Three-dimensional theoretical model for effectively describing the effect of craniomaxillofacial structural factors on loading situation in the temporomandibular joint.

BACKGROUND: Temporomandibular joint (TMJ) overloading is considered a primary cause of temporomandibular joint disorders (TMD). Accordingly, craniomaxillofacial structural parameters affect the loading situation in the TMJ. However, no effective method exists for quantitatively measuring the loading variation in human TMJs. Clinical statistics, which draws from general rules from large amounts of clinical data, cannot entry for exploring the underlying biomechanical mechanism in craniomaxillofacial system. The finite element method (FEM) is an effective tool for analyze the stress and load on TMJs for several cases in a short period of time; however, it is difficult to generalize general patterns through calculations between different cases due to the different geometric characteristics and occlusal contacts between each case. METHODS: (1) This study included 88 subjects with 176 unilateral data to measure angle (α) of the distance to the plane of occlusion. The bone destruction score was evaluated for clinical statistics. To rule out effects of the potential factors and ensure the generality of the study, one participant with no obvious bone destruction was selected as the standard case for establishing the three-dimensional (3D) theoretical model and FEM. (2) Three groups of forces, including biting, muscles and joint reaction forces on mandible, were adopted to establish a 3D theoretical model. (3) By modifying the sagittal α and coronal three types of deviation angle (φ) of the original model, nine candidate models were obtained for the FEM studies. RESULTS: (1) The static equilibrium equations, were used to establish a 3D theoretical model for describing the loading of the TMJ. The theoretical model was validated by monotonously modifying the structural parameter in comparison to two-dimensional theoretical models reported previously; (2) The force on the TMJ gradually decreased with α, and this trend was validated by both clinic statistics and FEM results; (3) The effects of the three types of deviation angle were different. The results of the case where only rotating biting forces were considered was consistent with clinical statistics, indicating that the side with lower α experiences higher TMJ load. (4) Changing the unilateral proportionality coefficients of biting and muscle force produced opposite effects, wherein the effects of the muscle force were stronger than those of the biting forces. CONCLUSIONS: A negative correlation was observed between the joint load and α. Among the three types of asymmetric deformities, occlusal deviations were the primary factors leading to TMD. Unilateral occlusion can result in a greater load on the ipsilateral joint and should be avoided when using the side corresponding to the TMD. This study provides a theoretical basis for the biomechanical mechanism of TMD and also enables the targeted mitigation and treatment of TMD through structural modification.

The effect of bolus properties on muscle activation patterns and TMJ loading during unilateral chewing.

Mastication is a vital human function and uses an intricate coordination of muscle activation to break down food. Collection of detailed muscle activation patterns is complex and commonly only masseter and anterior temporalis muscle activation are recorded. Chewing is the orofacial task with the highest muscle forces, potentially leading to high temporomandibular joint (TMJ) loading. Increased TMJ loading is often associated with the onset and progression of temporomandibular disorders (TMD). Hence, studying TMJ mechanical stress during mastication is a central task. Current TMD self-management guidelines suggest eating small and soft pieces of food, but patient safety concerns inhibit in vivo investigations of TMJ biomechanics and currently no in silico model of muscle recruitment and TMJ biomechanics during chewing exists. For this purpose, we have developed a state-of-the-art in silico model, combining rigid body bones, finite element TMJ discs and line actuator muscles. To solve the problems regarding muscle activation measurement, we used a forward dynamics tracking approach, optimizing muscle activations driven by mandibular motion. We include a total of 256 different combinations of food bolus size, stiffness and position in our study and report kinematics, muscle activation patterns and TMJ disc von Mises stress. Computed mandibular kinematics agree well with previous measurements. The computed muscle activation pattern stayed stable over all simulations, with changes to the magnitude relative to stiffness and size of the bolus. Our biomedical simulation results agree with the clinical guidelines regarding bolus modifications as smaller and softer food boluses lead to less TMJ loading. The computed mechanical stress results help to strengthen the confidence in TMD self-management recommendations of eating soft and small pieces of food to reduce TMJ pain.

Exploring the Use of Animal Models in Craniofacial Regenerative Medicine: A Narrative Review.

