Biomechanical effects of mandibular deviation on the temporomandibular joint in patients with mandibular prognathism under incisal occlusion.

PURPOSE: The aim of this study was to investigate the biomechanical effects of mandibular deviation on the TMJ in patients with mandibular prognathism before and after orthognathic surgery using three-dimensional finite element analysis. METHODS: Eight patients with mandibular prognathism without deviation, eight patients with mandibular prognathism with deviation and sixteen normal subjects were recruited. Three-dimensional models of the maxillofacial were reconstructed using MIMICS. Nine muscle forces were used to simulate incisal occlusion and contact was used to simulate fossa-disc-condyle interactions. RESULTS: Before surgery, the stress in the TMJ was generally greater in the Pre-MD&MP group than in the Pre-MD group; it was much greater in both groups than in the control group, ranging from about 2 to 12 times as great in the Pre-MD group and from about 5 to 64 times as great in the Pre-MD&MP group. After orthognathic surgeries, the stresses in the Post-MP&MD were significantly reduced by approximately 21.7 % to 93.4 %. And in the Post-MP group, the stresses were reduced by approximately 1.4 % to 51.1 %. CONCLUSION: Mandibular deviation exacerbated the abnormal stress distribution in the TMJ of patients with mandibular prognathism. Orthognathic surgeries could improve the stress distribution in patients with mandibular prognathism (with and without deviation). TMD was closely related to the stress levels of the TMJ.

Morphologic characteristics of temporomandibular joint on the patients with anterior disc displacement without osteoarthritis: a case-based research.

We investigated the effect of anterior disc displacement without osteoarthritis (ADDwoOA) on the morphology of the temporomandibular joint (TMJ) utilizing three-dimensional (3D) models of 23 asymptomatic individuals and 30 ADDwoOA patients. Statistical analyses between the groups were performed by measuring 10 morphological parameters. ADDwoOA patients showed significantly decreased levels of the sagittal ramus angle (SRA) and joint spaces compared with asymptomatic subjects. Moreover, the patients who had recovered exhibited normal joint spaces levels. Consequently, ADDwoOA caused the condyles to move backward and upward, approaching the articular fossa. Joint spaces can serve as an important observation during the treatment of ADD.

Evaluation of mandibular motions in patients with anterior disc displacement during mouth opening and closing using finite helical axis.

Understanding temporomandibular joint (TMJ) kinematics is essential for the clinical diagnosis and treatment of TMJ disorders. Yet, a comprehensive description of mandibular motion information in patients with anterior disc displacement (ADD) is lacking. The finite helical axis (FHA) is a mathematical model describing the motion of a rigid body in space. This model quantifies mandibular motion patterns by differentiating between rotation around the FHA and translation along it. This study aimed to compare the mandibular motion patterns between patients with ADD and asymptomatic subjects during mouth opening and closing utilizing the FHA. Ten asymptomatic subjects (2 females and 8 males, aged 19-22) and ten patients with ADD (8 females and 2 males, aged 19-57) were tracked using an optical motion tracking system for mouth opening and closing. The FHA during mouth opening and closing was determined from motion trajectory. The distance from the condylar center to the FHA (dCP), the angles between the FHA and the head coordinate system (θx, θy, θz), and the global fluctuation of the FHA spatial orientation (θf) were further calculated. In addition, the helical axis of each frame relative to the initial frame was computed to determine the maximum rotation angle (Θmax) and maximum offset (Tmax) of mandibular motion during mouth opening and closing. It was found that Θmax, Tmax, dLCPmean, dLCPmin, θx, and θf for patients with ADD differed significantly from those of asymptomatic subjects. These findings imply that the FHA effectively describes the disparities between patients with ADD and asymptomatic subjects.

Motion reconstruction and finite element analysis of the temporomandibular joint during swallowing in healthy adults.

There is a close physiological connection between swallowing and the temporomandibular joint (TMJ). However, a shortage of quantitative research on the biomechanical behavior of the TMJ during swallowing exists. The purpose of this study was to reconstruct the movement of the temporomandibular joint (TMJ) based on in vivo experiment and analyze the biomechanical responses during swallowing in healthy adults to investigate the role of the TMJ in swallowing. Motion capture of swallowing, computed tomography (CT), and magnet resonance images (MRI) were performed on six healthy subjects. The movements of the TMJ during swallowing were reconstructed from the motion capture data. The three-dimensional finite element model was constructed. The dynamic finite element analysis of the swallowing process was performed based on the motion data. The range of condylar displacement was within 1 mm in all subjects. The left and right condyle movements were asymmetrical in two-thirds of the subjects. The peak stresses of the discs were relatively low, with a maximum of 0.11 MPa. During swallowing, the condylar displacement showed two trends: slow retraction and slow extension. The tendency to extend could lead to a gradual increase in stress on the disc.

