Auditory Changes in Patients Undergoing Temporomandibular Joint Discectomy

PURPOSE

Discectomy is 1 of the preferred TMJ surgical procedure for the treatment of internal derangements when conservative and minimally invasive treatments have failed. The purpose of the current study is to investigate whether a TMJ discectomy operation influences auditory function and clinical variables.

MATERIALS AND METHODS

This prospective study was composed of patients who underwent a TMJ discectomy operation between 2016 and 2020. Auditory function was evaluated with pure tone audiometry, tympanometry, and acoustic reflex tests at preoperatively (T₀), postoperative first week (T₁), first month (T₂), and third month (T₃). Clinical parameters including maximum mouth opening (MMO) and TMJ pain were also evaluated at T₀, T₁, T₂, T₃, and sixth month (T₄).

RESULTS

The study consisted of 17 patients (5 males, 12 females) with a mean age of 42.65. A significant reduction in VAS pain scores and MMO values compared to baseline values was achieved in all follow up periods (P^T0-T1= .001; P^T0-T2/T3/T4 < .001). In pure tone audiometry, a significant increase in T₁-T₀ comparisons at 1000 Hz, 2000 Hz, 6000 Hz, 8000 Hz frequencies, and pure tone average (P = .008; P = .005; P = .012; P = .002; P = .001) was observed. In T₃-T₀ comparisons, a statistically significant decrease was observed in pure tone thresholds at 125 Hz and 8000 Hz frequencies (P = .008; P = .01). There was no statistically significant difference in middle ear pressure and compliance values at T₁, T₂, and T₃ compared to T₀ (P ˃ .05). Type C tympanogram was seen in 3 patients at T₁ and in 1 patient at T₂. Acoustic reflex tests were positive in all patients.

CONCLUSIONS

Although mild changes occurred in auditory tests in the early postoperative period, TMJ discectomy procedure has no permanent effect on auditory function.

A magnetic resonance imaging study on the temporomandibular joint disc-condyle relationship in young asymptomatic adults

The aim of this study was to assess the temporomandibular joint (TMJ) disc-condyle relationship in asymptomatic young adults. Ninety-three volunteers aged 19-23 years without temporomandibular disorder (TMD) symptoms underwent TMJ magnetic resonance imaging (MRI). The condylar centre and apex methods were used to measure and analyse the position of the disc in the oblique sagittal plane, and the reliability of the two methods was compared by calculating the intra-class correlation coefficient (ICC). Furthermore, 18 of the volunteers were randomly selected for three-dimensional (3D) reconstruction of the TMJ structure and the disc-condyle relationship. The 3D TMJ structure was established by semi-automatic segmentation of the condyle and articular disc in ITK-SNAP software; the condylar apex method was then performed. It was found that only 33.3% of the posterior edge of the articular discs were located in the normal 12 o'clock position with respect to the condyle. Moreover, this study suggests that the condylar centre method lacks accuracy when compared to the condylar apex method in regard to the measurement of the TMJ disc-condyle relationship (0 < ICC_cen < ICC_apex < 1). The position of the articular disc (left and right) was more forward in young women when compared to young men. However, there was no significant difference in the TMJ disc-condyle position between the left and right sides in the same individual, although the two joint discs in the same individual were not completely symmetrical.

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.

Histological and Immunofluorescence Study of Discal Ligaments in Human Temporomandibular Joint

The temporomandibular joint (TMJ) is a bilateral synovial articulation stabilized by several anatomical structures such as ligaments. The existence of articular capsule reinforcement structures have been described in the lateral and medial sides of disc which have been defined as collateral ligaments, lateral and medial. Despite that, some macroscopic observations support that these collateral ligaments do not belong to the articular capsule but they belong to the disc. By that, the aim of the present work was to evaluate morphological aspects of TMJ from cadaveric frozen heads by histological and immunofluorescence techniques in order to verify the origin and insertion of lateral and medial collateral ligaments. Results show that both lateral and medial ligaments origin from the disc and insert directly to the articular cartilage of mandibula condyle. These data open a new approach in the study of human TMJ.

