Validity of identification of gonion and antegonion in frontal cephalograms

This study was designed to develop a method of transferring gonion from lat eral to frontal cephalograms, and to use this method as gold standard when evaluating observer performance in identifying gonion in frontal cephalogra ms. Observer ability to identify antegonion was also evaluated. There was a range of 28 mm in the observers' identification of gonion and a statistica lly significant deviation from gold standard. The factors "observer" and "c ephalogram," regarded as random effects in an ANOVA analysis, and their int eraction, 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 goni on nor antegonion can be routinely used as valid landmarks in frontal cepha lograms. Gonion can, however, be used if first identified in a lateral ceph alogram and transferred to a paired frontal cephalogram aided by radiograph ic indicators combined with a bilateral scrutiny of projection geometry in different planes through gonion and indicator.