How accurate is predicted root movement achieved in four first-premolar extraction cases with Invisalign?

Objectives

This study aims to compare the achieved and predicted root movements in adults after four first-premolar extractions and Invisalign treatment.

Materials and Methods

Thirty-three consecutive adults (22 Class I, 9 Cusp-to-cusp Class II and 2 Cusp-to-cusp Class III) from a single clinical division who completed the first series of aligners after premolar extractions were included in this retrospective study. A pretreatment cone-beam computed tomography model was registered onto the pretreatment surface-scanned dental model (SSDM) to locate the pretreatment root apices of the whole dentition. These were copied and transferred to the predicted and achieved post-treatment SSDMs to acquire the locations of the predicted and achieved post-treatment root apices. The differences between predicted and achieved root movements (DPARMs) were tested using the paired t-test or Wilcoxon signed rank test.

Results

In the anteroposterior direction, posterior root movements of maxillary and mandibular anterior teeth were poorly achieved (3.24–5.74 mm DPARMs, p < .05). In the vertical direction, roots of maxillary anterior teeth achieved greater intrusion (0.70–0.93 mm DPARMs, p < .05), while those of mandibular incisors achieved less intrusion (0.57–0.65 mm DPARMs, p < .05) than predicted. In the mediolateral direction, lateral incisor roots did not move distally (−0.65 to −0.96 mm DPARMs, p < .05), while those of canines did not move buccally, compared with the prediction (−0.75 mm DPARMs, p < .05).

Conclusions

In the four first-premolar extraction treatments with Invisalign, root movements were not achieved as predicted, particularly for anterior teeth in the anteroposterior direction.