Gautham Sivamurthy^1,, Shantha Sundari²

Cephalometrics still remains imperative in diagnosis and therapeutic decision making and with the realisation of the natural head posture, the Frankfort horizontal (FH) plane cannot be considered a true horizontal in all cases due to its commonly deviant relationship, particularly in cases of vertical skeletal discrepancies. The purpose of this study was to highlight the erroneous reflections of maxillary and mandibular positions in cases where the FH plane is deviant from the normal and to construct an alternate reference plane for use in such situations. The sample group came from 55 randomly selected lateral cephalometric roentgenograms. A control group of 20 patients was created from the cephalograms where the FH plane was in a true horizontal relationship and an alternate study reference plane was constructed. An independent t test and Mann-Whitney U test were done for both the groups to compare the values obtained and determine the statistical difference. In the control group, the values obtained where statistically not significant, which proved that our reference plane could be used as an alternative to the FH plane. The study group showed a significant statistical difference, resulting in erroneous analysis if the deviant FH plane was used. Gross errors in diagnosis and treatment planning of orthodontic and surgical cases can occur if deviant FH plane is used in cephalometric analysis.

frankfort horizontal plane, true horizontal, natural head posture, vertical skeletal discrepancy, devian, reference plane