Approaches to improve integration and regeneration of an ex vivo derived temporomandibular joint disc scaffold with variable matrix composition

Due to their natural biochemical and biomechanical characteristics, using ex vivo tissues as platforms for guided tissue regeneration has become widely accepted, however subsequent attachment and integration of these constructs in vivo is often overlooked. A decellularized porcine temporomandibular joint (TMJ) disc has shown promise as a scaffold to guide disc regeneration and preliminary work has shown the efficacy of surfactant (SDS) treatment within the fibrocartilaginous disc to remove cellular components. The majority of studies focus on the intermediate region of the disc (or disc proper). Using this approach, inherent attachment tissues can be maintained to improve construct stability and integration within the joint. Unlike human disc attachment tissue, the porcine attachment tissues have high lipid content which would require a different processing approach to remove immunogenic components. In order to examine the effect of delipidation on the attachment tissue properties, SDS and two organic solvent mixtures (acetone/ethanol and chloroform/methanol) were compared. Lipid and cellular solubilization, ECM alteration, and seeded human mesenchymal stem cell (MSC) morphology and viability were assessed. Quantitative analysis showed SDS treatments did not effectively delipidate the attachment tissues and cytotoxicity was noted toward MSC in these regions. Acetone/ethanol removed cellular material but not all lipids, while chloroform/methanol removed all visible lipid deposits but residual porcine cells were observed in histological sections. When a combination of approaches was used, no residual lipid or cytotoxicity was noted. Preparing a whole TMJ graft with a combined approach has the potential to improve disc integration within the native joint environment.

Potential Role of Rebamipide in Osteoclast Differentiation and Mandibular Condylar Cartilage Homeostasis

Background:

Temporomandibular joint osteoarthritis (TMJ-OA) is a degenerative disease that involves changes in subchondral bone and progressive degradation of cartilage. Currently, rebamipide, a gastroprotective drug, is administered to protect gastric mucosa and accelerate ulcer healing.

Objectives:

Recent studies have shown that rebamipide also attenuates cartilage degeneration by suppressing oxidative damage and inducing homeostasis of the extracellular matrix of articular chondrocytes. Regarding the latter, reduced expression of cathepsin K, NFATc1, c-Src, and integrin β3, and increased expression of nuclear factor-kappa B, have been found to be mediated by the transcription factor, receptor activator of nuclear factor kappa-B ligand (RANKL).

Methods:

Treatment with rebamipide was also found to activate, mitogen-activated protein kinases such as p38, ERK, and JNK to reduce osteoclast differentiation. Taken together, these results strongly indicate that rebamipide mediates inhibitory effects on cartilage degradation and osteoclastogenesis in TMJ-OA.

Results and Conclusion:

Here, we highlight recent evidence regarding the potential for rebamipide to affect osteoclast differentiation and TMJ-OA pathogenesis. We also discuss the potential role of rebamipide to serve as a new strategy for the treatment of TMJ-OA.

Structure-Function Relationships of Temporomandibular Retrodiscal Tissue

It is estimated that 2% to 4% of the US population will seek treatment for temporomandibular joint (TMJ) symptoms, typically occurring with anterior disc displacement. The temporomandibular retrodiscal tissue (RDT) has been postulated to restrict pathologic disc displacement. To elucidate RDT function, understanding regional RDT biomechanics and ultrastructure is required. No prior biomechanical analysis has determined regional variations in RDT properties or associated biomechanical outcomes with regional variations in collagen and elastin organization. The purpose of this study was to determine direction- and region-dependent tensile biomechanical characteristics and regional fibrillar arrangement of porcine RDT. Incremental stress relaxation experiments were performed on 20 porcine RDT specimens, with strain increments from 5% to 50%, a ramp-strain rate of 2% per second, and relaxation periods of 2.5 min. Tensile characteristics were determined between temporal and condylar regions and anteroposterior and mediolateral directions. RDT preparations were imaged using second-harmonic generation (SHG) microscopy for both collagen and elastin. Young's modulus showed significant differences by region ( P < 0.001) and strain ( P < 0.001). Young's modulus was <1 MPa from 5% to 20% strain, before increasing from 20% to 50% strain to a maximum of 2.9 MPa. Young's modulus trended higher in the temporal region and mediolateral direction. Instantaneous and relaxed moduli showed no significant difference by region or direction. Collagen arrangement was most organized near the disc boundary, with disorganization increasing posteriorly. Elastin was present at the disc boundary and RDT mid-body. Porcine RDT demonstrated region- and strain-dependent variations in tensile moduli, associated with regional differences in collagen and elastin. The small tensile moduli suggest that the RDT is not resistive to pathologic disc displacement. Further biomechanical analysis of the RDT is required to fully define RDT functional roles. Understanding regional variations in tissue stiffness and ultrastructure for TMJ components is critical to understanding joint function and for the long-term goal of improving TMJ disorder treatment strategies.

