Evaluation of the effect of unilateral mastication on the morphology of temporomandibular joint from the perspective of dynamic joint space.

BACKGROUND: Unbalanced alterations of temporomandibular joint morphology were associated with unilaterally masticatory habits. OBJECTIVE: This study aimed to investigate the effect of unilateral mastication on the remodelling of the temporomandibular joint using dynamic joint space. METHODS: Twelve volunteers with non-maxillofacial deformity and healthy temporomandibular joints were recruited. The 3D models of the mandible and the maxilla were reconstructed according to computed tomography. The subjects were asked to masticate French fries and peanuts unilaterally, which was recorded by a 3D motion capture system. The dynamic joint space during unilateral mastication was analysed. RESULTS: During early closure, the joint space reduction on the non-masticatory side was significantly greater than on the masticatory side (p < .05). During later closure, the joint space reduction on the non-masticatory side was significantly lower than that on the masticatory side (p < .05). The difference in joint space reduction between both sides was greater than the French fries while masticating the peanuts. CONCLUSIONS: Unilateral mastication resulted in a different major pressure area on the bilateral TMJs. Therefore, unilateral mastication might be an essential factor in the bilateral asymmetrical remodelling of the TMJ.

Evaluation of the Therapeutic Effect of Bi-Maxillary Osteotomy Using the Stress Distribution on the Temporomandibular Joint When Doing Anterior Teeth Occlusion.

The purpose of this study was to investigate how sagittal split ramus osteotomy (SSRO) and Le Fort 1 osteotomy affected the stress distribution of the temporomandibular joint (TMJ) during an anterior teeth bite using the three-dimensional (3D) finite element (FE) method. Fourteen orthognathic surgery patients were examined with mandibular prognathism, facial asymmetry, and mandibular retraction. They underwent Le Fort 1 osteotomy in conjunction with SSRO. In addition, ten asymptomatic subjects were recruited as the control group. The 3D models of the mandible, disc, and maxilla were reconstructed according to cone-beam computed tomography (CBCT). Contact was used to simulate the interaction of the disc-condyle, disc-temporal bone, and upper-lower dentition. Muscle forces and boundary conditions corresponding to the anterior occlusions were applied on the models. The stresses on the articular disc and condyle in the pre-operative group were significantly higher than normal. The contact stress and minimum principal stress in TMJ for patients with temporomandibular disorder (TMD) were abnormally higher. The peak stresses of the TMJ of the patients under anterior occlusions decreased after bimaxillary osteotomy. No postoperative TMD symptoms were found. Maxillofacial deformity led to excessive stress on the TMJ. Bimaxillary osteotomy can partially improve the stress distributions of the TMJ and relieve the symptoms of TMD.

The pressure in the temporomandibular joint in the patients with maxillofacial deformities.

BACKGROUND: Temporomandibular disorder (TMD) symptoms were found to be common in the patients with maxillofacial deformities. The mandibular structure was in relation with the stress within temporomandibular joint (TMJ). However, the current studies on the TMJ stresses in the patients with different maxillofacial deformities are not comprehensive enough. PURPOSE: The aim of this study was to investigate the compression and morphology of the TMJ in the patients with different maxillofacial deformities under central occlusion. METHODS: 24 patients and 10 asymptomatic individuals were included in this study and divided into patient groups and control group. The 3D models were reconstructed. Muscle forces and boundary conditions corresponding to the central occlusion were applied. Nine morphological parameters of mandible were evaluated. RESULTS: The minimum principal stresses in the articular disc and condyle were significantly greater than those of the control group (P<0.05). For the articular disc, the compression on the non-deviation side was greater than those on the deviation side in patients with asymmetrical mandibles. There was difference between both sides in the mandibular prognathism and retrusion groups. The joint space of patients was significantly lower than that of the control group (P<0.05). CONCLUSIONS: Maxillofacial deformities might change the condylar position within the articular fossa, which decreased the joint space and increased the compression within TMJ. The patients with asymmetry mandible suffered greater pressure within TMJ on the non-deviation side. The bilaterally over-developed and under-developed mandible in patients might also increase the compression within TMJ.

