Descriptions of the dynamic joint space of the temporomandibular joint

Improved stomatognathic model for highly realistic finite element analysis of temporomandibular joint biomechanics

BACKGROUND

Mechanical response analysis of the temporomandibular joint (TMJ) is crucial for understanding the occurrence and development of diseases. However, the realistic modeling of the TMJ remains challenging because of its complex composition and multivariate associations.

OBJECTIVE

This study aims to develop a highly realistic stomatognathic model that accurately represents the geometric accuracy, structural integrity, and material properties. And further optimizes the interference and establishes the application range of the simplifications and the assumptions.

METHODS

Geometric reconstruction of the bone was based on high-resolution image data, with the accuracy of the occlusal surface ensured by plaster cast model registration. Soft tissues such as cartilage, the disc, the periodontal ligament (PDL), and disc attachments often need to be approximated or assumed. Therefore, the finite element methods (FEM) was used to optimize these assumptions, including 1) the biomechanical effects of the thickness and modulus of the PDL, 2) the approximation of the geometry and material behavior of the disc, and 3) the simplification of the loading and boundary conditions.

RESULTS

1) The deformation of the PDL causes tooth movement, which spreads to the distal condyle and further effects the TMJ load situation, 2) Disc reconstructed by MRI and hyperelastic material behavior are necessary for accurate TMJ loading analyses, 3) The loss of relative sliding movement between teeth interferes with realistic TMJ loading.

CONCLUSION

The improved stomatognathic model delivers highly realistic and validated simulation, offering theoretical guidance for virtual treatments and TMJ multivariate overload studies.

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.

Altered dynamic joint space in the lateral condyle compartment following medial unicompartmental knee arthroplasty

PURPOSE

The progression of osteoarthritis in lateral compartment has been identified as a primary complication in medial unicompartmental knee arthroplasty (UKA) revisions, irrespective of whether employing fixed bearing (FB) or mobile bearing (MB) designs. Compared to the previous contact point analyses, the tibiofemoral contacts during knee movements are comprehended by a more comprehensive understanding of joint spaces. This study aims to dynamically map the joint spaces in the lateral compartment during the single-leg lunge following FB and MB UKA procedures, and compare them with the respective contralateral native knees. It is hypothesized that the significant change in joint space for post-UKA compared to their native knees.

METHODS

Twelve patients with unilateral medial FB UKA and eleven patients with unilateral medial MB UKA were included and underwent computed tomography scans. The exclusion criteria included anterior cruciate ligament deficiency, postoperative knee pain, any postoperative complications, and musculoskeletal illnesses. A dual fluoroscopic imaging system was utilized to capture the single-leg lunge, and 2D-to-3D registration facilitated the visualization of knee motion. According to the knee motions, joint spaces on tibial and femoral surfaces in the lateral compartments of native, FB, and MB UKA knees were calculated and mapped.

RESULTS

In comparison to the native knees, FB UKA knees exhibited significant increases in medial, lateral, central, and posterior joint spaces in the lateral compartment (p < 0.05), while MB UKA knees showed significant increases only in central and posterior joint spaces (p < 0.05). Moreover, FB UKA demonstrated greater increases in medial, central, and posterior joint spaces compared to MB UKA. Tibial varus and valgus during lunges, as well as the Oxford Knee Score (OKS) and Hip-Knee-Ankle angle (HKA), correlated with joint spaces.

CONCLUSIONS

Dynamic joint space analysis provided a more comprehensive insight into contact dynamics. FB UKA led to an enlargement of joint spaces, whereas MB UKA resulted in joint spaces closer to native knees. These findings contribute to understanding potential postoperative complication in UKAs.

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.

Investigation of the accuracy of dynamic condylar position: A model study

OBJECTIVES

To evaluate dynamic condylar positions by integrating mandibular movement recording data and cone-beam computed tomography (CBCT) and to investigate its accuracy via dynamic model experiments.

METHODS

A polyvinyl chloride skull model was utilized. A robot arm was used to operate the mandible to perform mouth opening, closing, protrusion, and lateral movements. A recording device, worn on the skull, was used to record the dynamic process and an optical position tracking (OPT) system was used to simultaneously trace the movements. A self-developed software module was used to evaluate the dynamic condylar position by integrating the dynamic tracing data and a virtual skull model derived from CBCT images. Errors were defined as differences between the dynamic coordinates of six landmarks around the condylar area derived from the software module (test) and OPT system (gold standard).

RESULTS

The condylar position errors were 0.76 ± 0.31, 0.55 ± 0.15, and 0.68 ± 0.23 mm for mouth opening, bilateral, and protrusion movements, respectively. Furthermore, the errors for small, moderate, and large mouth opening movements were 0.62 ± 0.19, 0.69 ± 0.29, and 0.94 ± 0.31 mm, respectively. The errors for all movements, except for large mouth opening, were significantly less than 1 mm (P < 0.05). The error was not different from 1 mm in the large mouth opening movement (P > 0.05).

CONCLUSIONS

Our developed method of achieving dynamic condylar position by integrating mandibular movement recording data and CBCT images is clinically reliable.

CLINICAL SIGNIFICANCE

This study proved the reliability of evaluating dynamic condylar position using a commercial dynamic recording instrument and CBCT images.