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

Effect of Various Degrees of Anterior Disc Displacement on the Biomechanical Response of the Masticatory System

Anterior disc displacement (ADD) is one of the most prevalent temporomandibular disorders (TMD). It was widely recognized that occlusal factors could affect temporomandibular joint (TMJ). However, the impacts of ADD on the biomechanical environment of TMJ and occlusion are still unclear. This study aimed to describe the effects of ADD on the masticatory system, including TMJ and occlusion. The finite element model (FEM) was constructed based on the medical images of a healthy adult male. The complete skull, masticatory muscles, TMJs, and related ligaments were included. Three FEMs with different degrees of ADD were constructed with disc-condyle angles of 10 deg, 20 deg, and 30 deg. The muscle forces corresponding to intercuspal clenching (ICC) were applied as the loading condition. Four models were conducted: normal, mild, moderate, and severe ADD. It was found that the overall stress distribution was relatively consistent across the four models. The contact stress on the TMJ and occlusion in severe ADD was visibly different from the other three models. In addition, the contact stress on the condyle gradually increased with the increasing occlusal strength. Abnormally high-stress concentration began to appear on the condyle at 30% muscle strength. Moderate ADD was more of a transitional stage. Compared to mild and moderate ADD, severe ADD had visibly effects on the stress response of the TMJ and the entire mandible (including occlusion), such as abnormally high stresses of the condyle, stress concentration on the second molar, and prone to disc extrusion and anterior slippage during high-strength occlusion.

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.

Heterogeneous material models for finite element analysis of the human mandible bone - A systematic review

Subject-specific finite element (FE) modeling of the mandible bone has recently gained attention for its higher accuracy. A critical modeling factor is including personalized material properties from medical images especially when bone quality has to be respected. However, there is no consensus on the material model for the mandible that realistically estimates the Young's modulus of the bone. Therefore, the present study aims to review FE studies employing heterogeneous material modeling of the human mandible bone, synthesizing these models, investigating their origins, and assessing their risk of bias. A systematic review using PRISMA guidelines was conducted on publications before 1st July 2024, involving PubMed, Scopus, and Web of Science. The search string considered (a) anatomical site (b) modeling strategy, and (c) metrics of interest. Two inclusion and five exclusion criteria were defined. A review of 77 FE studies identified 12 distinct heterogeneous material models, built based on different in vitro or computational methodologies leading to varied performance and highly deviated range of estimated Young's modulus. They are proposed for bones from five different anatomical sites than mandible and for both trabecular and cortical bone domains. The original studies were characterized with a low to medium risk of bias. This review assessed the current state of material modeling for subject-specific FE models in the craniomaxillofacial field. Recommendations are provided to support researchers in selecting density-modulus relationships. Future research should focus on standardizing experimental protocols, validating models through combined simulation and experimental approaches, and investigating the anisotropic behaviour of the mandible bone.

Differential impact of chronic intermittent hypoxia and stress changes on condylar development

OBJECTIVES

This study aimed to determine the effects of chronic intermittent hypoxia (CIH) and stress change (SC) on the development of the condyle in mouth breathing rats.

DESIGN

A total of 120 4-week-old rats were randomly assigned to one of five groups. The control (Ctrl) group was the blank control and the intermittent nasal obstruction (INO) group was the positive control. Mild CIH (mCIH) and severe CIH (sCIH) groups were developed by adjusting environmental oxygen concentration and monitoring real-time blood oxygen saturation (SpO2). The SC group was developed using INO, increased environmental oxygen concentration, and real-time SpO2 monitoring. Six rats from each group were sacrificed for analysis at 0, 1, 2, or 4 weeks.

RESULTS

Similar to the INO group, condyle and mandibular body development in the sCIH group, but not in the mCIH group, was significantly inhibited compared with the Ctrl group. The SC group had inhibited development of the condyle, especially of the posterior zone, but had minimal impact on the growth of the mandible.

CONCLUSION

The inhibitory effects of CIH on the development of the condyle and mandibular body were SpO2-dose-dependent. When SC occurred, inhibited development was observed in the posterior zone of condyle but not the whole mandible. These findings provide important insights for targeted interventions that address the consequences of mouth breathing in children.

