Biomechanical and biochemical outcomes of porcine temporomandibular joint disc deformation

3D model construction and biomechanical analysis of temporomandibular joint disc perforation based on arthrography

OBJECTIVES

Disc perforation (DP) is a severe type of temporomandibular joint (TMJ) disorder. Arthrography-assisted CBCT can visually detect the location and size of DPs. This study aims to use imaging modeling software to construct a three-dimensional (3D) visual model of DP, simulating its biomechanical impact on the TMJ to provide a scientific basis for diagnosis and treatment.

MATERIALS AND METHODS

TMJ imaging data were obtained through arthrography and CBCT scans. Imaging modeling software was used to reconstruct and measure the DICOM files in 3D. The model was imported into biomechanical analysis software to simulate the static occlusal state of the mandibular muscles on the TMJ. The effects of DP on the mechanical properties of the TMJ were assessed via von Mises stress and total deformation analysis.

RESULTS

(1) The maximum von Mises stress (MVMS) on the affected side of the disc was significantly greater than that on the unaffected side. This stress was negatively correlated with the height of the condylar head and positively correlated with the perforation volume. (2) The maximum total deformation (MTD) of the affected side's disc was significantly greater and negatively correlated with the condylar head height. (3) The MVMS of the condyle was markedly greater on the affected side than on the unaffected side.

CONCLUSION

(1) DPs may increase stress on bilateral TMJs, with the affected side experiencing significantly greater stress. (2) A larger perforation volume can result in greater stress on the affected side's disc. (3) The height of the affected condylar head can have an adverse effect on the stress and deformation of bilateral TMJs.

CLINICAL RELEVANCE

TMJ arthrography can assist clinicians in accurately determining the location, morphology, and size of the disc perforation, enabling early diagnosis and intervention to prevent further enlargement. Additionally, the restoration and protection of the condylar head height contribute to maintaining the stability of the intra-articular stresses within the TMJ.

Temporomandibular joint disc responses to installation and removal of the experimental malocclusion

BACKGROUND

Aberrant occlusion and aging are two main risks for temporomandibular joint (TMJ) degeneration.

OBJECTIVE

To assess the combined impact of occlusion and age on TMJ disc.

METHODS

To avoid the confounding impact of gender, presently, 126 female C57BL/6J mice, 63 youngsters, 6-week old and 63 adults, 28-week old, were used. An experimental bilateral anterior crossbite (BAC) relation was created by installing metal tubes onto the mandibular incisors. Mice were sacrificed at 3, 7 and 11 weeks (n = 9). Additionally, the installed tubes were removed at 7 weeks in removal groups and the TMJs were sampled after another 4 weeks (n = 9). Disc changes were detected by histomorphology, immunohistochemistry, and western blot assays.

RESULTS

Disc deformation was obvious in BAC groups. The typical change was hyperplasia at the posterior region of the disc where there was significant infiltration of inflammatory cells. Expressions of the inflammatory markers, including tumour necrosis factor-α and interleukin-1β, and the catabolic markers, including fibronectin (FN), FN N-terminal fragments, and vascular endothelial growth factor-A, were all increased. The changes were more obvious in adults than in youngsters. Removal of BAC attenuated inflammatory and catabolic changes in the youngsters, but the inflammatory markers recovered little in the adults.

CONCLUSION

TMJ disc responds to BAC by degeneration and inflammation, and respond to BAC removal by rehabilitation. Adult discs show severer degeneration responses to BAC and a lower level of anti-inflammatory capability to BAC removal than the youngster's discs. Animals cannot be equated with humans. The human disc response to occlusion changes worth further exploration.

