SCIENCE UP THE WORLD
15TH INTERNATIONAL STUDENT CONGRESS OF MEDICAL SCIENCES
JUNE 3RD - 6TH 2008
Yijin Ren
The Essence of Orthodontic ForceDepartment of Orthodontics, University Medical Centre Groningen The application of orthodontic force triggers the biological system of periodontal tissues resulting in tooth movement. Different opinions exist about the force level that results in optimal mechanical conditions for orthodontic intervention. It is assumed that an optimal force system is important for an adequate biological response in the periodontal ligament. In the past 70 years, the concept of optimal force has changed considerably. The current concept of optimal force is based on the hypothesis that a force of a certain magnitude and temporal characteristics would be capable of producing a maximum rate of tooth movement without tissue damage and with maximum patient comfort. The optimal force for tooth movement may differ for each tooth and for each individual patient. The magnitude of force has received significant attention in orthodontics without considering that it is important only because it is related to other characteristics of the force system and surface area of the periodontal ligament over which it is dissipated. The forces, which are applied to the crowns of the teeth, are distributed over the entire supporting structure and so are the stresses and strains. From a cellular point of view, distribution of stress (force per unit area), distortion of the periodontal ligament (shear stress, strain), and bone deformation (strain) are critical factors, and the remodelling response is directly related to stress and strain levels within the periodontium. The orthodontic force as an extrinsic mechanical stimulus thus evokes a biologic cellular response that aims to restore equilibrium by remodelling of the periodontal supporting tissues. Because it is very difficult to measure stresses and strains within the periodontal ligament of loaded teeth directly, only measuring the forces that are applied directly to teeth with known root surface areas can provide an estimate of these parameters.A thorough systematic review of the available literature on this topic could be a basis for the application of appropriate forces in clinical orthodontics. When the outcome of such a review was not enough for a meta-analysis, a mathematical analysis of the results across a group of studies with common underlying characteristics, appears to be the alternative choice. This presentation will address several key issues in the relation between orthodontic force and the rate of tooth movement and, more specifically, at the assessment of an optimal force or force range for clinical use in orthodontics based on a systematic review and a mathematical modelling on data from standardized animal experiments.
