After a discussion in our Journal Club of a recent article (Sandler J, Murray A, Thiruvenkatachari B, Gutierrez R, Speight P, O’Brien K. Effectiveness of 3 methods of anchorage reinforcement for maximum anchorage in adolescents: a 3-arm multicenter randomized clinical trial. Am J Orthod Dentofacial Orthop 2014;146:10-20), we have some questions.
The sample size calculation of the study was based on a previous study that used a standard deviation of 1.8 mm for net molar movement relative to basal bone. In the current study, the largest standard deviation was 2.09 mm for the maxillary left molar movement in the headgear group. Since the standard deviation was larger than that in the original sample size calculation, did the authors consider a post hoc sample size calculation to determine whether the sample size was still appropriate?
Regarding the area for maxillary superimposition, the authors selected “the blue mushroom-shaped area based on the palatal rugae and a stable area of the hard palate.” However, according to a previous study, the most stable structure in the maxilla is “the medial 2/3 of the third rugae and the regional palatal vault dorsal to it.” This difference could have had a major impact on the superimposition and subsequent measurement of molar movement. What was the justification of choosing this region?
The authors used “the Euclidean distances between corresponding points on the 3D digital models at DC1 and DC2” for superimposition; however, those points are not “corresponding points” but “nearest points.” This could have biased the distance between the meshes during superimposition and could have produced an erroneous color distance map.
The authors carried out an error study at 2 time points (T1 and T2), the outcome measures of which were not adequately described. The difference in Euclidian distances of the “center of mass” or the centroid of the molar or the surface mesh points between T1 and T2 will only indicate the magnitude of the error but not the direction. In other words, after superimposition, the Euclidian distance between the points could be the same but in a different direction. The magnitude of the error should also have been reported.
The authors chose dental outcome measures in the main study but used SNA as baseline data. Even though the peer assessment rating score was used, pretreatment overjet, incisal angulation, and crowding are possible points to be considered in baseline data because these have a greater determination of anchorage requirements.