Recent Tissue Engineering Advances for the Treatment of Temporomandibular Joint Disorders

Temporomandibular disorders (TMDs) are among the most common maxillofacial complaints and a major cause of orofacial pain. Although current treatments provide short- and long-term relief, alternative tissue engineering solutions are in great demand. Particularly, the development of strategies, providing long-term resolution of TMD to help patients regain normal function, is a high priority. An absolute prerequisite of tissue engineering is to understand normal structure and function. The current knowledge of anatomical, mechanical, and biochemical characteristics of the temporomandibular joint (TMJ) and associated tissues will be discussed, followed by a brief description of current TMD treatments. The main focus is on recent tissue engineering developments for regenerating TMJ tissue components, with or without a scaffold. The expectation for effectively managing TMD is that tissue engineering will produce biomimetic TMJ tissues that recapitulate the normal structure and function of the TMJ.

Biomechanical analysis of fractures in the mandibular neck (collum mandibulae)

After treatment of fractures in the neck of the mandible by means of immobilization of the dentition, often more or less severe manifestations of malocclusion remain. It was hypothesized that this is caused by an altered articulation in the jaw joint on the affected side. Furthermore, it was hypothesized that an anteriorly displaced condyle, as observed frequently as a side effect of the treatment, is caused by pull of the lateral pterygoid muscle, despite maxillomandibular fixation. Intervention experiments were performed in silico to test these hypotheses. With a biomechanical model of the human masticatory system alterations were applied mimicking a fractured mandibular neck and configurations that had been observed after healing. It was predicted that the altered articulation in the jaw joint caused asymmetrical jaw movements despite symmetrical muscle activation. The jaw was predicted to close with an open bite similar to clinical observations. The predicted laterodeviations, however, were not in accordance with clinical observations. Despite maxillo-mandibular fixation the lateral pterygoid muscle was able to pull the mandibular condyle out of its fossa in anterior direction. Consequently, despite some methodological limitations, in general the predictions corroborated the hypotheses.

Variations of the attachment of the superior head of human lateral pterygoid muscle

INTRODUCTION

The superior head of the lateral pterygoid muscle (LPM), is closely related to the temporomandibular joint (TMJ) and plays a role in the aetiology of temporomandibular disorders. Increased activity of this muscle has been implicated in the anterior displacement of the TMJ disc. However, there is uncertainty about the manner of the LPM attachment to the disc-condyle complex.

AIM

The aim of this study was to investigate the exact anatomy of the attachment of the superior head of the LPM (SLPM) to the disc-condyle complex of the TMJ.

MATERIAL AND METHODS

Thirty-six TMJs were examined - both sides of 18 Greek cadavers (eight males and 10 females, mean age 79.6 years). Examination of the attachment of the SLPM was undertaken viewed under the dissecting microscope.

RESULTS

Variation in the attachment of the SLPM was categorized into three types: in type I, the SLPM inserted into the condyle and the disc-capsule complex (55.5%). In type II, the SLPM only inserted into the condyle (27.8%). In type III, the SLPM inserted purely into the disc-capsule complex (16.7%).

CONCLUSIONS

This study demonstrates that there are three different attachment types of the SLPM to the disc-condyle complex. The type III variation could be involved in the TMJ pathology. The knowledge of the variations of the SLPM attachment could be useful for precise surgical and pharmaceutical approaches.

Role of intra-articular ozone gas injection in the management of internal derangement of the temporomandibular joint

OBJECTIVES

This study was carried out to compare intra-articular ozone gas injection and drug therapy as conservative treatment modalities for internal derangement of the temporomandibular joint (TMJ).

