[Concept for development of new individual treatment devices in orthodontics using 3-dimensional numerical simulation of bone remodeling]

Finite Element Calculation of Bone Remodeling in Orthodontics by Using Forces and Moments

Orthodontic appliances induce bone remodeling by acting as systems of forces and moments onto the crown of a tooth. These forces and moments should be within low physiological range to avoid resorptions. This is often realized by the use of superelastic wires or springs. For improving the design of these devices, we use the Finite Element Method (FEM) to simulate the behavior of teeth and devices. Great advantages were made in simulating the bone remodeling during the movement of a single tooth. Due to the lack of element types implementing hysteresis in the stress/strain graph, it is difficult to simulate the non-linear material properties of the superelastic wires made of NiTi-alloys. For this reason, we integrated the measurement of the devices into the calculation of the tooth movement. In this study we simulate the orthodontic long-term tooth movement of the canine retraction, using the new hybrid retraction spring.5 This spring allows a well-defined adjustment of the acting force system. The result of this study provides an example of how this approach can be used for future comparison of different orthodontic devices.

Quasi-automatic 3D finite element model generation for individual single-rooted teeth and periodontal ligament

The paper demonstrates how to generate an individual 3D volume model of a human single-rooted tooth using an automatic workflow. It can be implemented into finite element simulation. In several computational steps, computed tomography data of patients are used to obtain the global coordinates of the tooth's surface. First, the large number of geometric data is processed with several self-developed algorithms for a significant reduction. The most important task is to keep geometrical information of the real tooth. The second main part includes the creation of the volume model for tooth and periodontal ligament (PDL). This is realized with a continuous free form surface of the tooth based on the remaining points. Generating such irregular objects for numerical use in biomechanical research normally requires enormous manual effort and time. The finite element mesh of the tooth, consisting of hexahedral elements, is composed of different materials: dentin, PDL and surrounding alveolar bone. It is capable of simulating tooth movement in a finite element analysis and may give valuable information for a clinical approach without the restrictions of tetrahedral elements. The mesh generator of FE software ANSYS executed the mesh process for hexahedral elements successfully.