Determination of the centre of resistance during en masse retraction combined with corticotomy: finite element analysis

Objective: To determine the effect of corticotomy on the change in the centre of resistance of the six maxillary anterior teeth

Materials and methods: Three-dimensional finite element models of the maxillary anterior teeth with and without corticotomy were constructed. Brackets (size 0.022?inch?×?0.028?inch) were placed passively on all anterior teeth that were set at the centre of the labial surface in the mesio-distal dimension and 3?mm from the incisal edge to the bracket slot in the vertical direction. The power arm was set mesial of the canine bracket. For the model with corticotomy, the bone density was decreased from initial value at 5% to 25%. The point of force application was varied in order to locate the centre of resistance. The centre of resistance was located by measurement of the difference of the displacement between the apical and incisal edges. The position of force was varied by moving apically parallel to the occlusal plane to simulate tooth movement.

Results: As the alveolar bone density decreased from initial value to 25%, the location of the centre of resistance moved apically from the bracket slot from 10.8?mm to 11.2?mm, respectively.

Conclusions: The change of alveolar bone density due to corticotomy was associated with the location of the centre of resistance. The location of the centre of resistance moved apically as the alveolar bone density decreased but it was not clinically noticeable.