Evaluation of extraction and non-extraction treatment effects by two different superimposition methods

The aim of this study was to determine whether different evaluation methods may be the cause of the varied outcomes of research that have evaluated the effects of extraction and non-extraction therapy on jaw rotation. This retrospective study consisted of the pre- (T1) and post- (T2) treatment lateral cephalograms of 70 skeletal Class I subjects with an optimal vertical mandibular plane angle, who had undergone fixed orthodontic treatment. Thirty-five of the subjects (20 females and 15 males, mean age: 14.7 years) were treated with four first premolar extractions and 35 (22 females and 13 males, mean age: 15 years) without extractions. T1 and T2 radiographs were superimposed using Björk's structural method and Steiner's method of sella-nasion line registered at sella. A Wilcoxon test was used to evaluate the changes between T1 and T2 and the Mann-Whitney U-test to determine differences between the extraction and non-extraction and Björk and Steiner groups. No significant difference was found between the methods of Steiner and Björk according to the spatial changes of the cephalometric points in the extraction and non-extraction groups. The maxilla showed forward rotation in the extraction group and backward rotation in the non-extraction group with both superimposition methods, but the differences were not significant in either inter- or intraclass comparisons. The mandible showed forward rotation in the extraction group with both superimposition methods but, in the non-extraction group, forward rotation was recorded with Björk's method and backward rotation with Steiner's method. These findings were not significant in either inter- or intraclass evaluations. No significant difference was found between the groups or methods.