The craniofacial region contains skin, bones, cartilage, the temporomandibular joint (TMJ), teeth, periodontal tissues, mucosa, salivary glands, muscles, nerves, and blood vessels. Applying tissue engineering therapeutically helps replace lost tissues after trauma or cancer. Despite recent advances, it remains essential to standardize and validate the most appropriate animal models to effectively translate preclinical data to clinical situations. Therefore, this review focused on applying various animal models in craniofacial tissue engineering and regeneration. This research was based on PubMed, Scopus, and Google Scholar data available until January 2023. This study included only English-language publications describing animal models' application in craniofacial tissue engineering (in vivo and review studies). Study selection was based on evaluating titles, abstracts, and full texts. The total number of initial studies was 6454. Following the screening process, 295 articles remained on the final list. Numerous in vivo studies have shown that small and large animal models can benefit clinical conditions by assessing the efficacy and safety of new therapeutic interventions, devices, and biomaterials in animals with similar diseases/defects to humans. Different species' anatomical, physiologic, and biological features must be considered in developing innovative, reproducible, and discriminative experimental models to select an appropriate animal model for a specific tissue defect. As a result, understanding the parallels between human and veterinary medicine can benefit both fields.

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Chewing-side preference is one of the risk factors for temporomandibular disorders (TMD), and people with chewing-side preference is more prone to have short and displaced condyles, increased articular eminence inclination and glenoid fossa depth. The proportion of TMD patients with chewing-side preference is often higher than that of the normal subjects. Clinical studies have shown a strong correlation between chewing-side preference and TMD symptoms and signs; and animal studies have shown that chewing-side preference can affect the growth, development, damage and repair of the mandible. After long-term unilateral mastication, changes in the stress within the joint cause the imbalance of temporomandibular joint (TMJ) structural reconstruction, the transformation and even destruction of the fiber structure of masticatory muscle, resulting in uncoordinated movement of bilateral muscles. The joint neurogenic diseases caused by the increase of neuropeptide substance P and calcitonin-gene-related-peptide (CGRP) released locally by TMJ may be the mechanism of TMD. This article reviews the research progress of the influence of chewing-side preference on the structure of TMJ, the relationship between chewing-side preference and TMD, and the related mechanisms.

Actualización del análisis de los movimientos mandibulares a través de articulografía electromagnética / Updating the analysis of mandibular movements through electromagnetic articulography

El objetivo de registrar los movimientos mandibulares es obtener parámetros relevantes que permitan evaluar el estado de la articulación temporomandibular (ATM) y de los músculos involucrados en la masticación. El movimiento mandibular se debe a un conjunto complejo de rotaciones y traslaciones tridimensionales realizadas por la ATM, limitado por los ligamentos y las superficies articulares de estas, y por la morfología y la alineación de los dientes, cuando la mandíbula se desplaza sobre estos límites, se llaman movimientos bordeantes mandibulares. El objetivo de este artículo es realizar una descripción actualizada de los movimientos mandibulares a través de articulografía electromagnética. Los movimientos mandibulares bordeantes se clasifican según el plano del espacio en que se muevan, de esta manera tenemos movimientos bordeantes en el plano sagital, en el plano horizontal y el plano frontal, y en cada plano dibujan un polígono distinto, llamados polígonos de Posselt. Estos polígonos pueden ser registrados mediante Articulografía electromagnética, gracias a esta tecnología también se pueden extraer algunos parámetros interesantes, como por ejemplo: la trayectoria total recorrida por la mandíbula al describir cada polígono, rangos de desplazamiento en cada plano, área total de cada polígono de Posselt. La apertura mandibular se mide como la distancia entre los márgenes incisales de los incisivos centrales superiores e inferiores en apertura máxima más la sobremordida. El análisis de esta es una parte importante del examen clínico en odontología, ya que una apertura limitada puede ser resultado de trastornos en la articulación temporomandibular, fibrosis oral submucosa, enfermedad reumática o trauma facial. Las mediciones tridimensionales que se obtienen gracias a la Articulografía electromagnética, son apropiados para determinar los rangos normales de apertura, su exactitud permite la realización de investigaciones en el área, abriendo un amplio campo en el análisis de los movimientos mandibulares.