Temporomandibular joint stress analysis of patients with different mandibular deformities during unilateral molar occlusion.

Mandibular prognathism, retrusion and deviation are common mandibular deformities. They can lead to functional and aesthetic problems due to their important role in the oral system. Different from other occlusions, unilateral molar occlusion often occurs during mastication, which has a deep impact on the functions of temporomandibular joints (TMJs). Therefore, the study of unilateral molar occlusion is of great importance and significance to the daily life of patients with mandibular deformities. A total of 35 individuals were involved in this study, including 11 asymptomatic subjects, 10 patients with mandibular prognathism, 5 patients with mandibular retrusion and 9 patients with mandibular deviation. Finite element (FE) models corresponding to the unilateral molar occlusion were constructed. During unilateral molar occlusion, mandibular deformity increases the pressure on the condyle and articular disc. Compared with mandibular protrusion or retraction, facial asymmetry will significantly increase the stress of TMJ. Chewing on the non-deviated side also will lead to higher stress in the TMJ of patients with mandibular deviation. Therefore, patients with mandibular deviation have the highest risk of temporomandibular disorder (TMD), and it is recommended that patients with mandibular deviation chew bilaterally or with the deviated side.

Biomechanical study of temporomandibular joints of patients with temporomandibular disorders under incisal clenching: A finite element analysis.

Temporomandibular disorders (TMD) encompass a collection of pathologies. Within the multitude of etiological factors contributing to TMD, mechanical factors hold significant importance. The aim of this investigation was to assess the magnitude and distribution of stresses encountered by the temporomandibular joints (TMJs) during incisal clenching among TMD patients while also elucidating the mechanical pathogenesis underlying TMD. Ten asymptomatic subjects and ten TMD patients were recruited. The Control, Bilateral, and Unilateral groups were set. The contact stress, maximum principal stress, and minimum principal stresses of TMJ structures among the groups were compared. In addition, comparisons of the contact stress distribution among the groups were adopted. In the Control and Bilateral groups, the magnitudes of stresses (contact stress, maximum and minimum principal stresses) between the right and left sides showed no significant difference (P > 0.05). For unilateral TMD patients,the minimum principal stress on the condyle in the Uni-N group (the normal side) was significantly greater than thatin the Uni-T group (the TMD side)(P = 0.016, mean difference 9.99 MPa [95 %CI: 3.11 to 16.87]). Furthermore, stresses on the condyle and fossa of the patients were significantly greater than those of asymptomatic subjects (P < 0.05). The contact stress distributions were concentrated in the Control group while irregular in the TMD groups. In conclusion, asymmetrical contact stress distributions were observed in unilateral TMD, with excessive stresses on the healthy side. The protection of the healthy TMJ during treatment is recommended for patients with unilateral TMD.

The biomechanical effects of bilateral sagittal split ramus osteotomy and bimaxillary osteotomies to the patients with maxillofacial deformities under incisal clenching.

OBJECTIVE: Bilateral sagittal split ramus osteotomy (BSSRO) and bimaxillary osteotomies (BSSRO plus Lefort1 osteotomy) are widely used to solve maxillofacial deformities. The effect of the surgeries on the temporomandibular joint (TMJ) is still not clear. The purpose of this study was to investigate the preoperative and postoperative stress environment of the patients and to compare the biomechanical differences of the two surgeries. METHODS: Ten patients were performed BSSRO and fourteen underwent bimaxillary osteotomies. Eleven asymptomatic subjects were recruited to be the control group. The muscle forces of incisal clenching were applied on the finite element models. And contact was used to simulate the interactions within the TMJs. RESULTS: two kinds of surgeries could not completely eliminate the negative biomechanical distribution within the TMJs. CONCLUSION: Compared to BSSRO only, the bimaxillary osteotomies could better repair the biomechanical environment of the TMJs under incisal clenching. And the TMD symptoms were strongly related to the stress distributions of the TMJs.

Morphological analysis of the temporomandibular joint in patients with anterior disc displacement.

