Validity of identification of gonion and antegonion in frontal cephalograms

This study was designed to develop a method of transferring gonion from lateral to frontal cephalograms, and to use this method as gold standard when evaluating observer performance in identifying gonion in frontal cephalograms. Observer ability to identify antegonion was also evaluated. There was a range of 28 mm in the observers' identification of gonion and a statistically significant deviation from gold standard. The factors "observer" and "cephalogram," regarded as random effects in an ANOVA analysis, and their interaction, each influenced the result, P < .001. The deviation from the mean of all observations for antegonion ranged 8 mm with "cephalogram" having a statistically significant influence. The results suggest that neither gonion nor antegonion can be routinely used as valid landmarks in frontal cephalograms. Gonion can, however, be used if first identified in a lateral cephalogram and transferred to a paired frontal cephalogram aided by radiographic indicators combined with a bilateral scrutiny of projection geometry in different planes through gonion and indicator.