Identification of the Palatal Plane in Cephalometrics

Objectives: Accurate analysis of a lateral cephalogram for orthodontic purposes requires, amongst other parameters, selection of the most appropriate reference line. The Frankfort horizontal (FH) is frequently used. Since four clinicians from the Orthodontic Department of the University of Pretoria were able to identify FH in only 42 out of 94 cephalograms, it was decided to test the identifiability of the palatal plane (PP) which some authors consider a reliable alternative to FH. PP is constructed by joining the anterior and posterior nasal spines (ANS) to (PNS). Method: The 94 lateral cephalograms used for the study of FH were viewed by the same four clinicians on a light box in a darkened room without magnification. The clarity of the landmarks ANS and PNS were identified on an arbitrary scale of 1 – 100. PPs were only considered acceptable when at least three clinicians could positively identify both these landmarks at a 75% level. Results: At best only 22 cephalograms showed identifiable PPs, significantly less than the 70 required for a 75% success rate.Statistical analysis,however,showed the inter-observer error to be highly significant in all cases. Conclusion: The use of PP as an alternative to FH may yet be valid.A further study is necessary due to lack of agreement as to the positive identification of the landmarks.