A Comparison of the apparent landmark changes in sequential radiographs measured by four methods of cephalometric superimposition

Abstract

Changes in growing individuals are evaluated by comparing tracings of cephalometric radiographs taken at different times. The methods of cephalometric superimposition differ according to the planes or anatomic structures used as references. It is not presently known if the superimposition method used has . any effect on growth interpretation and evaluation of orthodontic therapy. This study compa~ed four different methods of cephalometric superimpositions on the cranial base by investigating the differences in landmarks changes between methods. Tracings of pretreatment and posttreatment cephalograms of 30 patients were superimposed according to the following methods: 1-Sella-Nasion @ Sella, 2-Frankfort horizontal @ Ptv, 3- Basion-Nasion @ CC, and 4-Basion horizontal @ Basion. Differences in the amount of changes among the superimposition methods · were assessed independently for the following landmarks: ANS, PNS, A point, B point,· Pogonion, and Gonion. The results revealed statistically significant differences (ps0.05) among the methods for four out of the six landmarks studied. For the landmark ANS, there was a significant difference between FH @ Ptv and the rest of the methods. FH @ Ptv was also significantly different then SN @ S for point A with no difference among the three remaining techniques. For points Pogonion and Gonion, there \Vas a significant difference between FH @ Ptv and BN @ CC. Furthermore, there was a significant difference between FH @ Ptv and BN @ CC for point Gonion. These results show small but statistically significant differences among the methods of superimposition. This suggests caution in interpreting the longitudinal information from each method by a 9ommon set of guidelines. The clinical significance of the small differences ( ~ 1.2 · mm ) in the methods is a topic for future research.