Growth orientations, rather than heterogeneous growth rates, dominate jaw joint morphogenesis in the larval zebrafish

In early limb embryogenesis, synovial joints acquire specific shapes which determine joint motion and function. The process by which the opposing cartilaginous joint surfaces are moulded into reciprocal and interlocking shapes, called joint morphogenesis, is one of the least understood aspect of joint formation and the cell-level dynamics underlying it are yet to be unravelled. In this research, we quantified key cellular dynamics involved in growth and morphogenesis of the zebrafish jaw joint and synthesised them in a predictive computational simulation of joint development. Cells in larval zebrafish jaw joints labelled with cartilage markers were tracked over a forty-eight hour time window using confocal imaging. Changes in distance and angle between adjacent cell centroids resulting from cell rearrangement, volume expansion and extracellular matrix (ECM) deposition were measured and used to calculate the rate and direction of local tissue deformations. We observed spatially and temporally heterogeneous growth patterns with marked anisotropy over the developmental period assessed. There was notably elevated growth at the level of the retroarticular process of the Meckel's cartilage, a feature known to undergo pronounced shape changes during zebrafish development. Analysis of cell dynamics indicated a dominant role for cell volume expansion in growth, with minor influences from ECM volume increases and cell intercalation. Cell proliferation in the joint was minimal over the timeframe of interest. Synthesising the dynamic cell data into a finite element model of jaw joint development resulted in accurate shape predictions. Our biofidelic computational simulation demonstrated that zebrafish jaw joint growth can be reasonably approximated based on cell positional information over time, where cell positional information derives mainly from cell orientation and cell volume expansion. By modifying the input parameters of the simulation, we were able to assess the relative contributions of heterogeneous growth rates and of growth orientation. The use of uniform rather than heterogeneous growth rates only minorly impacted the shape predictions whereas isotropic growth fields resulted in altered shape predictions. The simulation results suggest that growth anisotropy is the dominant influence on joint growth and morphogenesis. This study addresses the gap of the cellular processes underlying joint morphogenesis, with implications for understanding the aetiology of developmental joint disorders such as developmental dysplasia of the hip and arthrogryposis.

Orofacial Pain Symptoms Among Chinese Older Adults in the Last Year of Life

The aims of this study were to examine the prevalence of orofacial pain symptoms and its associated factors in Chinese older adults in the last year of life. We retrospectively followed 1,646 participants (60 years or older) in the last year of life to death from the Chinese Longitudinal Healthy Longevity Survey (CLHLS). The 6-month prevalence of toothache and jaw joint pain or facial pain for older adults in the last year of life to death were 14.1% and 4.5%, respectively. Older adults who had lower socioeconomic status, were smokers, and had any chronic disease tended to have orofacial pain symptoms. This study generated interesting but counterintutive findings that Chinese older adults who brusehed their teeth at least daily and those who had at least one natural teeth were more likely to have orofacial pain. It is important to include dental care as a part of end-of-life medical treatment.

An evolutionarily conserved cis-regulatory element of Nkx3.2 contributes to early jaw joint morphology in zebrafish

The acquisition of movable jaws was a major event during vertebrate evolution. The role of NK3 homeobox 2 (Nkx3.2) transcription factor in patterning the primary jaw joint of gnathostomes (jawed vertebrates) is well known, however knowledge about its regulatory mechanism is lacking. In this study, we report a proximal enhancer element of Nkx3.2 that is deeply conserved in gnathostomes but undetectable in the jawless hagfish. This enhancer is active in the developing jaw joint region of the zebrafish Danio rerio, and was thus designated as jaw joint regulatory sequence 1 (JRS1). We further show that JRS1 enhancer sequences from a range of gnathostome species, including a chondrichthyan and mammals, have the same activity in the jaw joint as the native zebrafish enhancer, indicating a high degree of functional conservation despite the divergence of cartilaginous and bony fish lineages or the transition of the primary jaw joint into the middle ear of mammals. Finally, we show that deletion of JRS1 from the zebrafish genome using CRISPR/Cas9 leads to a transient jaw joint deformation and partial fusion. Emergence of this Nkx3.2 enhancer in early gnathostomes may have contributed to the origin and shaping of the articulating surfaces of vertebrate jaws.

