Relative position of porion and tragus in orthodontic patients.

In order to assess the relationship between the hard (porion-orbitale) and soft (tragus-orbitale) tissue Frankfurt planes, the relative positions of porion, orbitale, and tragus were evaluated on cephalometric radiographs. A 5-mm radiopaque disk was fixed on the right tragus of 160 white orthodontic patients (65 males aged 7 to 28 years, and 95 females aged 7 to 36 years), and a pre-treatment lateral cephalometric radiograph was taken. In every film the positions of orbitale, porion, and tragus were digitized, and the linear distances between the points, as well as the position of tragus relative to the skeletal structures, were calculated. The linear distances porion-orbitale and tragus-orbitale progressively increased with age, with a low variability in all age classes. The linear distances were always larger in the males than in the females. The tragus was always lower and more anterior than the porion, with vertical distances ranging from 1.2 to 19.8 mm. When the porion-tragus distance was expressed as a percentage of the porion-orbitale distance, the variability decreased. In the age classes, mean percentage horizontal projections from porion ranged from 18 to 23% of the porion-orbitale distance, mean percentage vertical projections ranged from 8 to 15%. Unfortunately, sample variability was large, and, in a single patient, the position of tragus relative to the skeletal structures could be predicted only with a large approximation.