Biphasic theory of tooth movement: Cytokine expression and rate of tooth movement: Cytokines and rate of tooth movement

Understanding the molecular and cellular events during orthodontic tooth movement can greatly impact daily orthodontic practice. Selecting the most appropriate force magnitude, knowing precise tooth movement, optimizing activation intervals, preventing side effects, and, most importantly, developing techniques that increase the rate of tooth movement are all infl uenced by this understanding. These events can be divided into two main phases, a catabolic phase, where osteoclast-driven bone resorption determines the rate of tooth movement, and an anabolic phase, where osteoblast-driven bone formation reestablishes and maintains alveolar bone integrity of the new occlusion. These two phases are not simultaneous or independent - the catabolic phase is required and always precedes the anabolic phase. We call this biological phenomenon the Biphasic Theory of Tooth Movement. While cytokines play an important role in initiating the catabolic phase, interaction between osteoclasts and osteoblasts regulates the anabolic phase. Therefore, to increase the rate of tooth movement, acceleration techniques must focus fi rst on producing higher cytokine activity and second on enhancing osteoclast and osteoblast interactions to expand the boundary of tooth movement and maintain the integrity of alveolar bone in the newly established occlusion. In this chapter, we will review the events of both catabolic and anabolic phases of treatment and how to manipulate them to enhance orthodontic outcomes.