Variance of landmarks in digital evaluations: comparison between CT-based and conventional digital lateral cephalometric radiographs.

AIM: The aim of this study was to examine whether bony, dental and soft tissue landmarks could be placed in CT-based lateral cephalograms with the same precision as in conventional digital lateral cephalograms.
MATERIALS AND METHODS: Nine patients without craniofacial dysplasia (2 female, 7 male, aged 12.8-32.3) who had undergone a lateral cephalogram and CT examination within an interval of a maximum of 6.5 months were selected in retrospect. The lateral cephalograms were done with the ORTHOPHOS Plus DS Ceph, and the CT examination with the SOMATOM Sensation 16 or 64 scanner. The CT-based cephalograms were generated with the VoXim 4.3 program based on axial CT reconstructions in the bone window. The cephalograms were analyzed using the Onyx Ceph 2.7 software by 2 orthodontists and 5 postgraduate students, each cephalogram being examined five times by each examiner on different days. Statistics were compiled with SPSS 13.0 and 14.0 based on the deviation from the individual mean value of each landmark.
RESULTS: The descriptive statistics showed in the conventional cephalogram, averaged over all 61 landmarks, a mean quartile range of on average 0.62 mm in the horizontal and 0.67 mm in the vertical axes. The CT-based cephalograms ranged between 0.64 mm horizontally and 0.74 mm vertically. The statistics comparing the two types of images with the Wilcoxon test for paired samples showed no significant difference.
CONCLUSION: When a CT scan is necessary for assessment of complex craniofacial dysplasias, an orthodontic-specific diagnosis is possible without having to resort to conventional X-rays of the skull. The data from this study demonstrate that it is possible to construct a cephalogram from CT data, which can be analyzed in the same way as a conventional cephalogram provided that the CT's field of view is large enough.