This study aims to investigate the morphological characteristics of the temporomandibular joint (TMJ) in the patients with anterior disc displacement with reduction (ADDwR) and the alterations after occlusal splint treatment. Thirty ADDwR patients and ten asymptomatic subjects were recruited. Thirteen parameters were adopted, along with automatic computation and presentation of the joint space to characterize the TMJ morphologies. Statistical results showed that morphological discrepancies between the patients and the asymptomatic subjects were ubiquitous. The adjustment of condyle position through occlusal splint treatment can result in joint spaces widening and has positive effects on mitigating the conditions of ADDwR.

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.

Effect of pre-stress on dynamic finite element analysis of the temporomandibular joint.

The pre-stress of the temporomandibular joint (TMJ) at the intercuspal position (ICP) was often neglected, which would cause errors in the finite element analysis. The purpose of this study was to investigate the effect of pre-stress on dynamic finite element analysis of the TMJs. One healthy female adult was recruited for medical imaging and motion data acquisition of the reference position (RP) to the ICP and the clicking teeth. The three-dimensional maxillofacial model including the maxilla, mandible, articular cartilages, discs, and discal attachments was reconstructed. Motion from the RP to the ICP was simulated to obtain pre-stress at the ICP. Two groups of the clicking teeth were simulated: (1) the group without pre-stress (GWoP); (2) the group with pre-stress (GwP). Significant differences were found between the two groups at the initial moment of movement, during the open-mouth phase, and during the collision phase between the upper and lower teeth. The maximum difference in the discal contact stress between both groups was even more than double. The relaxation of the TMJ at the beginning of the mouth opening was simulated in the GwP. In addition, an increase in the TMJ stress during teeth tapping was simulated in the GwP. These were not reflected in the GWoP. If pre-stress at the ICP was not considered, part of the true results would be lost. It is necessary to consider pre-stress in the dynamic finite element analysis of the TMJ.

The effects of the size and strength of food on jaw motion and temporomandibular joints.

Mastication displays much importance in people's lives. The masticatory mandibular motion associated with dental kinematics also impacts temporomandibular joint (TMJ) kinematics and even TMJ health status. How food properties impact kinematical parameters of TMJs is a meaningful question for the conservative treatment of temporomandibular disorders (TMD) and evidence for the diet recommendation of TMD patients. The aim of this study was to find the primary mechanical properties influencing the masticatory motion. The potato boluses with different boiling times and sizes were chosen. The optical motion tracking system was adopted to record the masticatory trials of chewing boluses with various mechanical properties. The mechanical experiments revealed that increasing boiling time could reduce compressive strength. Moreover, multiple regression models were built to find the primary property of food influencing the TMJ kinematics, including condylar displacement, velocity, acceleration, and crushing time. The results showed that the bolus size had a significant primary influence on condylar displacements. The chewing times had a significantly minor influence on condylar displacements, while bolus strength had only a small impact on condylar displacements. Furthermore, condylar displacements on the non-working side were more affected by bolus size and chewing times than on the working sides. The crushing time of the bolus was significantly influenced by the compressive strength. Meals with small sizes and soft properties were therefore advised to lessen condylar displacements and relax the crushing process, and further reduce the loadings in the TMJ.

Effect of bimaxillary surgery on the stress distributions in patients with mandibular retrognathia under unilateral molar clenching.

To investigate the effect of bimaxillary surgery on the stress distribution of the temporomandibular joint (TMJ) in patients with mandibular retrognathia under unilateral molar clenching (UMC). Five patients with mandibular retrognathia (preoperative group) and ten asymptomatic subjects (control group) were recruited. In addition, patients treated with bimaxillary surgery were considered as the postoperative group. The muscle forces corresponding to UMC were applied. The results showed that the discal stresses in the postoperative group were significantly greater than those in the preoperative and control groups. Bimaxillary surgery plus UMC had a detrimental effect on the TMJ.

The influence of maxillary incisor angles on the stress distributions of temporomandibular joints under incisal biting.

BACKGROUND AND OBJECTIVE: The incisal biting was one of the most regular jaw activities. The direction of bite force on the incisor tip and the mandible position were relevant to the incisor angle as biting. This study was carried out to explore the influence on the temporomandibular joint (TMJ) caused by the incisor angle. METHODS: Twenty individuals belonging to three incisor subtypes of the buccal type were recruited. In addition, the 3D models including the maxillary, mandible and discs were established based on their cone-beam computed tomography and magnetic resonance imaging scannings. Then, the mandibular ligaments and the discal attachments were simulated in the finite element models to analyze the stress distributions of the TMJs under incisal biting. RESULTS: The TMJ stresses of subtype I showed normal range and distribution. The stresses of the intermediate temporal bone tended to increase in subtype II. The intermediate and posterior bands of the discs sustained greater tensile stresses in subtype III. CONCLUSIONS: Abnormal stress distributions are harmful to TMJs, so the incisor cusp was not suggested to incline to the palatal side too much.

