We would like to thank Dr Yongwen Guo for his questions about our article, since this allows us to clarify certain points and prevents misunderstandings and wrong interpretations of the purpose and findings of the study.

Concerning the first point, we agree that the indications for premolar extractions are more than severe crowding. Therefore, situations with moderate crowding in patients with dental protrusion were considered to be severe crowding, since no option other than premolar extractions could be the treatment of choice. This was the case for the patient shown in Figure 1 for whom tooth crowding in the maxillary and mandibular arches demanded 4 premolar extractions.

Regarding the second point, an intra-arch obstacle to the movement of the experimental teeth was independent of the amount of the crowding in the arch. For example, patients with the same degree of crowding could have (1) nicely aligned premolars without an intra-arch obstacle with localized crowding in the anterior region and (2) premolars with irregular positions and intra-arch obstacles by the adjacent teeth. Therefore, we did not attempt to relate our experimental tooth movements with the general space conditions in the arch; rather, we preferred to indicate whether the experimental teeth could move freely during the experimental period. As far as we know, our study was the first to focus on this aspect, indicating the importance of intra-arch obstacles in this type of tooth movement. Therefore, our findings suggest that in future studies, the degree of severity of intra-arch obstacles that might be independent of the general space conditions of the arch could be useful information to further understand the importance of this factor.

We agree with Dr Guo that there might be an additive impeding effect on tooth movement when intra-arch and interarch obstacles are simultaneously present. However, in our study, as shown in the “Results,” both factors were not simultaneously present, so this did not allow this kind of evaluation.

Last but not least, we want to stress that our study focused on factors influencing this kind of experimental tooth movement and does not provide evidence to support Dr Guo’s suggestion that “It might be advisable to extract the premolars early in patients with severe crowding and interarch obstacles to tooth movement if they are scheduled for premolar extractions.”