SUMMARY: The objective of recording mandibular movements is to obtain relevant parameters that allow the evaluation of the state of the temporomandibular joint (TMJ) and of the muscles involved in mastication. Mandibular movement is due to a complex set of three-dimensional rotations and translations performed by the TMJ, limited by the ligaments and their articular surfaces, and by the morphology and alignment of the teeth, when the mandible moves over these limits, they are called mandibular border movements. The aim of this article is to provide an updated description of mandibular movements through electromagnetic articulography. Mandibular border movements are classified according to the plane of space in which they move, thus we have border movements in the sagittal plane, in the horizontal plane and the frontal plane, and in each plane they draw a different polygon, called Posselt polygons. These polygons can be recorded by electromagnetic articulography, thanks to this technology some interesting parameters can also be extracted, such as: the total trajectory covered by the mandible when describing each polygon, displacement ranges in each plane, total area of each polygon of Posselt. Mandibular opening is measured as the distance between the incisal edges of the upper and lower central incisors at maximum opening plus the overbite. The analysis of mandibular opening is an important part of the clinical examination in dentistry as a preliminary evaluation, since limited opening can be the result of temporomandibular joint disorders, submucous oral fibrosis, rheumatic disease or facial trauma. The three-dimensional measurements that are obtained thanks to the electromagnetic Articulography, are appropriate to determine the normal ranges of opening, its accuracy allows the realization of investigations in the area, opening a wide field in the analysis of mandibular movements. Analysis of mandibular opening is an important part of the clinical examination in dentistry, since limited opening can be the result of temporomandibular joint disorders, oral submucous fibrosis, rheumatic disease, or facial trauma. Analysis of mandibular opening is an important part of the clinical examination in dentistry, since limited opening can be the result of temporomandibular joint disorders, oral submucous fibrosis, rheumatic disease, or facial trauma. The three-dimensional measurements that are obtained thanks to the electromagnetic Articulography, are appropriate to determine the normal ranges of opening, its accuracy allows the realization of investigations in the area, opening a wide field in the analysis of mandibular movements.

Orthognathic surgery effects on temporomandibular joint compressive stresses.

INTRODUCTION: This study tested orthognathic surgery effects on temporomandibular joint (TMJ) compressive stresses. METHODS: Pre- (T1) and post-surgery (T2) cone-beam computed tomography images were collected from consenting subjects aged ≥15 years. Anatomical data were used to measure surgical changes in anteroposterior mandibular position and occlusal plane angle (FH-OP), estimate condylar loading areas (mm2 ) and calculate T1 and T2 TMJ and jaw muscle forces (N) during canine biting via numerical modelling. Analysis of covariance tested for sex and biting angle differences in T2 - T1 TMJ compressive stresses (TMJ force/loading area, MPa). Principal component analyses identified jaw muscle forces that accounted for changes in T2 - T1 TMJ loads. Regression analyses tested the correlations between surgical changes in mandibular position, FH-OP, TMJ loads and muscle forces. RESULTS: Of 148 cases screened, 28 females and 16 males provided complete records. Condylar loading areas were significantly smaller (P = .024) for females vs males (124 ± 5 vs 144 ± 7 mm2 ). T2 - T1 differences in TMJ compressive stresses varied by surgical change, biting angle and sex. Overall, the largest increases in TMJ compressive stresses post-surgery were for females with mandibular setbacks where FH-OP angle decreased. T2 - T1 changes in jaw muscle forces had moderate (ipsilateral, λ = 4.59; η2 = 0.071) to large (contralateral, λ = 1.49; η2 = 0.31) effects on TMJ loads. CONCLUSIONS: T2 - T1 differences in TMJ compressive stresses during canine biting were affected by surgical changes in mandibular position and occlusal plane angle, biting angle and sex. Surgical changes altered jaw muscle forces for the same biting conditions and, thus, affected TMJ loads and compressive stresses.

Numerical investigation of the biomechanical effects of orthodontic intermaxillary elastics on the temporomandibular joint.

Temporomandibular joint disorder (TMD) often coincides with malocclusion, and in some cases TMDs are reported after orthodontic treatment. Intermaxillary elastics (also known as orthodontic elastics, OE) are a common way to apply force during orthodontic treatment, and they might cause mechanical effects on the temporomandibular joint (TMJ), thereby lead to joint remodeling. It is still a controversial topic whether the adapted remodeling of the TMJ or of the alveolar bone is the main cause for the alteration of occlusion after treatment with OEs. It was the aim of this study to analyze whether variations of OEs would develop harmful effects on the healthy TMJ. A TMJ model with a masticatory system based on Hill-type muscle actuators was established. Mouth opening and closure with and without OEs were simulated, and maximum principal stresses in the disc and condylar cartilage as well as the displacement of the mandible were analyzed. We found no considerably difference in the mandibular movement without and with symmetrical OEs during mouth opening and closing. At full mouth opening, stresses in the disc and condylar cartilage of some models with OEs were much smaller than without OEs, but we did not find consistency in the results from the left and right sides of the same model (e.g. the lowest compressive stress on the left side of disc from the model with Class II OEs is much smaller than without OEs, -17.3 MPa compared with -28.2, while on the right side, there was no obvious difference). Hence, we could not conclude that OEs would develop deleterious effects on the healthy TMJ.

