Thorough understanding of the biomechanical force systems generated by orthodontic archwire activations is important for producing efficient tooth movement directed toward achieving predetermined treatment goals. This information is also essential for accurate interpretation of the biological responses to orthodontic appliances. Clinical trends are toward an increased use of wires with a greater range of action by appliances constructed of new materials and with longer interbracket spans. This enables an orthodontic appliance to remain active for longer periods of time between appointments but also magnifies the unwanted side-effects of inaccurately conceived appliance activations. It is therefore important to know more precisely the forces and moments produced by orthodontic wire activations. Previous studies have examined tooth movement and the force systems producing it from a two-dimensional perspective. Most orthodontic appliances, however, act in all planes of space. This study is aimed at better defining the three-dimensional forces and moments produced by three-dimensional orthodontic appliances. A three-dimensional finite element model is proposed to analyze the force systems developed by fully- contoured orthodontic archwires. The study will describe differences between a two-dimensional and three-dimensional analysis of the forces and moments produced by a three-dimensional, rectangular orthodontic archwire inserted at the molars and incisors. The importance of considering the different properties of various compositions of orthodontic archwires acting primarily in bending versus torsion will be examined by varying the cross-sectional dimensions of the wires being tested and comparing the effective force systems produced at the molars versus the incisors. The effect of dental arch shape will also be studied by comparing ideal arch form configurations with those that are more square or more tapered.
