We want to thank Manni et al for their article in the June 2016 issue evaluating the effectiveness of the treatment of skeletal Class II malocclusions with an acrylic splint Herbst appliance anchored to miniscrews with 2 types of ligation (Manni A, Mutinelli S, Pasini M, Mazzotta L, Cozzani M. Herbst appliance anchored to miniscrews with 2 types of ligation: effectiveness in skeletal Class II treatment. Am J Orthod Dentofacial Orthop 2016;149:871-80). However, a few questions arose regarding the study design.

It was designed as a retrospective study, which could not avoid the confounding bias. The authors said that they chose subjects retrospectively by pairing the data to create groups homogeneous for age. Patients were selected also to balance the distribution of the sexes among the groups. However, the baseline information is not homogeneous in 3 groups. There were significant differences among 3 groups in overjet and mandibular incisor proclination; these might decrease the scientific value of this study.

Also, we do not know what specific criteria were used for dividing patients. From the study, we know that the criteria were the same, but why didn’t the authors randomly divide the patients into 3 groups? As we all know, randomized controlled trials provide the highest evidence and could prevent many biases.

Since the results of this study are very promising, we would appreciate it if the authors could share their views.