[Quality Evaluation of Temporomandibular Joint Images from 3 High-resolution Dynamic Sequences].

Objective To compare the image quality of three high-resolution dynamic MRI methods for evaluating the motion of temporomandibular joint disc and condyle. Methods Twenty-five patients with suspected temporomandibular joint disorders were examined by single-shot fast spin-echo (SSFSE),fast imaging employing steady-state acquisition (FIESTA),and spoiled gradient echo (SPGR) on the oblique sagittal position.Two radiologists performed subjective and objective evaluation on the images with double-blind method.The subjective evaluation included the signal intensity of mandibular condyle,articular disc,soft tissue around articular disc,and lateral pterygoid muscle,the contrast between articular disc and condyle,the contrast between articular disc and surrounding soft tissue,condylar motion,and disc movement.The objective evaluation indexes included image signal intensity,signal-to-noise ratio (SNR),and contrast-to-noise ratio (CNR).The subjective and objective indexes of the image quality were compared between the three sequences. Results The SSFSE sequence had lower signal intensity of articular disc and higher signal intensity of condyle and surrounding soft tissue than FIESTA and SPGR sequences (all P<0.001).The SPGR sequence showed higher signal intensity of lateral pterygoid muscle than the SSFSE and FIESTA sequences (P=0.017,P<0.001).Among the three sequences,SSFSE sequence showed the clearest articular disc structure (χ2=41.952,P<0.001),the strongest contrast between articular disc and condyle (χ2=35.379,P<0.001),the strongest contrast between articular disc and surrounding soft tissue (χ2=27.324,P<0.001),and the clearest movement of articular disc (χ2=44.655,P<0.001).SSFSE and FIESTA sequences showed higher proportion of disc displacement and reduction than SPGR sequence (all P<0.001).The CNR (χ2=21.400,P<0.001),SNR (χ2=34.880,P<0.001),and condyle signal intensity (F=337.151,P<0.001) demonstrated differences among SSFSE,FIESTA,and SPGR sequences.The CNR of SSFSE sequence was higher than that of FIESTA sequence (P<0.001),while it had no significant difference between SSFSE and SPGR sequences (P=0.472).In addition,the SSFSE sequence had higher SNR and signal intensity than FIESTA and SPGR sequences (all P<0.001). Conclusion The best image quality can be observed from SSFSE sequence where both the structure and movement of temporomandibular joint are well displayed.Therefore,SSFSE is preferred for the examination of temporomandibular joint movement.

Effects of bilateral sagittal split ramus osteotomy and bimaxillary osteotomies on stress distribution of temporomandibular joints in patients with maxillofacial deformity under asymmetric occlusions.

Bilateral sagittal split ramus osteotomy (BSSRO) and bimaxillary osteotomies (BSSRO plus Lefort1 osteotomy) are representative surgeries to solve maxillofacial deformity. It is important to understand the biomechanical impact of the surgeries on the temporomandibular joint (TMJ). The purpose of this study is to compare the stress variations of the patients before and after the two surgeries. Twenty-four patients with maxillofacial deformities and 14 asymptomatic subjects were recruited to be the preoperative group and control group in this study. Ten patients were performed BSSRO and other 14 underwent bimaxillary osteotomies. Finite element models of the preoperative, postoperative, and control groups were established according to the CBCT data of the subjects. The muscle forces of the left and right unilateral occlusion were applied on the models. And the contact was used to simulate the interaction within the TMJs and between the maxillary and mandibular teeth. Under the asymmetric occlusion, bimaxillary osteotomies were found to be superior to BSSRO in the stress distributions of the TMJs. The magnitude of the asymmetric stresses was strongly correlated with the TMD symptoms in the patients. And the stress variation of the postoperative TMJs was the cause of the improvement or aggravation of the TMD symptoms.

A deep dive into the static force transmission of the human masticatory system and its biomechanical effects on the temporomandibular joint.

