Predictability of maxillary canine retraction comparing power arm and non-power arm using 24 sets of In-house clear aligner in premolar extraction case: a randomized controlled trial.

Background: The bowing effect observed during premolar extractions presents a challenge in clear aligner therapy. This study aims to investigate the accuracy of maxillary tooth movement in first premolar extraction cases using the in-house clear aligner (IHCA), comparing the palatal power arm (PA) and non-power arm (control / C).

Methods: Eighteen adults requiring maxillary first premolars extraction using IHCA were recruited. Using a randomized controlled trial with a split-mouth design, each patient received treatment for both PA and C. Data at the 24th IHCA comprising virtual-power arm (VPa), virtual-control (VC), actual-power arm (APa) and actual-control (AC) were measured by superimposition with pretreatment digital model, using 3D GOM Inspect software. Six types of tooth movement were assessed. Paired t-test or Wilcoxon signed-rank test was used to compare the differences between groups. Root mean square error (RMSE) as predictability was computed.

Results: For the maxillary canine, there was no significant difference between the PA and C groups for all types of tooth movement except rotation. Specifically, the PA exhibited a significantly less difference in distal-in rotation compared to the control group (APa-VPa -3.54°/AC-VC -11.57°). Similarly, the RMSE of PA demonstrated better accuracy in rotation than the control (PA 7.85°/control 15.98°). In terms of anchorage, the RMSE of PA indicated greater deviation than the control in the second premolar mesial-in rotation and crown-tipping. Regarding the first molar, the RMSE of PA was mostly similar to that of the control.

Conclusion: IHCA can effectively retract maxillary canines in cases involving premolar extraction. However, although palatal power arms improve the accuracy of canine rotation, no notable benefits are seen for other types of tooth movement or for anchorage control.

Trial registration: Current Controlled Trials ISRCTN14020146 of the International Standard Randomized Controlled Trial. The date of registration was 16/11/2022. The trial was retrospectively registered.