Abstract
This study was performed to investigate the effect of age on the efficiency of orthodontic tooth movement based on critical literature reviews, studies on a standardized orthodontic animal model and a non-invasive clinical investigation. A systematic review was performed on the optimum force for orthodontic tooth movement. It appeared that no evidence about the optimal force level in orthodontics could be extracted from literature. Therefore, a mathematic model that was developed to describe the relation between the rate of orthodontic tooth movement and the magnitude of the applied force. The results showed that the maximum rates of tooth movement in humans and in dogs are very similar. A threshold for force magnitude that would switch on tooth movement could not be defined. As there are general drawbacks in literature using rat as a model for experimental tooth movement, a newly designed experimental appliance for tooth movement in rats was proposed and evaluated. This rat model was used then for the study of age effect on orthodontic tooth movement. The results showed a faster initial tooth movement in juvenile than in adult animals. But once tooth movement had reached the linear phase, the rate of tooth movement was the same in both groups. Further study on osteoclast differentiation indicated that orthodontic forces induced faster osteoclast differentiation in young rats. These results agree with a later clinical study on crevicular fluid that in early tooth movement cytokine levels in juveniles are more responsive than in adults. In the end results from the different studies were related and extrapolated. Suggestions for evidence-based research were proposed, specifically, perspectives in GCF studies and future orthodontic research were discussed