OBJECTIVE: This study aims to investigate the biomechanical behavior and reveal the force transmission patterns of the human masticatory system through advanced three-dimensional finite element (FE) models. METHODS: The FE model was constructed according to the medical images of a healthy male adult. It contains full skull structures, detailed temporomandibular joints (TMJs) with discs, complete dentitions, masticatory muscles, and related ligaments. Several static bite scenarios were simulated to demonstrate the effects of bite positions and muscle force recruitments on the force transmission patterns. RESULTS: Molar occlusal surfaces are the primary force transmission region for clenching. Sensitivity analysis demonstrated that the stiffness of the bite substance would not alter the force transmission patterns but could affect the maximum contact stresses on the discs and the occlusal surfaces. During the unilateral clenching tasks, the high-stress region on the discal surfaces shifted ipsilaterally. The presence or absence of the molar cushions would significantly affect the biomechanical response of the masticatory system. SIGNIFICANCE: FE analysis is an effective way of investigating biomechanical responses involving complicated interactions. Enriching the static analysis of the masticatory system with a detailed model can help understand better how the forces were transmitted and the significance of TMJs during the clenching process.

Can hard and/or soft occlusal splints reduce the bite force transmitted to the teeth and temporomandibular joint discs? A finite element method analysis.

OBJECTIVE: To test whether two different materials used for occlusal splints would reduce the stress to the temporomandibular joint discs. METHODS: Geometric data from a young-adult male patient were obtained from computed tomography and magnetic resonance imaging. 3D biomodels and the finite element analyses were performed using specific software. RESULTS: The mandibular model presented the highest bone stress areas in the mandibular rami and insertion of the temporalis muscles. Regardless the material, the highest stress in the occlusal splints was located in the second molar regions on the occlusal splint surface and in the opposing mandibular second molars. Stress reduction was only observed in the internal surface of the occlusal splints embracing the maxillary teeth. No differences between occlusal splints were found in the stress intensity and distribution in either left or right TMJ discs, being concentrated more in the anterior portion of the disc. DISCUSSION: Hard acrylic OS should be preferred over soft EVA OS in the majority of cases, soft OS only for temporary use. Thinner OS (2-3 mm anterior thickness) should be preferred over thick ones (3-4 mm) in order to keep the stress concentrations in the center of the TMJ discs. Lighter contacts over heavier contacts should be preferred in the second molar OS contact surface area to prevent stress concentrations and fractures. Maxillary occlusal splints should be chosen if the teeth or implant are in the maxilla, and vice-versa.

The condylar capping for microvascular temporomandibular joint reconstruction: A preliminary study.

BACKGROUND: Defects of the temporomandibular joint (TMJ) are often difficult to be reconstructed in the correct dimensions and function. This preliminary study aims to describe a novel technique of condylar reconstruction with a microvascular flap in case of deforming arthrosis of the TMJ: condylar capping. PATIENTS AND METHODS: Four patients between 22 and 62 years old-three females and one male-with severe unilateral arthrosis of the TMJ underwent condylar capping. All patients had already had a failed conservative treatment, followed by arthroscopy with lysis and lavage and later open surgery with total or subtotal diskectomy combined with a condylar arthroplasty. Nevertheless, their pain was still at level six or more on a visual analogue scale. Moreover, they could eat only soft food. At this stage, they underwent condylar capping using an osteochondral lateral femoral condyle (LFC) flap. The surgical technique and the postoperative management are described in detail. Crucially the attachment of the lateral pterygoid muscle to the condylar neck was preserved in all cases. The patients were followed up clinically and by CT scan preoperatively, 6, and 12 months postoperatively. RESULTS: The mean height of the reconstructed neo-condyle was 6.0 mm, the mean width 16.2 mm, and the mean sagittal length 9.8 mm. The follow-up period ranged from 14 to 64 months. The procedures were uneventful for all patients, and the donor site morbidity was negligible. Twelve months later, the patients were all pain-free and able to have a regular diet. The TMJ and the knee had a normal range of movement and power. Postoperative imaging demonstrated bone healing and stable and anatomically correct condyle reconstruction. CONCLUSIONS: Based on the author's experience, the condylar capping with the LFC appears promising for reconstructing the condylar head in cases of severe osteoarthritis. Preserving the attachment of the lateral pterygoid muscle allows a complete restoration of the physiologic range of movement, including protrusion and laterotrusion of the mandible.

