Les erreurs de mesure en céphalométrie 2D

The objective of this study is to analyze the influence that two parameters, thesource-subject distance and the type of receptor, have on the precision of localization ofthe 19 most frequently employed cephalometric landmark points and then to analyze therepercussions of localization errors on cephalometric measurements. The correct use ofprofile cephalograms (norma lateralis) for clinical purposes depends essentially on theprecision of the identification and localization of the different landmark points that arerequired for the elaboration of the various cephalometric analyses. For this study weasked 53 orthodontists, selected at random, to identify 19 cephalometric points onstandard profile or digitized films taken at distances of 1 m 50 or of 4 m. The results weobtained show no statistically significant differences in relation to the source-subjectdistance or to the type of receptor. Each cephalometric landmark presented acharacteristic dispersion cloud; the most reliable points were primarily located on themedian sagittal plane. The cephalometric measurements that demonstrated the greatestvariability were associated with positions of the incisor apices, which makes their valuedoubtful in the establishment of treatment plans and in ongoing evaluations of treatmentprogress. For similar reasons, the worth of the Frankfort plane can be questioned when itis compared to other, much more reliable cranial reference planes especially S-Na.