An Improved Finite Element Model of Temporomandibular Joint in Maxillofacial System: Experimental Validation.

Finite element (FE) analysis has become a popular method of exploring the biomechanical characteristics of temporomandibular joint (TMJ). However, the FE model should be improved and its reliability should be verified further. This study developed a complete maxillofacial model by cone-beam computed tomography (CBCT) and magnetic resonance imaging (MRI). The integrity and physiological environment of TMJ were considered. Then the FE model and corresponding 3D printed model were developed and loaded under the same conditions. The strains on the mandible and upper surface of the left articular disc were measured on the experimental model and compared with the FE model. The differences of the strains on the mandible were less than 6%. The strain distributions on the disc were also approximate between the experimental and simulated results. It indicated that the strains calculated from the improved FE model were reliable on the mandible and inside the TMJ.

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.

Biomechanical comparison of the effect of bilateral sagittal split ramus osteotomy with or without Le Fort I osteotomy on the temporomandibular joints of the patients with maxillofacial deformities under centric occlusion.

Mandibular deformities negatively affect the daily activities of the patients and may cause temporomandibular disorders (TMD). Bilateral sagittal split ramus osteotomy (BSSRO) and Le Fort I osteotomy are effective treatments to correct the mandibular deformities. The aim of this study was to investigate and compare the effects of the BSSRO with or without Le Fort I on the stress distributions of the temporomandibular joints (TMJs) of the patients with mandibular deformities under centric occlusion based on finite element (FE) method. Preoperative and postoperative cone-beam computed tomography (CBCT) images of twenty-four patients diagnosed with mandibular prognathism, including ten patients with BSSRO and another 14 patients with bimaxillary osteotomy (BSSRO with Le Fort I), were used to construct maxillofacial models. Ten asymptomatic individuals were also performed CBCT scanning and defined as the control group. In addition, the muscle forces and boundary conditions corresponding to centric occlusions were applied on each model. For the preoperative groups with both the BSSRO and bimaxillary osteotomies, the average peak contact stresses of the TMJs were both greater than those of the control group. After the surgeries, the contact stresses of the discs and temporal bones of both groups considerably decreased. However, the contact stresses on the condyles slightly increased after BSSRO but decreased after bimaxillary osteotomy. The TMJs of the patients with maxillofacial deformities suffered abnormal tensile and compressive stresses compared with the asymptomatic subjects under centric occlusion. Both of the BSSRO and bimaxillary osteotomy could improve the risk stress distributions of the TMJs.

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.

Descriptions of the dynamic joint space of the temporomandibular joint.

BACKGROUND: Clinical diagnosis and treatment depended heavily on the motion analysis of the human joints. Although the dynamic joint space (DJS) of other organs was widely used in academic investigations, they were not universally used in the temporomandibular joint (TMJ) field, which was also important for the motion evaluation of the TMJ. The objectives of this study are to introduce the DJS of the TMJ and characterize the DJS regulars of mandibular movements. METHODS: Ten asymptomatic subjects were selected to instruct this application. The mouth opening and closing, mandibular protrusion, and left and right protrusions, were tracked by the optical motion tracking system. According to trajectories of markers and reconstructed models from computed tomography, the motions of the mandibles could be obtained. The DJSes, which were described as the minimum Euclidian distances, were subsequently calculated based on the geometrical surfaces between the condyle and fossa during the motions. Then, the DJS map could be drawn based on the calculated values. RESULTS: The DJS map manifested a decreasing trend when the condyle crossed the glenoid fossa, while it generally increased after the condyle crossed the fossa during the mouth opening. The results showed that the average maximum and minimum anterior joint spaces were 5.39 mm and 2.07 mm during mouth opening respectively with a great discrepancy existing among the subjects. The average maximum and minimum anterior joint spaces were 4.74 mm and 2.19 mm during mandibular protrusion. As for left and right protrusions, the DJS of the contralateral side was greater than that of the ipsilateral side. CONCLUSION: In comparison to morphological analyses or only mandibular motions, the DJS provides more dynamic and interactive information about the TMJ. The research and methodology may help us comprehend TMJ motions and temporomandibular disorders.

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.

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.