At intrusion of upper anterior teeth in patient with periodontal defect, the use of three-piece base arch appliance for pure intrusion is required To investigate the change of the center of resistance and of the distal traction force according to alveolar bone height at intrusion of upper anterior teeth using this appliance, three-dimensional finite element models of upper six anterior teeth, periodontal ligament and alveolar bone were constructed.
At intrusion of upper anterior teeth by three-piece base arch appliance, the following conclusions were drawn to the locations of the center of resistance according to the number of teeth, the change of distal traction force for pure intrusion and the correlation to the change of vertical, horizontal location of the center of resistance according to alveolar bone loss.
1. When the axial inclination and alveolar bone height were normal, the anteroposterior locations of center of resistance of upper anterior teeth according to the number of teeth contained were as follows 1) In 2 aiterior teeth group, the center of resistance was located in the mesial 1/3 area of lateral incisor bracket. 2) In 4 ai terror teeth group, the center of resistance was located in the distal 2/3 of the distance between the bracket
of lateral incisor and canine.
3) In 6 anterior teeth group, the center of resistance was located in the central area of first premolar bracket.
4) As the number of teeth contained in anterior teeth group increased, the center of resistance shifted to the distal side.
2. When the alveolar bone height was normal, the anteroposterior position of the point of application of the intrusive force was the same position or a bit forward position of the center of resistance at application of distal traction force for pure intrusion.
3. When intrusion force and the point of application of the intrusive force were fixed, the changes of distal traction force for pure intrusion according to alveolar bon loss were as follows
1) Regardless of the alveolar bone loss, the distal traction force of 2, 4 anterior teeth groups were lower than that of 6 anterior teeth group.
2) As the alveolar bone loss increased, the distal traction forces of each teeth group were increased.
4. The correlation of the vertical, horizontal locations of the center of resistance according to maxillary anterior teeth groups and the alveolar bone height were as follows
1) In 2 anterior teeth group, the horizontal position displacement to the vertical position displacement of the center of resistance according to the alveolar bone loss was the largest.
As the number of teeth increased, the horizontal position displacement to the vertical position displacement of the
center of resistance according to the alveolar bone loss showed a tendency to decrease.
2) As the alveolar bone loss increased, the horizontal position displacement to the vertical position displacement of the
center of resistance regardless of the number of teeth was increased.
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