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.

The effect of mandibular movement on temporomandibular joint morphology while eating French fries.

BACKGROUND: The preferred masticatory side was reported to be almost always the same as the affected side of the temporomandibular disorder. Unbalanced alterations of temporomandibular joint morphology were found to be associated with unilaterally masticatory habits. The aim of this study was to investigate the effect of the mandibular movement on the remodeling of temporomandibular joint during eating French fries using a 3D motion capture system. METHODS: Twelve volunteers with non-maxillofacial deformity and a healthy temporomandibular joint were recruited. The 3D models of the mandible and the maxilla were reconstructed according to computed tomography. The subjects were asked to eat French fries by unilaterally mastication, which was recorded by a 3D motion capture system. The trajectories of the incisors and the condyles and the condylar acceleration during unilateral mastication were analyzed. RESULTS: During incisal biting, there was no significant difference in the condylar trajectories between the left and right sides (P > 0.05). During unilateral mastication, the average displacement and acceleration of the masticatory condyles were significantly lower than those of the non-masticatory condyles (P < 0.05). The trajectory angles of the masticatory condyles were significantly steeper than those of the non-masticatory condyle (P < 0.05). During swallowing, there was no obvious movement of the mandible. CONCLUSIONS: Between both temporomandibular joints, unilateral mastication resulted in significant differences in the regions of the condylar movement within the articular fossa, and then caused different compressive regions of the temporomandibular joints. Thus, unilateral mastication might result in a significantly different pattern of temporomandibular joint remodeling between the two sides.

Temporomandibular condylar articulation and finite helical axis determination using a motion tracking system.

Kinematics play an important role in assessing the recovery of the patients' temporomandibular joint (TMJ) and occlusal functions. The finite helical axis (FHA), which simplifies three parameters in Euler-angle descriptions, provides a comprehensive insight into TMJ kinematics. Additionally, the FHA is one of the potential indicators used in the diagnosis and treatment of TMDs and the design and use of the TMJ replacement. This study aimed to illustrate the changes in the FHA of the TMJs during basic mandibular motions. Visible markers were rigidly affixed to the mandibular dentition and a helmet. Four active motions were registered: mouth opening, mandibular protrusion, and left and right lateral protrusions. According to the models reconstructed from the computed tomography of the same subject and the relative distance of the markers, subject-specific condylar tracking was achieved, and the FHAs for the four motions were determined. In addition to the irregular distribution in the initial opening, the FHA of the opening formed an "L-shaped" curve. Mandibular protrusion is a translational motion with little rotation. Additionally, the FHA crossed the ipsilateral TMJ during lateral protrusions, from initially vertical directions generally to horizontal directions at the front view. The proposed method provides a feasible way for measuring the FHA.

Mathematical analysis of the condylar trajectories in asymptomatic subjects during mandibular motions.

The understandings of motional regular and dynamic information during the mandibular motions are essential to investigate the dysfunctions of temporomandibular joints (TMJ). This study aims to develop a method to record the mandibular movements and analyze the condylar trajectory, velocity, and acceleration in asymptomatic individuals during mandibular motions. Thirteen asymptomatic subjects were strictly selected without symptoms of temporomandibular disorders (TMDs). An optical tracking system was chosen for recording mandibular motions. Curve fitting was used for fitting the trajectories of condyles, notches and lower incisor, and the articular eminence outlines. The sagittal plane (YoZ) provided a better view for condylar trajectories during mouth opening and mandibular protrusion, whereas the coronal plane (XoZ) offered a superior view during lateral protrusions. A parabola had good performance in fitting the trajectories of the condyle, incisor, and outlines with a superior goodness of fit (r2) during mouth opening and mandibular protrusion; linear functions were suitable for fitting the trajectories of the contralateral condyle during lateral protrusions. The velocity during the opening process was lower than that during the closing process, and so were the accelerations. The sagittal space between the articular eminences and condyles during mouth opening and mandibular protrusion were close, 2.8 and 2.7 mm, respectively. The sagittal space, velocity, and acceleration can provide dynamic information of TMJs. Three-dimensional motion analyses of temporomandibular joints during the mandibular motions were conducted to exact the mathematic information of temporomandibular joints. From curve fitting process, the fluctuation can be eliminated and the dynamic information can be obtained. And the parabola was better for the condylar trajectories in the sagittal plane of opening and mandibular protrusion. As to the lateral protrusions, the linear function is suitable for the condylar trajectories in coronal plane. The condylar curve of asymptomatic subjects can set as a reference to diagnose and treat for the patients with associated dysfunctions.

