Biomechanical principles of tooth movement.

The major mechanical signals or stimuli in orthodontic therapy are the stress and the resultant strain or deformation in the periodontal supporting tissues. These signals are translated into biologic cellular activities by some yet unclear mechanisms. Direct action by the stresses and strains upon the cells as well as by secondary effects produced by stresses and strains (such as very low piezoelectric voltage) may occur. The relationship between stress and the rate of tooth movement is not a simple one and is dependent on the stage of tooth movement; there appears to be a monotonically increasing relationship between stress and rate of tooth movement at least for low stress values. Having presented this overview of our present knowledge of biomechanics, fundamentals of cellular dynamics can be developed on the one hand and therapeutic strategies expanded on the other hand by the subsequent articles.