Acceleration of tooth movement

New approaches to shorten treatment time without foregoing optimal results, has become a primary goal of all areas of orthodontics. Low friction and self-ligating bracket systems, preformed archwires, alveolar corticotomies are some examples. The phases of normal tooth movement are (Burstone 1962) 1. Initial phase, 2. Lag phase 3.Post lag /continuous phase. When a force is applied onto a tooth, it results in a number of biophysical events such as compression of periodontal ligament, bone deformation and tissue injury. These biophysical events in turn lead to certain biochemical reactions at a cellular level which bring about bone remodelling. Bone deformation and compression of the periodontal ligament leads to the release of some extra-cellular signaling molecules called first messengers. Hormones such as parathormone, local chemical mediators such as prostaglandins and neurotransmitters such as substance P and vasoactive intestinal polypeptide (VIP). The first messengers bind to receptors present on the cell surface of target cells and initiate a process of intracellular signalling. The intra-cellular signalling results in formation of second messengers, which include cyclic AMP, cyclic GMP and calcium. Second messengers inside the cells is believed to initiate formation of bone cells namely osteoclasts and osteoblasts which are responsible for bone remodelling. Mechanical forces, at present the only clinical means for producing orthodontic tooth movement, are but one way to activate cells. Chemical and physical agents are capable of stimulating bone cells to perform specific functions. Cellular activation occurs in or through the cell membrane. It involves fluxes of ions, such as Ca2+, Mg2+, Na+, K+, Cl, and inorganic phosphate as well as activation of the membrane-bound enzymes adenylate cyclase and guanylate cyclase. Enzymes act upon their respective substrates, adenosine triphosphate (ATP) and guanosine triphosphate (GTP), to produce adenosine 3’, 5’-monophosphate (cAMP) and guanosine 3’, 5’-monophosphate (cGMP). These latter substances, together with Ca2+, are considered to be the intracellular “second messengers” which mediate the effects of external stimuli on their target cells. All three substances serve as co-factors in enzymatic phosphorylation reactions. The rational of acceleration by physical stimulation concomitant with orthodontic forces is done in order to augment the effect of the mechanical forces. Tissue remodeling effect which is mediated by a variety of cells like fibroblasts, root and bone surface lining cells endothelial and epithelial cells and different kinds of leukocytes. Thus this method is helpful in increasing the speed of tooth movement. The chemical methods to accelerate the rate of orthodontic tooth movement includes application of pharmacologic agents have shown good results in increasing orthodontic tooth movement .The combined effect of force application and the exogenous administration of an osteoclast differentiation factor has an effect on the rate of orthodontic tooth movement and periodontal ligament gene expression. In surgical method of corticotomy were linear cuts and bur holes are made extending 0.5mm into the medullary bone results in a temporary burst of localized soft and hard tissue remodeling (i.e., regeneration) which rebuilds the bone back to its normal state. Rapid tooth movement was due to transient localised demineralization and remineralisation in the bone due to wound healing. This phenomenon is known as the regional acceleratory phenomenon (RAP). This article presents a detailed description of the various methods of acceleration of tooth movement.