The mechanics of tissue-engineered temporomandibular joint discs: Current status and prospects for enhancement

The temporomandibular joint (TMJ) disc is an essential protective but vulnerable fibrocartilage. Their high mechanical strength is vital in absorbing loads, reducing friction, and protecting the condylar surface. Many diseases can lead to the destruction or degeneration of the mechanical function of the TMJ disc. Unfortunately, conservative treatment is ineffective in restoring the defective mechanical properties of the discs. Tissue engineering has been investigated as a promising alternative treatment approach to approximate the properties of native tissue. However, it is difficult for tissue-engineered discs to obtain sufficient mechanical properties. Several approaches have been proposed to improve the mechanical properties of tissue-engineered constructs. In this review, we summarized the mechanical properties of native TMJ discs and discussed the current mechanical testing methods. We then summarized the current advances in improving the mechanical properties of TMJ disc tissue-engineered constructs. Moreover, existing challenges and outbreak directions are discussed. This review assists future research in better understanding the mechanical properties of both native and tissue-engineered TMJ discs. It provides new insights into future mechanical property enhancement for TMJ disc tissue engineering.

The relationship between the articular disc in magnetic resonance imaging and the condyle in cone beam computed tomography: A retrospective study

BACKGROUND

The authors retrospectively studied the relationship between the morphology and position of the articular disc in magnetic resonance imaging (MRI) and the morphology and position of the condyle in cone beam computed tomography (CBCT), with the purpose for providing reference for clinical diagnosis and treatment of temporomandibular disorders (TMD).

METHODS

Patients with both CBCT and MRI imaging data were studied retrospectively, excluding TMJ tumour, fracture, severe condylar morphological abnormalities, non-intercuspal position, and poor quality images. A total of 744 temporomandibular joints (TMJs) from 372 patients were included, with the mean age of 25.94±11.04Y (75 males and 297 females). T2-weighted image (T2WI) of MRI imagings were used to evaluate disc morphology and disc displacement, while CBCT was obtained to evaluate the condylar bone and sagittal condylar position. Data were analysed by Pearson Chi square test and Spearman correlation coefficient.

RESULTS

THE DISTRIBUTION OF 744 TMJS IS AS FOLLOWS: 1) DISC MORPHOLOGY: contracture (37.1 %) > biconcave (32.9 %) > irregular (18.5 %) > lengthened (11.4 %); 2) disc position: ADDWoR (48.3 %) > NA (26.9 %) > ADDWR (21.6 %) > PDDWR (2.8 %) > PDDWoR (0.4 %); 3) condylar position: concentric (43.7 %) > posterior (37.6 %) > anterior (18.7 %); 4) condylar bone: normal (63.4 %)> abnormal (36.6 %). There were significant differences in the distribution of disc morphology and disc position between the sex (P < 0.05). There were significant differences in the distribution of disc position and condylar morphology amongst the age groups (P < 0.05). There were significant differences in the distribution of disc position, condylar position and condylar morphology amongst disc morphology (P < 0.05), and there were positive correlation between disc position(r = 0.703, P = 0.000), the score of condyle (r = 0.478, P = 0.000) and disc morphology respectively. There were significant differences in the distribution of disc position and condylar position amongst condylar morphology (P < 0.05). There was a positive correlation between disc position and condyle morphology (r = 0.413, P = 0.000), and a negative correlation between condyle position and condyle morphology (r=-0.152, P = 0.000). There were significant differences in the distribution of disc position amongst condylar position (P < 0.05), but there was no linear correlation (P = 0.159).

CONCLUSIONS

The mutual distribution of disc morphology, disc position, condylar morphology and condylar position was statistically significant. Disc displacement did not necessarily lead to condylar bone changes, but 92.7 % TMJs with condylar bone abnormalities had disc displacement.

TRIAL REGISTRATION

This study was retrospectively registered on 28/03/2022 and endorsed by the Ethics committee (LCYJ2022014).