Research progress in effect of chewing-side preference on temporomandibular joint and its relationship with temporo-mandibular disorders / 浙江大学学报·医学版

Chewing-side preference is one of the risk factors for temporomandibular disorders (TMD), and people with chewing-side preference is more prone to have short and displaced condyles, increased articular eminence inclination and glenoid fossa depth. The proportion of TMD patients with chewing-side preference is often higher than that of the normal subjects. Clinical studies have shown a strong correlation between chewing-side preference and TMD symptoms and signs; and animal studies have shown that chewing-side preference can affect the growth, development, damage and repair of the mandible. After long-term unilateral mastication, changes in the stress within the joint cause the imbalance of temporomandibular joint (TMJ) structural reconstruction, the transformation and even destruction of the fiber structure of masticatory muscle, resulting in uncoordinated movement of bilateral muscles. The joint neurogenic diseases caused by the increase of neuropeptide substance P and calcitonin-gene-related-peptide (CGRP) released locally by TMJ may be the mechanism of TMD. This article reviews the research progress of the influence of chewing-side preference on the structure of TMJ, the relationship between chewing-side preference and TMD, and the related mechanisms.

Lateral Pterygoid Muscle Ossification After Intraoral Condylectomy.

PURPOSE: Lateral pterygoid muscle ossification has not been reported in condylectomy patients. This study aimed to explore the incidence, risk factors, and imaging characteristics of 38 cases with lateral pterygoid muscle ossification among 54 patients after condylectomy via intraoral approach. METHODS: This retrospective study included 54 patients following simultaneous orthognathic surgery and condylectomy with coronoid process resection via intraoral approach. The authors evaluated the preoperative, 1 week, 6 months, and 1 year or more postoperative computed tomographic (CT) scans for the presence of lateral pterygoid muscle ossification and its characteristics. Sex, age at the time of surgery, disease course, affected side, preoperative alkaline phosphatase, pathology diagnosis, the height of the removed condyle, condylar shape, operator, preoperative temporomandibular joint movement, and clinical symptoms were assessed as risk factors for ossification. RESULTS: No incidence of lateral pterygoid muscle ossification was found on preoperative CT images. Various small-size osseous masses were observed in the lateral pterygoid muscles on postoperative 6 months CT images in 38/54 patients (70.37%) after condylectomy. But no apparent enlargement of the osseous masses was found. No patients complained of clinical discomfort or functional disorder during the follow-up period (23.11 ± 13.16 months). No significant risk factors for ossification were found. CONCLUSIONS: Lateral pterygoid muscle ossification is relatively common in patients after condylectomy via intraoral approach. However, its enlargement is self-limited and remains stable 6 months after surgery. it has no adverse effects on the temporomandibular joint functional movement.

In vivo biomechanical effects of maximal mouth opening on the temporomandibular joints and their relationship to morphology and kinematics.

The temporomandibular joints (TMJs) are the only joints in the human skull and regulate all mandibular motions. The functions of TMJs are considerably influenced by their biomechanical surroundings. However, owing to the unique characteristics of TMJs, comprehending their kinematic and biomechanical mechanisms remains challenging. As a result, understanding how biomechanics relate to TMJ structures and motions is critical in subsequent therapies. The goal of this study is to investigate any links between morphological or kinematic factors and discal stresses during mouth opening. Our study included eight asymptomatic participants who did not show any signs or symptoms of temporomandibular disorders. The morphological parameters, kinematic properties, and stresses were determined using computed tomography (CT), magnetic resonance imaging (MRI), and subject-specific movements. Following the investigation, we discovered that the opening of the mouth was not the primary cause of TMJ stress. The stress on the discs is directly linked to condylar displacements during mouth opening. Furthermore, morphological characteristics related to the relative position of the condyles in the glenoid fossa at the intercuspal position have a limited effect on condylar displacements and stresses. In conclusion, the morphological parameters, which are commonly employed in clinics, show only static conditions in the TMJs. The kinematic parameters provide dynamic information regarding the TMJs, which can be used in the examination, diagnosis, and treatment of TMJ diseases to reduce stress.

EMG-assisted forward dynamics simulation of subject-specific mandible musculoskeletal system.

Assessment of mandibular dynamics is essential for examining stomatognathic functions, and many kinds of stomatognathic diseases, such as temporomandibular joint (TMJ) disorder and jaw tumors, require individual diagnosis and rehabilitation treatments. Musculoskeletal models of the mandible system provide an efficient tool for fulfilling these tasks, but most existing models are generic, without direct correlation to subject-specific data. For this reason, the objective of this study was to establish a subject-specific mandible modeling framework based on clinical measurements, including medical imaging, jaw kinematics, and electromyographic (EMG) acquisition. First, a non-rigid iterative closest point method was performed to register muscle insertion sites. A flexible multibody approach was introduced to describe the large deformation behavior of jaw muscles. The EMG signals of the temporalis and masseter muscles were then utilized to determine their active forces. Meanwhile, a feedback loop for tracking desired mandibular kinematics was presented to calculate the activations of jaw opening and pterygoid muscles. The subject-specific muscle forces and TMJ joint loading during jaw opening-closing movements were then calculated based on forward-inverse coupling dynamics procedure. As a validation of the proposed framework, the mandible trajectories of seven healthy subjects were predicted and compared with experimental data. The results demonstrated unintentional movement of the head-neck complex together with the activation patterns of jaw opening and lateral pterygoid muscles for different people. The proposed framework combines musculoskeletal modeling with dental biomechanical testing, providing an efficient method of predicting and understanding the dynamics of subject-specific mandible systems.

