Objective: Prediction and planning of the orthodontic tooth movement have mostly depended on clinical experiences. If the initial tooth displacement measured in vivo could be a predictor of tooth movement after a long-term process of bone remodeling, treatment results will be greatly improved. The purpose of the present study was to verify the validity of an assumption that initial tooth displacement can be a predictor of orthodontic tooth movement.

Methods: The subjects consisted of adult patients with maxillary protrusion who were undergoing orthodontic treatment. Prior to retraction of anterior teeth using sliding mechanics, initial tooth displacement was measured in three dimensions in vivo by means of a magnetic sensing system. After the retraction was completed, 3D images of dental cast profiles before and after retraction were obtained using a laser scanning system (VMS-150R-D, UNISN Inc, Osaka, Japan) and three-dimensional tooth movements were calculated. Then we compared the type of tooth movement obtained from a magnetic sensing system and laser scanning system.

Results: It was found that the type of tooth movement, namely, the location of center of rotation during orthodontic tooth movement was 2 mm incisal to that predicted in the light of in-vivo measurement of initial tooth displacement.

Conclusion: It was concluded that the tipping tendency can be slightly increased in the course of treatment due to the change of moment-to-force ratio modified by the uprighting of the anterior teeth. Although the prediction of orthodontic tooth movements is still difficult, consideration of the change in force system may enable the precise simulation of orthodontic tooth movement

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