Finite element modeling of TMJ joint disc behavior.

INTRODUCTION: On account of its specific biodynamics, the disc joint located at the very heart of the joint can impact every constituent of the manducatory system. The disc is deformed when subjected to stresses exerted by the muscles of mastication which it partly absorbs and partly redistributes. MATERIALS AND METHODS: CT-scan slices and MRI images of a subject were made in order to create a finite element anatomical model of the TMJ. The forces applied to the subject's joint model were obtained by performing vector decomposition of the maximum muscle forces produced by this individual. The resultant force in this study was subjected to different frequencies approximating those observed in mastication. RESULTS: The reaction force at the glenoid fossa can reach up to 1035 N depending on the frequency of the indentation. Generally, during the different exercises, the areas of maximum stress were located at the lateral portion of the disc and on the posterior band. They reached forces up to 13.2 MPa following a 32 s exercise at a frequency of 0.5 Hz. DISCUSSION: Even if the behavior law needs to be improved, joint resiliency was demonstrated in this study. The areas of maximum stress were equivalent in the different exercises on account of the anatomy of the different parts and the axis of the forces applied. This study offers food for thought regarding joint disorders and opens the way for further research to complement the current investigation.

Anticipating root displacements: unlocking new prospects.

OBJECTIVE: The aim of this study was to visualize and quantify root displacements in the bone base of a patient before orthodontic treatment and obtain an optimal set-up that would include information on both coronal and root movements. MATERIAL AND METHOD: Data from a patient's scan records, the initial plaster model and scanned set-up are migrated into the Amira® software for advanced mesh and surface analysis. Using this software, each tooth of the initial 3D-reconstruction scan is isolated then superimposed over that of the initial model. The set-up is then positioned onto the initial model at second molar level and dragged onto the initial 3D reconstruction. Lastly, the roots are repositioned on the crowns on the set-up. RESULTS: This study enabled the visualization and quantification of dental displacements (crowns and roots) from initial to expected final position in a three-dimensional space reconstruction. DISCUSSION-CONCLUSION: This technique, carried out routinely thanks to the advent of cone beam tomography, can help optimize orthodontic treatments, notably by anticipating root proximity issues during set-up preparation.

Finite element modelling of the articular disc behaviour of the temporo-mandibular joint under dynamic loads.

The proposed biodynamic model of the articular disc joint has the ability to affect directly the complete chewing mechanism process and its related muscles defining its kinematics. When subjected to stresses from the mastication muscles, the disc absorbs one part and redistributes the other to become completely distorted. To develop a realistic model of this intricate joint a CT scan and MRI images from a patient were obtained to create sections (layers) and MRI images to create an anatomical joint CAD model, and its corresponding mesh element using a finite element method. The boundary conditions are described by the external forces applied to the joint model through a decomposition of the maximum muscular force developed by the same individual. In this study, the maximum force was operating at frequencies close to the actual chewing frequency measured through a cyclic loading condition. The reaction force at the glenoid fossa was found to be around 1035 N and is directly related to the frequency of indentation. It is also shown that over the years the areas of maximum stresses are located at the lateral portion of the disc and on its posterior rim. These forces can reach 13.2 MPa after a period of 32 seconds (s) at a frequency of 0.5 Hz. An important part of this study is to highlight resilience and the areas where stresses are at their maximum. This study provides a novel approach to improve the understanding of this complex joint, as well as to assess the different pathologies associated with the disc disease that would be difficult to study otherwise.