Modelo lineal vs. vectorial: estimación del movimiento mandibular y trabajo mecánico / Linear vs. vector model: estimation of mandible motion and mechanical work

Objetivo: Determinar los momentos de fuerza del haz superficial del masetero (SMH) obtenidos por modelos lineal y vectorial. Métodos: Investigación comparati-va in silico. Se obtuvo la fuerza del SMH con dinamó-metro en 12 pacientes varones adultos jóvenes para calcular el momento de la fuerza y trabajo mecánico a través de simulaciones en JAVA+ con NetBeans8.2. La descomposición de la fuerza fue F.cos α(x,y) y F.cos α(x,y,z) en el modelo lineal y vectorial respectivamen-te. Los momentos de fuerza fueron comparados por ANOVA (p<0,05). Resultados: La fuerza del SMH unila-teral obtenida con dinamómetro (2,5±0,1N) no difirió significativamente del modelo lineal (2,6±0,05N), pero difirió (p<0,001) del vectorial: 1,7, 2,2, 4,2N en x,y,z (general 2,7±0,02N). El momento medio de la fuerza en el modelo vectorial fue -17,9, -15,5, +14,3N.m-2, apuntando a la inclinación mandibular en el eje lateral en dirección caudal anterior, movimiento de inclina-ción en el eje lateral en la dirección cráneo-medial, e inclinación en el eje craneal en la dirección lateral-an-terior. El modelo lineal mostró momento de fuerza de 13,5N.m-2 apuntando un movimiento traslacional en dirección caudal-craneal en el eje anterior-posterior y menor trabajo mecánico del SMH (p=0,012). Con-clusión: Los modelos vectoriales son más eficientes proporcionando datos detallados para estimar los momentos de fuerza y el trabajo mecánico del SMH, y deben incluirse en los algoritmos de cálculo utilizados por dinamómetros (AU)

Objective: to determine the moments of force exerted by the superficial masseter head (SMH) obtained through linear models and vector ones. Methods: comparative in silico research. Data of SMH force obtained with dynamometer in 12 young adult male patients was used to calculate the moment of the force and mechanical work through simulations in JAVA+ performed with NetBeans8.2. Force decomposition was F.cos α(x,y) and F.cos α(x,y,z) in the linear and vector model respectively. The moments of force were compared by ANOVA (p<0.05). Results: Dynamometrical unilateral SMH force (2.5±0.1N) did not differ significantly from the linear model (2.6±0.05N), but differed (p<0.001) from the vector model: 1.7, 2.2, 4.2N on x,y,z (overall 2.7±0.02N). The mean moment of the force in the vector model was -17.9, -15.5, +14.3N.m-2, pointing to mandible's inclination on the lateral axis in anterior-caudal direction, inclination movement on the lateral axis in the cranio-medial direction and inclination on the cranial axis in the lateral-anterior direction. The linear model showed a moment of force of 13.5N.m-2 pointing to translational motion on caudal-cranial direction on the anterior-posterior axis and lower SMH mechanical work (p=0,012). Conclusion: Vector models are more efficient to provide detailed data to estimate the moments of force and mechanical work of SMH and should be included in the calculation algorithms used by dynamometers (AU)

Mandibular range of motion in children with juvenile idiopathic arthritis with and without clinically established temporomandibular joint involvement and in healthy children; a cross-sectional study.

