I read with interest the recent article entitled “Herbst appliance anchored to miniscrews with 2 types of ligation: Effectiveness in skeletal Class II treatment” (Manni A, Mutinelli S, Pasini M, Mazzotta L, Cozzani M. Am J Orthod Dentofacial Orthop 2016;149:871-80).
Although the study was retrospective, it is understood that the authors showed great efforts to eliminate the disadvantages of a retrospectively designed clinical study. The sample size was determined using a sample calculation method before the study began, and the groups were well matched according to age and sex distributions. However, I have some questions and suggestions.
The method used to determine the sample size should have been described completely. Whose sample calculation method was used? (I can suggest the method of Dr Pandis, who is an associate editor of the AJO-DO. ) In addition, the mean difference for pogonion advancement among the groups stated in the text (2.0 ± 2.0 mm) seems not to be based on the study findings they cited, because I also read the other study. It might have been better to use findings from a previous study.
It is known that the occlusal plane is affected by functional fixed appliances, and thus this change might have affected their findings if the clinicians had used this plane as a vertical reference line. I suggest that the authors should use a vertical reference line that is not affected by both treatment and growth to understand the pure effects of the appliances.
Finally, how did the authors orient the degree of the force as 100 g in the metallic ligature Herbst group?