Tooth movement with light continuous and discontinuous forces in beagle dogs

In orthodontics, no consensus exists on how to move teeth most efficiently. The aim of the present study was to investigate the effect of two different force regimes and two different force magnitudes on tooth displacement. A split mouth design study was conducted in young adult beagle dogs. In each dog, both mandibular third premolars were extracted, and orthodontic appliances were placed for bodily distalization of the second premolars. The forces (10 cN or 25 cN) were applied, either continuously (24 h a day) or discontinuously (active 16 h daily from 17.00 till 9.00). Individual time-displacement curves of the second premolars were constructed. Four phases of tooth movement could be distinguished. Statistical analysis showed that the choice of regime had an influence on the duration of the hyalinisation phase, while force magnitude had not. The rate of tooth movement in the linear phase was mainly regime dependent. However, force magnitude also appeared to have some influence. The individual tissue response in each dog appeared to have an influence on both the duration of the second phase and the rate in the fourth phase. It was concluded that under these experimental conditions, force regime has more influence on the rate of orthodontic tooth movement than force magnitude.