Biomechanical behavior of temporomandibular joint movements driven by mastication muscles

Surgery of jawbones has a high potential risk of causing complications associated with temporomandibular joint disorder (TMD). The objective of this study was to investigate the effects of two drive modeling methods on the biomechanical behavior of the temporomandibular joint (TMJ) including articular disc during mandibular movements. A finite element (FE) model from a healthy human computed tomography was used to evaluate TMJ dynamic using two methods, namely, a conventional spatial-oriented method (displacement-driven) and a compliant muscle-initiated method (masticatory muscle-driven). The same virtual FE model was 3D printed and a custom designed experimental platform was established to validate the accuracy of experimental and theoretical results of the TMJ biomechanics during mandibular movements. The results show that stress distributed to TMJ and articular disc from mandibular movements provided better representation from the muscle-driving approach than those of the displacement-driven modeling. The simulation and experimental data exhibited significant strong correlations during opening, protrusion, and laterotrusion (with canonical correlation coefficients of 0.994, 0.993, and 0.932, respectively). The use of muscle-driven modeling holds promise for more accurate forecasting of stress analysis of TMJ and articular disc during mandibular movements. The compliant approach to analyze TMJ dynamics would potentially contribute to clinic diagnosis and prediction of TMD resulting from occlusal disease and jawbone surgery such as orthognathic surgery or tumor resection.

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.

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.

Semi-autonomous two-stage dental robotic technique for zygomatic implants: An in vitro study

OBJECTIVE

To assess the feasibility and accuracy of a semi-autonomous two-stage dental robotic technique for zygomatic implants.

METHODS

Twenty-six zygomatic implants were designed and randomly divided into two groups using 10 three-dimensionally printed resin models with severe maxillary atrophy. In one group, the conventional drilling technique was used, in the other group, the drilling process for the alveolar ridge section (first stage) was completed, after which drilling for the zygoma section (second stage) was done. Based on preoperative planning combined with postoperative cone-beam computed tomography (CBCT), coronal, apical, depth, and angle deviations were measured. Zygomatic implant placement technique-related deviations (sinus slot, intrasinus, and extrasinus) were also recorded and analyzed.

RESULTS

The two-stage technical group's coronal, apical, depth, and angle deviations were 0.57 ± 0.19 mm, 1.07 ± 0.48 mm, 0.30 ± 0.38 mm, and 0.91 ± 0.51°, respectively. The accuracy of the two-stage technique was significantly higher than that of the conventional one-stage technique (p < 0.05). The apical deviation in the intrasinus group was 1.12 ± 0.56 mm, which was significantly better than that in the other two groups (p < 0.05). The angle deviation in the sinus slot group was 1.96 ± 0.83°, which was significantly worse than that in the other two groups (p < 0.05).

CONCLUSION

Using the semi-autonomous two-stage dental robotic technique for zygomatic implants is feasible and is more accurate than using the conventional one-stage technique.

CLINICAL SIGNIFICANCE

The two-stage technique enabled the semi-autonomous robot to overcome the mouth-opening restriction for zygomatic implants and improved accuracy.

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.

Variation in stress distribution modified by mandibular material property: a 3D finite element analysis

BACKGROUND

Temporomandibular joint disorder (TMD) is a common oral and maxillary facial disease. Finite element method (FEM) has been widely used in TMD studies. Material assignment significantly affects FEM results. The differences in the methods of material assignment used in previous studies have not been comprehensively assessed for further calculations.

METHODS

The mandible material modelling approaches were of four types, namely: uniform modelling with (A) cortical bone; and (B) cancellous bone; (C) semi-uniform modelling with division of cortical and cancellous bone; and (D) non-uniform modelling with Computed tomography (CT) gray value related modulus. Meanwhile, the Young's modulus of values ranging from 20 to 300 GPa were considered for the teeth. Ten modellings were used to analyze and discuss the differences in contact pressure and contact force.

RESULTS

(1) The increase in teeth elastic modulus increased the maximum contact pressure on the alveolar bone and contact force on teeth, but induced insignificant stress variation on the temporomandibular joint; (2) The location of the maximum contact pressure was steady for all four modelling approaches of the mandibular material. However, the maximum contact pressure and contact force exhibited an insignificant difference.

CONCLUSIONS

Teeth with a higher elastic modulus significantly enhanced the stress concentration in the alveolar bone; in contrast, it induced minor variations in the temporomandibular joint stress states. The extreme stress regions predicted by the four mandibular models were consistent with the actual damaged regions. However, non-uniform modellings based on CT values could better describe the mechanical properties of the human bone, which should be primarily considered.