Comparison of Mandibular Landmarks from Computed Tomography and 3D Digitizer Data

We recorded 3D coordinates for 28 mandibular landmarks from three-dimensional reconstructions of CT axial slices using the image analysis program eTDIPS. The images were acquired from a pediatric series of human mandibles (neonate to 13 years of age) from the Bosma collection (Shapiro and Richtsmeier, 1997, Am. J. Phys. Anthropol. 103:415-416). To test the accuracy of these coordinate data, we recorded the same 28 landmarks directly on the Bosma mandibles using a Polhemus 3Space digitizer. The directly digitized landmarks serve as a gold standard upon which to evaluate the eTDIPS data. Standard deviations of landmark placement using eTDIPS show a greater degree of variation compared to the data gathered using the digitizer, although this error is more heavily concentrated in certain types of landmarks. All possible linear distances between unique pairs of landmarks were calculated, and like linear distances were compared between the two data collection methods. The absolute difference for all like linear distances ranged from 0.001-3.9 mm (mean = 0.377 mm; SD = 1.136), with the eTDIPS data being consistently larger than the digitizer coordinates. This study demonstrates that landmark coordinate data can be reliably collected from digital CT images of the human mandible. We define a set of mandibular landmarks useful in evaluating the effects of craniofacial disorders, growth and other biological processes.