Objective  To investigate the centre of resistance of the maxillary anterior teeth and the accompanied initial displacement of teeth in en masse retraction with micro-implant anchorage.   Methods  A dry skull was scanned with high resolution spiral CT

and the obtained data were used to construct the three dimensional finite element model of “the micro-implant-segmented maxillary anterior teeth en masse retraction” force system. A 2 N horizontal retraction force by micro-implant were added to segmented maxillary teeth in every 2-mm interval from the archwire level and the initial displacement were calculated.   Results  The centre of resistance was located in the position of 5.1 mm above alveolar ridge. The centre of rotation constants were different among the central incisor

lateral incisor and canine.   Conclusion   The bodily movement or tipping movement can be easily achieved by altering the horizontal height of the retraction force using the “micro-implant-segmented maxillary anterior teeth en masse retraction” force system.