The rate and the type of orthodontic tooth movement is influenced by bone turnover in a rat model

The influence of bone metabolism on both the rate and the type of orthodontic tooth movement was investigated. A rat model in which high (n = 16) and low (n = 17) bone turnover was pharmacologically induced was used. A non-pharmacologically treated group (n = 19) served as the control. A mesially directed constant single force of 25 cN was applied to the upper left first molar for a period of 3 weeks. The study was performed as a split-mouth design, the contralateral side of each animal serving as its control. The displacement of the molar crown was measured with an electronic calliper, while changes in inclination of the teeth were measured from micro-CT scans of the excised maxillae. The bone turnover significantly affected the rate of tooth movement. In the case of high turnover, the rate of tooth movement was increased while it was reduced in the case of low turnover. A controlled mesial tipping in all th ree groups was observed, but the actual location of the centre of rotation seemed to be influenced by the metabolic state of the bone. Based on the results it can be concluded that deviations in bone turnover influence the response to orthodontic forces, and should be taken into consideration when planning orthodontic treatment in patients with metabolic bone disease or those on chronic medication influencing bone metabolism.