REHABILITATION OF MASTICATION AND LACK OF SPACE TREATMENT IN NARROW EDENTULOUS WITH FIXED-FIXED BRIDGE

Background: Loss of posterior teeth can lead to disharmony in the curvature of the jaw. Antagonistic teeth and surrounding teeth will migrate to the edentulous causing reduced mastication function and TMJ disturbance. Several cases of narrow edentulous occurred due to tooth shifting caused by edentulous that was left empty for a long period. Creating a fixed-fixed bridge is aimed to restore the aesthetics, function, and comfort for patients which caused by the missing teeth. Fixed-fixed bridge consist of a retainer that function as a support to the abutment; a pontic that function to replace the missing tooth; and a connector that function to connect the pontic and the retainer. A narrow space for pontics can disrupt the aesthetic and functional aspects. Case Report: A 24 year-old male patient was referred to Prosthodontic Clinic, Gusti Hasan Aman Dental Hospital with a complain of pain on the jaw joint and missing of left lower molar for about 5 years. Patient always masticate on one side after the left lower molar was missing. Extraoral examination found the patient to be in good condition, no enlargement of major salivary glands, the vital signs were good, but upon TMJ examination there was clicking sounds on the left side. Intraoral examination showed space narrowing resulted from mesial and distal drifting of 37 and 35 but not significant, therefore it was still possible to perform rehabilitation using fixed-fixed bridge with abutments on 37 and 35 with modification of pontic shape for 36 to resemble a premolar tooth with occlusal surface resembling a molar tooth. Treatment planning for fixed prosthetic using fixed-fixed bridge with porcelain fused to metal material on 35, 36, and 37 with ridge lap pontic type modification Conclusions: Treatment was successful to provide enough space for the pontic by modification of the shape and the size of the pontic. Keywords: Fixed-fixed bridge. lack of space, mastication.

The broad role of Nkx3.2 in the development of the zebrafish axial skeleton

The transcription factor Nkx3.2 (Bapx1) is an important chondrocyte maturation inhibitor. Previous Nkx3.2 knockdown and overexpression studies in non-mammalian gnathostomes have focused on its role in primary jaw joint development, while the function of this gene in broader skeletal development is not fully described. We generated a mutant allele of nkx3.2 in zebrafish with CRISPR/Cas9 and applied a range of techniques to characterize skeletal phenotypes at developmental stages from larva to adult, revealing loss of the jaw joint, fusions in bones of the occiput, morphological changes in the Weberian apparatus, and the loss or deformation of bony elements derived from basiventral cartilages of the vertebrae. Axial phenotypes are reminiscent of Nkx3.2 knockout in mammals, suggesting that the function of this gene in axial skeletal development is ancestral to osteichthyans. Our results highlight the broad role of nkx3.2 in zebrafish skeletal development and its context-specific functions in different skeletal elements.

Radiation Diagnostics in Treatment of Displacement of a Joint Disk of a Temp-Jaw Joint and Myofascial Disorders

Purpose: Determination of the volume and sequence of radiation studies in the treatment of patients with displacement of the articular disc of the temporomandibular joint (TMJ)and myofascial pain disorders. Material and methods: The study included 48 patients with displacement of the articular disc of the TMJ and myofascial pain disorders. Clinical criteria for articular displacement were confirmed by MRI and CBCT. Studies of the function of the masticatory muscles were carried out at the Synapsis electromyograph. All patients underwent complex treatment, including relaxation of the masticatory muscles and relief of pain using injections of botulinum toxin in the actual masticatory, temporal and lateral pterygoid muscles (LPM), followed by repositioning split therapy. For the introduction of muscle relaxant in LPM, we have developed and applied external periarticular injection access to LPM. The method is based on reaching the zone of joint attachment of the upper and lower heads of the LPM with MRI navigation. Surveillance continued for up to 12 months with MRI monitoring of the position of the articular disc. Results: The stages of treatment of SJS of the TMJ with control use of MRI and CT, as well as a method for the administration of botulinum toxin under MRI navigation, have been developed. The first stage included CT and MRI of the temporomandibular joint, the second stage – injections of botulinum toxin into the masticatory muscles using the developed periarticular access to the LPM with MRI navigation, as well as CBCT with a splint to control the new (established) position of the lower jaw; the third and fourth stages included continuation of the reduction splint therapy, correction of the splint, observation for 3-6 months with control CBCT after 6 months to assess the position of the mandible without splint. Achieved an increase in the posterior and upper temporomandibular joint distances and the correct position of the lower jaw. Conclusion: Performing radiation studies on time at certain stages of treatment, differing in their content and volume, provided a complete diagnosis, planning treatment measures and monitoring the results.

A Finite Element Modeling and Simulation of Human Temporomandibular Joint with and Without TM Disorders: An Indian Experience

Temporomandibular joint (TMJ) is anatomically the most intricate joint which connects the lower jaw to the upper jaw and regulates jaw movements. It significantly deals with mastication and speech. It is hence imperative to study the mechanics and functioning of the jaw joint to devise alternative solutions for its replacement whenever required. Further, human skulls are anthropologically categorized into three types – African, Asian and European. Out of these, the Indian skull is also a bit different than its Asian counterparts because of its osteology and skeletal biology. Hence, a comprehensive biomechanical and computational study is essential to provide customized solutions. For the present study, four different loading conditions are selected to perform finite element analysis on the human skull, Anonymized and unidentifiable CT scan data sets from open-source web platforms are converted to STL and then 3D models using 3D slicer. Finite element analysis of jaw joint is carried out. Results based on Von Mises stress studies show significant behavioral differences under varying load conditions. Hence, it is crucial to identify solutions for TMJ disorders of the Indian population.