STUDY DESIGN

Sixty patients (49 female and 11 male) with bilateral internal derangement of the TMJs, disc displacement with reduction, were included in this study. They were divided randomly into 2 equal groups. The first group was treated by a direct injection of ozone gas into the superior joint space. Each joint received 2 mL ozone-oxygen mixture (ozone gas concentration 10 μg/mL). The injections were repeated 2 times per week for 3 weeks. The second group received nonsteroidal antiinflammatory drugs and muscles relaxants. The clinical signs and symptoms before and after the treatment were assessed according to Helkimo's clinical dysfunction index.

RESULTS

The results showed that 87% of the patients who received ozone gas injections into the superior joint space (n = 26) either completely recovered (37%; n = 11) or improved (50%; n = 15). In the second group, 33% of the patients who were treated with nonsteroidal antiinflammatory drugs and muscle relaxants (n = 10) showed only an improvement in their clinical dysfunction indexes.

CONCLUSIONS

Based on the findings of the present study, we can consider that intra-articular ozone gas injection is a promising new treatment modality for internal derangement of the TMJ. However, further clinical and experimental studies are required to provide direct evidence for its mechanism of action and to substantiate our results.

Histological study of the extratympanic portion of the discomallear ligament in adult humans: a functional hypothesis

This study was carried out on histological aspects of the extratympanic portion of the discomallear ligament (DL) in adult humans. The temporomandibular joint (TMJ) was dissected bilaterally in 20 cadavers; in 15 cases the articular disc (AD) and the retroarticular tissue were extirpated. The extratympanic portion of the DL had the shape of a base-down triangle, in relation to the AD, and an upper vertex, in relation to the petrotympanic fissure. In five cases, the base, measured bilaterally, had an average length of 6.4 mm, while the distance from the base to the upper vertex averaged 9.3 mm in length. The extratypanic portion of the DL is an intrinsic ligament of the TMJ, composed of collagen fibres and abundant elastic fibres. We propose that this ligament could act as a tensor of the synovial membrane in movements of the TMJ.

The attachments of the temporomandibular joint disc: a biochemical and histological investigation

OBJECTIVE

The complex movement of the temporomandibular joint (TMJ) disc during mastication is controlled in large part by the disc's attachments to the surrounding tissues. This study seeks to address the lack of available quantitative data characterizing the extracellular matrix composition of the discal attachments and how these properties compare to the disc.

DESIGN

Porcine TMJ disc-attachment complexes were carefully dissected into six discal attachments and five TMJ disc regions. All samples were assayed biochemically for total collagen, glycosaminoglycan (GAG), DNA, and hydration. Additionally, histology was performed on the whole joint to investigate the anatomy of the disc-attachment complex, and to verify the regional distribution of matrix components.

RESULTS

Quantitative biochemical assays showed that overall water content was fairly constant in all disc and attachment regions. Disc regions generally showed higher sulfated GAG and collagen content than the attachments. In contrast, the attachments contained greater DNA content than the disc. Histological staining supported the quantitative results and also indicated more elastic fibres to be present in the attachments than the disc.

CONCLUSIONS

Although macroscopically the TMJ disc and its attachments form a seamless complex within the joint, a closer look at regional biochemical constituents reveals that these two components are distinct. Whilst the disc and attachments both contain the same major constituents, the relative amounts of these components vary based on the functional requirements of the tissue. These results can further understanding of both TMJ biology and pathology.

Pathologic changes of the lateral pterygoid muscle in patients with derangement of the temporomandibular joint disk: objective measures at MR imaging

BACKGROUND AND PURPOSE

The superior head of the lateral pterygoid muscle (SHLP), which inserts on the anterior disk of the temporomandibular joint (TMJ), can spasm, contracting and exerting forward traction on the disk. This mechanism can lead to anterior displacement. In TMJ dysfunction, it is hypothesized that the SHLP will demonstrate morphologic changes with measurable changes in signal intensity related to atrophy or muscular edema, or both. The goal of this study was to evaluate the lateral pterygoid muscle (LPM) in patients with TMJ dysfunction.

