We want to thank Dr Khambay for his interest in our study. We will answer his observations in the order they were presented.
We did not consider a post hoc sample size calculation because this cannot be used to address whether an observed nonsignificant effect reflects the absence of a population effect or a lack of power. Once the effect of a study is known, however, the degree of uncertainty can be evaluated from 95% confidence intervals. Examination of our data shows that any differences between the groups were small, with 95% confidence intervals that were small.
We have noted the comments on the evaluation of error and molar movement. We did report that the error was small. We also want to point out that the models were analyzed blindly; therefore, any measurement error would apply equally to the intervention groups, and this would not have influenced the findings of our trial.
SNA was only used to demonstrate pretreatment equivalence. When we designed the study, we decided that it should be as close to the “real world” of clinical practice as possible. We therefore used a broad clinical definition of maximum anchorage, based on a clinical assessment by the operator. Of course, pretreatment overjet, incisal angulation, and crowding have a bearing on anchorage requirements but, because all patients needed “absolute anchorage,” the magnitude of these other factors had no relevance to this study.