In-Ear Energy Harvesting: Source Characterization and Mechanical Simulator (Part I)

During daily activities, such as chewing, eating, speaking, and so forth, the human jaw moves, and the earcanal is deformed by its anatomic neighbor called the temporomandibular joint (TMJ). Given the frequency of those jaw joint activities, the earcanal dynamic movement is a promising source of energy in close proximity to the ear, and such energy can be harvested by using a mechanical–electrical transducer dubbed energy harvester. However, the optimal design of such micromachine requires the characterization of the TMJ’s range of motion, its mechanical action on the earcanal, and its mechanical power capability. For that purpose, this research presents two methods for analyzing the earcanal dynamic movements: first, an in situ approach based on the measurement of the pressure variation in a water-filled earplug fitted inside the ear canal, and second, an anatomic-driven mechanism in the form of a chewing test fixture capable of reproducing the TMJ kinematics with great precision. The pressure earplug system provides the earcanal global dynamics, which can be derived as an equivalent displaced volume, while the chewing test fixture provides the discrete displacement along the earcanal wall. Both approaches are complementary and contribute to a better analysis of the interaction between the TMJ and earcanal. Ultimately, knowledge of the maximum displacement area and the derived generated power within the earcanal will lead to the design of a micromachine, allowing for the further investigation of in-ear energy harvesting strategies.

Knockdown of hspg2 is associated with abnormal mandibular joint formation and neural crest cell dysfunction in zebrafish

Background Heparan sulfate proteoglycan 2 (HSPG2) encodes for perlecan, a large proteoglycan that plays an important role in cartilage formation, cell adhesion, and basement membrane stability. Mutations in HSPG2 have been associated with Schwartz-Jampel Syndrome (SJS) and Dyssegmental Dysplasia Silverman-Handmaker Type (DDSH), two disorders characterized by skeletal abnormalities. These data indicate a function for HSPG2 in cartilage development/maintenance. However, the mechanisms in which HSPG2 regulates cartilage development are not completely understood. Here, we explored the relationship between this gene and craniofacial development through morpholino-mediated knockdown of hspg2 using zebrafish. Results Knockdown of hspg2 resulted in abnormal development of the mandibular jaw joint at 5 days post fertilization (DPF). We surmised that defects in mandible development were a consequence of neural crest cell (NCC) dysfunction, as these multipotent progenitors produce the cartilage of the head. Early NCC development was normal in morphant animals as measured by distal-less homeobox 2a (dlx2a) and SRY-box transcription factor 10 (sox10) expression at 1 DPF. However, subsequent analysis at later stages of development (4 DPF) revealed a decrease in the number of Sox10 + and Collagen, type II, alpha 1a (Col2a1a)+ cells within the mandibular jaw joint region of morphants relative to random control injected embryos. Concurrently, morphants showed a decreased expression of nkx3.2, a marker of jaw joint formation, at 4 DPF. Conclusions Collectively, these data suggest a complex role for hspg2 in jaw joint formation and late stage NCC differentiation.

The role of Gdf5 in the development of the zebrafish fin endoskeleton

BackgroundThe development of the vertebrate limb skeleton requires a complex interaction of multiple factors to facilitate correct shaping and positioning of bones and joints. Growth and differentiation factor 5 (Gdf5), a member of the transforming growth factor-beta family (TGF-β) is involved in patterning appendicular skeletal elements including joints. Expression of gdf5 in zebrafish has been detected within the first pharyngeal arch jaw joint, fin mesenchyme condensations and segmentation zones in median fins, however little is known about the functional role of Gdf5 outside of Amniota.ResultsWe generated CRISPR/Cas9 knockout of gdf5 in zebrafish and analysed the resulting phenotype at different developmental stages. Homozygous gdf5 mutant zebrafish displayed changes in segmentation of the endoskeletal disc and, in consequence, loss of posterior radials in the pectoral fins. Mutant fish also displayed affected organisation and length of skeletal elements in the median fins, however joint formation and mineralisation process seemed unaffected.ConclusionsOur study demonstrates the importance of Gdf5 for the paired and median fin endoskeleton development in zebrafish and reveals that the severity of the effect increases from anterior to posterior side of the elements. Our findings are consistent with phenotypes observed in human and mouse appendicular skeleton in response to Gdf5 knockout, suggesting a broadly conserved role for Gdf5 in Osteichthyes.