EFFECTS OF CEPHALOMETRIC LANDMARK VALIDITY ON INCISOR ANGULATION

An experimental cephalometric study on the accuracy of independently locating eight landmarks and the subsequent effects on the maxillary (ILs/NL) and mandibular (ILi/ML) incisor angulation was carried out on 30 dry skulls. The true location of each landmark was marked with a steel ball glued onto the skulls. Two additional steel balls were used as reference markers. A purpose-designed skullholder was made to assure a firm and reproducible positioning of the skulls in the cephalostat. Six series of cephalograms were recorded. One reference series with all the steel balls, four series each with a single steel ball marker removed, one at a time, from each jaw and one series with all the steel ball markers removed, except the reference markers. The combined method error in relocating and replacing the steel ball markers, repositioning the skulls into the skull holder, and digitizing, was low. From the first series, the true position of the palatal plane (NL), the maxillary incisor line (ILs), the mandibular plane (ML) and the mandibular incisor line (ILi) were assessed. From series 2 to 5, each of the landmarks without the steel ball markers was estimated. The accuracy of each landmark was then assessed relative to the true cephalometric plane and its perpendicular. On average, the accuracy was high for all the landmarks except posterior nasal spine (PNS), which was estimated 1.2 mm too far anteriorly (p < 0.05). The standard deviations of the accuracy of the dental and skeletal landmarks were similar, being 1.4 to 2.4 mm. The maxillary incisors were proclined 1.1 degrees (p < 0.05) by the estimates of incision superior (Is). The mandibular incisors were retroclined 0.3 degrees (p < 0.05) by gonion, 1.0 degrees (p < 0.01) by menton, and 1.1 degrees (p < 0.05) by apex inferior. The standard deviations of the incisor angulations were low (0.6 degrees) both for ANS and gonion, moderate for PNS (1.3 degrees) and menton (1.0 degrees), and high for the dental landmarks (1.8 degrees to 2.8 degrees).