To: The Editor, The Angle Orthodontist

Re: Response to: Efficiency of upper arch expansion with the Invisalign system. Ning Zhou; Jing Guo. Angle Orthod. 2020; 90: 23–30.

Thank you so much for your questions. We are elaborating on the design details based on your questions. We hope it will be helpful for you.

  1. The effect of molar rotation on arch width was considered in the whole treatment plan. But in order to achieve transverse translation of posterior teeth during the arch expansion, the molar rotation was not designed into the expansion procedure.

  2. Regarding the transverse amount of expansion prescribed for each patient: We were hoping to achieve bodily expansion instead of tipping movement through the expansion procedure. To that end, different degrees of reverse torque on posterior teeth were designed into the stage of arch expansion based on the initial torque of the teeth and the amount of expansion. Hence, the protocol was customized for all the participants in the study.