Microstructural, Micromechanical Atlas of the Temporomandibular Joint Disc

The temporomandibular joint (TMJ) disc is mainly composed of collagen, with its arrangement responding to efficient stress distribution. However, microstructural and micromechanical transformations of the TMJ disc under resting, functional, and pathological conditions remain unclear. To address this, our study presents a high-resolution microstructural and mechanical atlas of the porcine TMJ disc. First, the naive microstructure and mechanical properties were investigated in porcine TMJ discs (resting and functional conditions). Subsequently, the perforation and tear models (pathological conditions) were compared. Following this, a rabbit model of anterior disc displacement (abnormal stress) was studied. Results show diverse microstructures and mechanical properties at the nanometer to micrometer scale. In the functional state, gradual unfolding of the crimping cycle in secondary and tertiary structures leads to D-cycle prolongation in the primary structure, causing tissue failure. Pathological conditions lead to stress concentration near the injury site due to collagen interfibrillar traffic patterns, resulting in earlier damage manifestation. Additionally, the abnormal stress model shows collagen damage initiating at the primary structure and extending to the superstructure over time. These findings highlight collagen's various roles in different pathophysiological states. Our study offers valuable insights into TMJ disc function and dysfunction, aiding the development of diagnostic and therapeutic strategies for TMJ disorders, as well as providing guidance for the design of structural biomimetic materials.

Relationships between functional temporomandibular joint space and disc morphology, position, and condylar osseous condition in patients with temporomandibular disorder

OBJECTIVE

To investigate the correlations between joint space and temporomandibular joint (TMJ) components and the compressive states of the disc and condyle subsequent to joint space changes.

MATERIALS AND METHODS

A total of 240 TMJs were categorized according to disc morphology, disc position, and condylar osseous condition. The two-dimensional (2D) and three-dimensional (3D) measurements were compared. The functional joint space (FJS) and disc areas on closed- and open-mouth images (DA-C and DA-O) were also calculated, and the joint space was measured in five directions. Different groups of TMJ components were compared. A spring model was used to simulate the effect of condylar displacement on the disc and condyle.

RESULTS

Disc morphology was strongly correlated with its position. The measurements were equivalent between 2D and 3D methods. DA-C and FJS differed significantly between groups. The DA-C to FJS ratio differed between the Class 2 and Class 3 groups and between disc displacement groups with and without reduction. Altered disc morphology and position were correlated with significant changes in joint space in the 60°, 90°, and 120° directions. Despite minor discrepancies among condylar osseous conditions, reduced joint space was correlated with bone destruction at the corresponding site. The spring model stimulation revealed that condylar displacement caused elevated stresses on the disc and condyle.

CONCLUSIONS

Condylar displacement causes joint space alterations while exerting compressive pressure on both the disc and condyle.

CLINICAL RELEVANCE

Proper condylar positioning within the fossa is recommended to ensure sufficient articular disc accommodation.

In vitro differentiation of human induced pluripotent stem cells into temporomandibular joint disc like cells

Temporomandibular joint discs (TMJ discs) are unable to repair themselves in disease states, while induced stem cell differentiation is a common method to repair tissue defects. Nowadays, kinds of stem cells are attempted for tissue regeneration of TMJ disc, but these methods have several downsides, which limit their wide application. The proliferation and differentiation ability of human induced pluripotent stem cells (hiPSC) provides a new research direction for TMJ disc tissue regeneration. In this study, we investigated the feasibility of induced differentiation of hiPSC into TMJ disc cells in vitro and the differentiation efficiency of different methods to clarify the possibility and conditions of hiPSC application in TMJ disc tissue engineering. We collected sheep TMJ disc cells cultures for adding in hiPSC culture environment and treated hiPSC by both direct induction and Transwell co-culture for 7 days, 14 days and 21 days. The secretion of extracellular matrix in TMJ disc cells was detected by Sirius Red and Safranin O staining. Collagen Ⅰ and Collagen Ⅱ were qualitatively detected by immunohistochemical staining. The expression of extracellular matrix genes (type I collagen (COL1A1), type II collagen(COL2), glycosaminoglycan (GAG)), chondrogenic differentiation gene SOX9 and pluripotency gene OCT4 were detected by RT-qPCR. Our results showed that hiPSC had the ability to differentiate to TMJ disc cells by direct induction in TMJ disc cell culture medium and by Transwell co-culture method. The highest degree of differentiation was observed after 14 days of direct induction, while Transwell co-culture showed significant differentiation at different times and with different major directions. Meanwhile, Transwell co-culture not only differentiates hiPSC but also promotes the growth and proliferation of TMJ disc cells. Our study is valuable to investigate the possibility of differentiation of hiPSC toward TMJ disc cells and to determine the time of differentiation. It provides new ideas for the selection of seed cells for TMJ disc tissue engineering.

