Orthodontic treatment is one of the most common types of dental treatment. Research indicates that many people need some degree of such treatment. Therefore, in the past several decades, orthodontics has developed rapidIy. Various facts about the subject have been discovered and new technologies are continuously being developed. However, the treatment time has stayed more or less the same in the past decades. Due to the complexity and the various factors involved in the treatment, orthodontists are still investigating the mechanism of orthodontic tooth movement, such as the relationship between the applied force magnitude and the rate of tooth movement. Few attempts have been made to develop a constitutive law that can predict the orthodontic tooth movement. Such a law will give insights to means of improving the orthodontic treatment. The objective of this research is to deveIop a constitutive law relating the force magnitude and the amount of orthodontic tooth movement and establish ways for the improvement of the treatment. Existing knowledge on the mechanism of orthodontic tooth movement was first gathered to develop the constitutive law, which incorporates the influence of various factors such as bone density, time dependent behavior of biological response, age, etc. Then a finite element simulation was performed. A parametric study was carried out to benchmark the model and study the effect of various parameters. The model fits the experimental data quite well and agrees with the trend of clinical cases. The results indicate that a force level producing a stress just below certain threshold stress can move the tooth faster without causing too much necrosis of the PDL and that the superelasticity of shape memory alloys can be further utilized to decrease the load deflection rate and maintain a constant moment to force ratio, which would enhance the control of orthodontic tooth movement.