Biomechanical analysis of temporomandibular joints during mandibular protrusion and retraction motions: A 3d finite element simulation.

BACKGROUND AND OBJECTIVE: Temporomandibular disorders (TMDs) represent a wide range of musculoskeletal disorders associated with the maxillofacial system, which negatively affect the daily activities of patients. TMD symptoms are caused by the temporomandibular joint (TMJ) overloading. TMJ motions are frequent and can trigger overloading and imbalanced loads on the TMJs, which are assumed to be dangerous. The condyles move forward a lot during mandibular protrusion, which is possibly harmful to the biomechanical environment of the TMJs. The aim of this study was to investigate the biomechanical behavior of TMJs during mandibular protrusion and retraction. METHODS: Six three-dimensional maxillofacial system models from asymptomatic subjects were established through computed tomography (CT) and magnetic resonance imaging (MRI). The mandibular protrusion and retraction were recorded using an optical tracking system. Finite element analysis was used to simulate the biomechanical behaviors of the TMJs during the movements. RESULTS: The simulation results were validated to be effective by comparison with the MRIs. The results indicated that the stresses during the protrusion and retraction were approximately equal at the same condylar displacement. Meanwhile the discal stresses, relatively correlated with the condylar displacement, increased as the condylar displacement increased during the protrusion and decreased as the condylar displacement decreased in the retraction. In addition, the average peak maximum and minimum principal stresses of the discs were 0.186 and -0.192 MPa, respectively. CONCLUSIONS: The models were reasonable for the investigation of the TMJs motion. Based on the results, three quadratic polynomials were proposed to describe the relationship between the stresses and the condylar displacements. In clinical diagnosis, the functions are helpful in the prediction of the discal stresses by measuring the condylar displacement.

Three-dimensional finite element analysis of temporomandibular joints in patients with jaw deformity during unilateral molar clenching before and after orthognathic surgery.

ABSTRACT: To analyze the effects of orthognathic surgery on stress distributions in the temporomandibular joint (TMJ) of patients with jaw deformity during unilateral molar clenching (UMC) by using three-dimensional (3D) finite element method.Nine patients with jaw deformity (preoperative group, 26.1 ±â€Š5.6 years old) and 9 asymptomatic subjects (control group, 22.0 ±â€Š6.0 years old) were selected. Furthermore, the patients with jaw deformity were also considered as the postoperative group after undergoing orthognathic surgery. Finite element models for the mandible, articular disc, and maxilla were developed through cone beam computed tomography. Contact was used to simulate the interaction of the articular disc, condyle, fossa, and upper and lower dentition. The muscle forces and boundary conditions corresponding to the UMC were applied on the models.The stresses on both TMJs of the control group were significantly different, whereas there was no significant difference on both sides for the preoperative group. All the stresses of the preoperative group were greater than those of the control and postoperative groups, except the minimum principal stress on the ipsilateral fossa.Orthognathic surgery is beneficial for alleviating the abnormal stress distributions on TMJ.

Biomechanical study on the changes of stress in temporomandibular joints after the orthognathic surgery in patients with mandibular prognathism: a 3D finite element study.