BACKGROUND: Recognition of temporomandibular joint (TMJ) involvement in children with juvenile idiopathic arthritis (JIA) has gained increasing attention in the past decade. The clinical assessment of mandibular range of motion characteristics is part of the recommended variables to detect TMJ involvement in children with JIA. The aim of this study was to explore explanatory variables for mandibular range of motion outcomes in children with JIA, with and without clinically established TMJ involvement, and in healthy children. METHODS: This cross-sectional study included children with JIA and healthy children of age 6-18 years. Mandibular range of motion variables included active and passive maximum interincisal opening (AMIO and PMIO), protrusion, laterotrusion, dental midline shift in AMIO and in protrusion. Additionally, the TMJ screening protocol and palpation pain were assessed. Adjusted linear regression analyses of AMIO, PMIO, protrusion, and laterotrusion were performed to evaluate the explanatory factors. Two adjusted models were constructed: model 1 to compare children with JIA and healthy children, and model 2 to compare children with JIA with and without TMJ involvement. RESULTS: A total of 298 children with JIA and 169 healthy children were included. Length was an explanatory variable for the mandibular range of motion excursions. Each centimeter increase in length increased AMIO (0.14 mm), PMIO (0.14 mm), and protrusion (0.02 mm). Male gender increased AMIO by 1.35 mm. Having JIA negatively influenced AMIO (3.57 mm), PMIO (3.71 mm), and protrusion (1.03 mm) compared with healthy children, while the discrepancy between left and right laterotrusion raised 0.68 mm. Children with JIA and TMJ involvement had a 8.27 mm lower AMIO, 7.68 mm lower PMIO and 0.96 mm higher discrepancy in left and right laterotrusion compared to healthy children. CONCLUSION: All mandibular range of motion items were restricted in children with JIA compared with healthy children. In children with JIA and TMJ involvement, AMIO, PMIO and the discrepancy between left and right laterotrusion were impaired more severely. The limitation in protrusion and laterotrusion was hardly clinically relevant. Overall, AMIO is the mandibular range of motion variable with the highest restriction (in millimeters) in children with JIA and clinically established TMJ involvement compared to healthy children.

Temporomandibular joint and Giant Panda's (Ailuropoda melanoleuca) adaptation to bamboo diet.

Here, we present new evidence that evolutionary adaptation of the Ailuripodinae lineage to bamboo diet has taken place by morphological adaptations in the masticatory system. The giant panda in the wild and in captivity removes without an exception the outer skin of all bamboo shoots, rich in abrasive and toxic compounds, by the highly adapted premolars P3 and P4. The temporomandibular joint (TMJ) allows sidewise movement of the jaw and the premolars can, in a cusp-to-cusp position, remove the poorly digestible outer skin of the bamboo before crushing the bamboo with molars. Based on the evidence presented here, we suggest that adaptation of TMJ to lateral movement for enabling cusp-to-cusp contact of premolars is the crucial evolutionary factor as which we consider the key to understand the Ailuropodinae lineage adaptive pathway to utilize the bamboo resource.

Temporomandibular joint dysfunction following the use of a supraglottic airway device during general anaesthesia: a prospective observational study.

Supraglottic airway devices are commonly used to manage the airway during general anaesthesia. There are sporadic case reports of temporomandibular joint dysfunction and dislocation following supraglottic airway device use. We conducted a prospective observational study of adult patients undergoing elective surgery where a supraglottic airway device was used as the primary airway device. Pre-operatively, all participants were asked to complete a questionnaire involving 12 points adapted from the Temporomandibular Joint Scale and the Liverpool Oral Rehabilitation Questionnaire. Objective measurements included inter-incisor distance as well as forward and lateral jaw movements. The primary outcome was the inter-incisor distance, an accepted measure of temporomandibular joint mobility. Both the questionnaire and measurements were repeated in the postoperative period and we analysed data from 130 participants. Mean (SD) inter-incisor distance in the pre- and postoperative period was 46.5 (7.2) mm and 46.3 (7.5) mm, respectively (p = 0.521) with a difference (95%CI) of 0.2 (-0.5 to 0.9) mm. Mean (SD) forward jaw movement in the pre- and postoperative period was 3.6 (2.4) mm and 3.9 (2.4) mm, respectively (p = 0.018). Mean (SD) lateral jaw movement to the right in the pre- and postoperative period was 8.9 (4.1) mm and 9.1 (4.0) mm, respectively (p = 0.314). Mean (SD) lateral jaw movement to the left in the pre- and postoperative period was 8.8 (4.0) mm and 9.3 (3.6) mm, respectively (p = 0.008). The number of patients who reported jaw clicks or pops before opening their mouth as wide as possible was 28 (21.5%) vs. 12 (9.2%) in the pre- and postoperative period, respectively (p < 0.001) with a difference (95%CI) of 12.3% (6.7-17.9%). There was no significant difference in the responses to the other 11 questions or in the number of patients who reported pain in the temporomandibular joint area postoperatively. No clinically significant dysfunction of the temporomandibular joint following the use of supraglottic airway devices in the postoperative period was identified by either patient questionnaires or objective measurements.