Synthetic materials in craniofacial regenerative medicine: A comprehensive overview

The state-of-the-art approach to regenerating different tissues and organs is tissue engineering which includes the three parts of stem cells (SCs), scaffolds, and growth factors. Cellular behaviors such as propagation, differentiation, and assembling the extracellular matrix (ECM) are influenced by the cell's microenvironment. Imitating the cell's natural environment, such as scaffolds, is vital to create appropriate tissue. Craniofacial tissue engineering refers to regenerating tissues found in the brain and the face parts such as bone, muscle, and artery. More biocompatible and biodegradable scaffolds are more commensurate with tissue remodeling and more appropriate for cell culture, signaling, and adhesion. Synthetic materials play significant roles and have become more prevalent in medical applications. They have also been used in different forms for producing a microenvironment as ECM for cells. Synthetic scaffolds may be comprised of polymers, bioceramics, or hybrids of natural/synthetic materials. Synthetic scaffolds have produced ECM-like materials that can properly mimic and regulate the tissue microenvironment's physical, mechanical, chemical, and biological properties, manage adherence of biomolecules and adjust the material's degradability. The present review article is focused on synthetic materials used in craniofacial tissue engineering in recent decades.

Is Arthroscopic Disk Repositioning Equally Efficacious to Open Disk Repositioning? A Systematic Review

PURPOSE

Temporomandibular joint disc repositioning surgery is 1 of the treatment modalities used for treating anterior disc displacement of the temporomandibular joint. The procedure can be arthroscopic disc repositioning or open disc repositioning. This systematic review measured and compared the efficacy of arthroscopic and open disc repositioning procedures.

MATERIALS AND METHODS

The authors conducted a systematic review without meta-analysis by performing a literature search electronically and manually covering arthroscopic and open disc repositioning studies published up to July 2020 in Pubmed, Embase, and Cochrane databases. Surgical outcomes such as changes in maximal incisal opening (MIO) and pain scores, temporomandibular joint noises, diet consistency, malocclusion, and postoperative complications were extracted and analyzed.

RESULTS

A total of 28 studies were included in the review and split into those assessing open disc repositioning (n = 13) and those assessing arthroscopic disc repositioning (n = 15). The average age of the study patients in the included studies was 31.5 ± 6.8 years, and women represented 83.3% of the study population. Both arthroscopic and open disc repositioning showed to be efficacious in reducing pain and increasing MIO. Due to heterogeneity in study designs and data reporting between the studies, no quantitative analysis was performed, and the groups were not directly compared.

CONCLUSIONS

Both arthroscopic and open disc repositioning led to significant improvements in clinical outcomes based on pain scores and MIO. This study highlights the need for comparative studies of the 2 techniques with well-documented case selection including standardized diagnosis based on Wilkes stages and rigorous outcomes assessment including patient reported outcomes.

Roles of functional strain and capsule compression on mandibular cyst expansion and cortication

OBJECTIVE

Cyst expansion in bone involves bone resorption but is often accompanied by adjacent bone formation with cortication. The mechanisms for these two apparently opposite processes remain unclear. From a mechanobiological perspective, functional strain drives bone remodeling, which involves both bone apposition and resorption. In this study, we explore the role of functional strain in cyst growth.

DESIGN

Using a three-dimensional finite element analysis model of a simulated cyst at the of right first mandibular molar mesial apex, we examined three loading conditions, representing biting on the right molar, left molar and incisors, respectively. Comparison was made with an identical finite element model without the simulated cyst.