MATERIALS AND METHODS

Patients with displacement of the TMJ disk with and without reduction were identified through a review of radiology reports. Absolute measurements of thickness as well as region-of-interest measurements were placed over the 2 heads of the LPM bilaterally on sagittal T1- and T2-weighted images. Statistically significant differences between the superior and inferior heads of the LPM were calculated with use of a 1-tailed Student t test and were correlated with the degree of disk derangement.

RESULTS

In patients with disk derangement, significantly increased region-of-interest values on T2- and T1-weighted images were demonstrated within the SHLP. No patients with anatomically normal disks demonstrated a statistically significant difference in region-of-interest values between the superior and inferior heads of the LPMs.

CONCLUSION

Correlation between increased region-of-interest values and pathologic alteration of the relationship between the condylar head and disk was identified. In patients with displacement of the anterior disk with and without reduction, region-of-interest values were significantly increased, which indicates abnormal signal intensity involving the superior head of the LPM.

Effect of Hyperactivity of the Lateral Pterygoid Muscle on the Temporomandibular Joint Disk

In this study, the effect of hyperactivity of the lateral pterygoid muscle (LPM) on the temporomandibular joint (TMJ) disk during prolonged clenching was examined with a mathematical model. Finite element models of the TMJ were constructed based on magnetic resonance images from two subjects with or without internal derangement of the TMJ. For each model, muscle forces were used as a loading condition for stress analysis for 10 min clenching. Furthermore, an intermittent increase of the LPM force with intervals of 1 min was applied. In the asymptomatic model, large stresses were found in the central and lateral part of the disk at the onset of clenching. In the retrodiscal tissue, stress relaxation occurred during the first 2 min of clenching. When the force of the LPM increased temporarily, the disk moved anteriorly and returned to its original position afterward. In the symptomatic model, large stresses were observed in both the posterior region of the disk and the retrodiscal tissue throughout clenching. Upon temporary increase of the LPM force, the disk was elongated anteriorly, which appeared to be irreversible. These results indicate that hyperactivity of the LPM may be involved in the progression of disk displacement.

Organization and function of the collagen fiber system in the human temporomandibular joint disk and its attachments

The collagen fiber organization in the anterior band (AB), intermediate zone (IZ) and posterior band (PB) of the disk of the human jaw joint disk and in its attachments was studied under the polarizing microscope. Observations were made on serially sectioned joints (n = 6) and three sets of disk samples sectioned along mutually perpendicular planes (n = 21). The collagen fiber bundles in all disk regions branch and join or are decussated with other bundles. The fibers of the IZ were oriented generally parallel to the disk surfaces. Most of these fibers extend into the AB and PB where they either join with transverse or vertically oriented fiber groups or pass through the bands into the disk attachments. The lateral branching/decussation angles of fibers in the IZ and adjacent regions of the AB and PB were measured in the central region of four disks. The mean angle for all regions was 28 +/- 13 degrees . The mean angles in the region transitional between the IZ and AB and in the anterior region of the IZ were significantly greater than those in the posterior part of the IZ (p = 0.001 and 0.050 for the two comparisons). The large caliber, vertically oriented fibers in the AB, IZ and PB were counted in nine specimens. Disk dimensions were also measured in these specimens. The vertically and transversely oriented bundles were more frequent in the band regions. The number of vertically oriented fiber bundles varied within and between the disk bands. Vertical fiber number in the AB was greater laterally than medially (p = 0.04). In the PB the fiber number was greater than in either the AB or IZ (p = 0.000 for both comparisons) and within the PB itself the fiber number was greater in its thicker, medial half (p = 0.014). The fiber number in the AB and IZ was not different. The thickness of the AB, IZ and PB and disk length was measured in sections located laterally, centrally and medially. No difference in disk length was found across these planes. Statistically significant differences were found in regional disk thickness. In all of the mediolateral planes, the AB and PB were thicker than the IZ and the PB was thicker than the AB (p = 0.000 for all comparisons). The IZ was thicker medially than laterally (p = 0.034). The PB was thicker centrally and medially than laterally (p = 0.002 and 0.001, respectively). PB thickness in its central and medial regions was not different. The findings, combined with other evidence, suggest that the fiber system of the disk serves a stress distribution function and that within the AB and PB, the regions containing the greatest number of vertical fibers may also be the sites of greatest compressive stress during jaw function.