Laboratory evaluation of orthodontic biomechanics: The clinical applications revisited

Finite element analyses (FEA) are used often in the field of Orthodontics. The reliability of FEA depends on the geometry of the structure, the material properties, and the loading configuration. The center of resistance is of fundamental importance for the evaluation of movement in Orthodontics. Most simulations for the assessment of the center of resistance involve FEA. Another series of experiments evaluate force and moment from several appliances during orthodontic movement. The Orthodontic Measurement and Simulation System is used in many of these studies. Especially for torque quantification, several bracket/archwire configurations have been tested on multiple devices, however biomechanical differences render difficult the direct comparison of the results. Further, friction during sliding mechanics has been extensively investigated in the laboratory. These ex-vivo friction research protocols show poor reliability, since several different mechanisms are involved in resistance to sliding. A critical appraisal of the literature revealed that in-vitro trials are no substitute for clinical testing and the results of most ex-vivo investigations should not be extrapolated in the clinical practice without skepticism.