Orthodontic Treatment is based on the principle that if prolonged pressure is applied to a tooth, tooth movement will occur as the bone around the tooth remodels. Bone is selectively removed in some areas & added in others. In essence, the tooth moves through the bone carrying its attachment apparatus with it, as the socket of the tooth migrates. Because the bony response is mediated by the periodontal ligament, tooth movement is primarily a periodontal ligament phenomenon.