UCLA

Objectives: The establishment of a true 3-dimensional (3D) skeletal analysis of cone beam computed tomography (CBCT) images for orthodontic diagnoses has been a challenging endeavor, as previously proposed 3D analyses still rely upon 2-dimensional (2D) linear and angular measurements. In previous studies, the UCLA Section of Orthodontics, in a collaborative effort with the Laboratory of Neuro Imaging (LONI), developed a method for surface mapping a skull in three dimensions and expressing the curved outline of the structure using geometric algebraic methods. The long-term objective of the study is to establish a true three-dimensional (3D) skeletal analysis involving quantifiable 3D subnorms with respect to age, gender, and ethnicity. The specific aim of this study is to create a quantifiable 3D Korean adult normative skull that allows superimposition and comparison.

Materials and Methods: Quantifying samples followed the inclusion criteria of Korean adult male/female of ages greater than 18 and skeletal class I relationship based on cephalometric analyses. Patients with craniofacial defects, significant skeletal asymmetry, and/or previous history of orthodontic treatment were excluded. Using 11 male and 13 female normative CBCT images, the surface map and curved outline of each skull were generated by projective mapping and harmonic interpolation, and acquisition of points along the surface, respectively. The Procrustes superimposition method was used for normalization of samples.

Results: This normalized form provided a foundation for the comparison of an individual to the average, allowing sample differences to be visualized and quantified. The establishment of a linear distance map, directional vector map, and statistical map effectively showed clear deviation of individual skulls to the norm.

Conclusion: The establishment of subnorms is a difficult task due to limited sample size from stringent inclusion and exclusion criteria, but can be successfully done utilizing the methods we developed. Further studies accounting for ethnicity, gender, and age will strengthen the diagnostic power of CBCT images in orthodontics.