We thank Dr Pingkuai Yang for these 2 questions about our study design.
The first point is about selection bias and confounding for heterogeneity in overjet amount and mandibular incisor position at baseline in the 3 groups.
In our research, the main inclusion criterion for the sample was the clinical request of advancing the mandible to improve chin projection. As a consequence of this, the treatment goal was pogonion advancement. Malocclusion severity was therefore defined by clinically evaluating chin position and cephalometrically measuring distance from pogonion to occlusal line perpendicular. This distance was pretty close among the groups, and they were actually homogeneous. The severity of skeletal class must not be defined on the basis of dental measurements such as overjet and mandibular incisor position.
Therefore, selection bias wasn’t present. It must be clear that the patients were enrolled by evaluating chin position and not overjet and mandibular incisor inclination. The amount of overjet or mandibular incisor proclination did not influence the probability for a patient to be included in the study. Finally, the differences at baseline in mandibular incisor position and overjet didn’t bias patient selection.
Regarding baseline overjet and incisor proclination as confounders, to our knowledge, no data are available in the literature to define incisor position and amount of overjet as risk factors for skeletal correction of Class II and specifically for Herbst treatment effect (outcome, pogonion advancement).
Consequently in our study design, they can’t be defined as confounders.
It is only known that mandibular incisor flaring can be a negative side effect; therefore, the use of skeletal anchorage can be beneficial.
Moreover, it is clinical experience, but there is no scientific evidence, that mandibular incisor proclination can be an obstacle for mandibular advancement in this type of malocclusion because it reduces the overjet itself. It is not important what is the baseline position of the mandibular incisors, but rather how much they procline during treatment. This is why skeletal anchorage could be beneficial, and we have considered it as an exposure to take into account. In the same way, it could be hypothesized that a greater overjet favors mandibular advancement. However, our results showed that patients with the narrowest overjet had the best response to treatment.
Regarding the “specific criteria for dividing patients” used in our research, it is difficult to see the connection between this question and the design of our study. In fact, our study was a retrospective observational study (case-control), where we analyzed the effect of a treatment on a cohort of patients. On the contrary, a case report or a case series is a detailed description of unexpected and unusual symptoms, diseases, treatments, and outcomes of individual patients. Then, it is well known that researchers in observational studies are passive and observe the effects of treatment without choosing the type of treatment for each patient (randomization). Lastly, we agree that a randomized controlled trial is the best study design, but observational studies can also help us to understand daily clinical conditions and treatment effects.