PURPOSE: This study aimed to analyze the changes of the stress distributions in TMJs for the pre- and postoperative patients with mandibular prognathism under unilateral occlusions, a frequent occlusion in mastication. METHODS: Pre- and six-mouth postoperative cone-beam computed tomography images of thirteen patients diagnosed with mandibular prognathism were scanned and used to construct complete maxillofacial models, assigned as the Pre and Post group, respectively. Another ten asymptomatic individuals were defined as the Control group. The inhomogeneous properties were assigned to the models. The muscle forces and boundary conditions corresponding to left and right unilateral occlusions were applied on the models. The analysis of variation (ANOVA) was chosen for the comparison among the groups. RESULTS: The results showed that the Pre group had abnormal stress distributions ang higher stress level in TMJs, compared with those of the Post and Control groups. Moreover, from clinical cases, symptoms of temporomandibular disorders (TMDs) always followed with increased stresses. CONCLUSION: Generally, orthognathic surgeries could improve the stress distribution in TMJs of the patients with mandibular prognathism under the unilateral occlusions. However, the postoperative complications, especially symptoms of TMD, were closely related to changes of stress for patients with mandibular prognathism after orthognathic surgeries. Individual virtual surgery and finite element analysis should be conducted to prevent complications in TMJ.

Biomechanical responses of temporomandibular joints during the lateral protrusions: A 3D finite element study.

BACKGROUND & OBJECTIVE: This study aims to analyze the stress distributions in temporomandibular joints (TMJs) during the left and right protrusions and explore the mechanical reasons for these stress distributions. METHODS: Computed tomography and magnet resonance images of 5 asymptomatic subjects were used to reconstruct the bone and soft tissue of the maxillofacial models with a pair of detailed TMJs. An optical motion-track system captured the left and right protrusions of the subjects. Inhomogeneous material properties were assigned to the models according to the gray value of the images. Then, the captured data were inputted as the loadings of the finite element models. Different from previous studies, a more relaxed position was used as the initial position of the jaw, which could better mimic the internal loads with lower initial stress. RESULTS: The stresses on the discs for all the subjects during the motions were under the fracture stress. The stress distributions exhibited an obvious asymmetry. Among them, three subjects had a contralateral-greater stress distribution during both left and right lateral protrusions. The greater stresses always lay in the left disc for one subject, and another subject had an ipsilateral-greater stress distribution during the motions. Besides, the stress distributions in a single disc were various due to the different nature of movements. CONCLUSION: Excessive stretch and squeeze, which was originated from great and little condylar displacements towards fossa during the motions, had a negative influence on the stresses in discs. Thus, the detections about the condylar displacement, even biomechanical analysis, were necessary to provide dynamically biomechanical information in the treatment of TMJ associated dysfunctions.

Biomechanical behaviour of temporomandibular joints during opening and closing of the mouth: A 3D finite element analysis.

Temporomandibular joints (TMJs) constitute a pair of joints that connect the jawbone to the skull. TMJs are bilateral joints which work as one unit in conducting daily functions such as speaking, mastication, and other activities associated with the movement of the jaw. Issues associated with the TMJs may arise due to various factors-one such factor being the internal load on the TMJ. These issues may contribute to temporomandibular disorders (TMD). This study aims to evaluate the mandibular trajectories and the associated stress changes during the process of opening the mouth on the TMJs of an asymptomatic subject. The mouth opening motion was recorded by a motion capturing system using models of the mandible and maxilla constructed based on the computed tomography (CT). Two discs constructed based on magnetic resonance imaging (MRI). Finite element analysis was performed on the relative motion of the mandible to the maxilla and validated. The process modelled by these displacements provided less than 10% error in terms of deformation. The simulation results indicate that the lateral intermediate zone-the head and neck of the mandible-and the articular eminence sustained the most significant stresses during the mouth opening motion. The results also suggested that the stresses increase as the range of opening increases with the greatest von Mises stress, tensile, and compressive stress found at the position of maximal opening.