RESULTS

Under all loading conditions, finite element analysis revealed higher strain energy density within the bone lining the cyst compared with the non-cyst model, which is consistent with bone formation and cortication observed clinically. Further analysis demonstrated overall compression of the simulated cyst capsule under all loading conditions.We interpret compression of the capsule as indicating resorption of the adjacent bone surface.

CONCLUSIONS

We conclude that functional stress results in dominant compression of the soft tissue capsules of bony cysts, contributing to cyst expansion. Also, functional strain becomes elevated in the bone immediately adjacent to the soft tissue cyst capsule, which may drive bone formation and cortication.

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.

The Temporomandibular Joint of the Domestic Dog (Canis lupus familiaris) in Health and Disease

This study aimed to characterize the histological, biomechanical and biochemical properties of the temporomandibular joint (TMJ) of the domestic dog in health and disease. In addition, we sought to identify structure-function relationships and to characterize TMJ degenerative lesions that may be found naturally in this species. TMJs (n = 20) from fresh cadaver heads (n = 10) of domestic dogs were examined macroscopically and microscopically and by cone-beam computed tomography. The TMJ discs were evaluated for their mechanical and biochemical properties. If TMJ arthritic changes were found, pathological characteristics were described and compared with healthy joints. Five (50%) dogs demonstrated macroscopically normal fibrocartilaginous articular surfaces and fibrous discs and five (50%) dogs exhibited degenerative changes that were observed either in the articular surfaces or the discs. In the articulating surfaces, these changes included erosions, conformational changes and osteophytes. In the discs, degenerative changes were represented by full-thickness perforations. Histologically, pathological specimens demonstrated fibrillations with or without erosions, subchondral bone defects and subchondral bone sclerosis. Significant anisotropy in the TMJ discs was evident on histology and tensile mechanical testing. Specifically, the discs were significantly stiffer and stronger in the rostrocaudal direction compared with the mediolateral direction. No significant differences were detected in compressive properties of different disc regions. Biochemical analyses showed high collagen content and low glycosaminoglycan (GAG) content. No significant differences in biochemical composition, apart from GAG, were detected among the disc regions. GAG concentration was significantly higher in the central region as compared with the caudal (posterior) region. The TMJ of the domestic dog exhibits similarities, but also differences, compared with other mammals with regards to structure-function relationships. The TMJ articular surfaces and the disc exhibit degenerative changes as seen in other species, including perforation of the disc as seen in man. The degenerative changes had greater effects on the mechanical properties compared with the biochemical properties of the TMJ components. Translational motion of the TMJ does occur in dogs, but is limited.

Properties of the Temporomandibular Joint in Growing Pigs

A subset of temporomandibular joint (TMJ) disorders are attributed to joint degeneration. The pig has been considered the preferred in-vivo model for the evaluation of potential therapies for TMJ disorders, and practical considerations such as cost and husbandry issues have favored the use of young, skeletally immature animals. However, the effect of growth on the biochemical and biomechanical properties of the TMJ disc and articulating cartilage has not been examined. The present study investigates the effect of age on the biochemical and biomechanical properties of healthy porcine TMJs at 3, 6, and 9 months of age. DNA , hyrdroxyproline, and glycosaminoglycan (GAG) content were determined and the discs and condyles were tested in uniaxial unconfined stress relaxation compression from 10% - 30% strain. TMJ discs were further assessed with a tensile test to failure technique, which included the ability to test multiple samples from the same region of an individual disc to minimize the intra-specimen variation. No differences in biochemical properties for the disc or compressive properties at 30% stress relaxation in the disc and condylar cartilage were found. In tension, no differences were observed for peak stress and tensile modulus. The collagen content of the condyle were higher at 9 months than 3 months (p<0.05), and the GAG content was higher at 9 months than 6 months (p<0.05). There was a trend of increased compressive instantaneous modulus with age. As such, age matched controls for growing pigs are probably appropriate for most parameters measured.

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.

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.