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A Novel Analysis of Skeletal Asymmetry Utilizing 3D CBCT Technology: The Ulrich Analysis


Introduction: Proper diagnosis and treatment planning is essential to the outcome of orthodontic therapy with accurate diagnostic records being the pinnacle of that process. Previously, two-dimensional imagery has been the standard in analyzing or visualizing a patient for skeletal asymmetries but has numerous limiting factors. The limitations that two dimensional analyses face can be solved by the use of three-dimensional cone beam computed tomography (CBCT) when combined with an efficient and relevant analysis. The purpose of this study was to design a novel analysis of asymmetry utilizing CBCT that could be used in a standard orthodontic diagnostic analysis.

Methods: CBCT images of 35 patients from the UCSF Orthodontic Clinic were used for development of the analysis. A pilot study with 5 patients having marked asymmetries was traced at 3 different time points to aid in landmark verification and assess reliability. A series of landmarks sharing commonalities with those used in two-dimensional cephalometric analysis were applied. A Pearson Correlation Coefficient with Bonferonni correction as well as a Bland-Altman test for reproducibility was applied for the three timepoints on five different patients to test intraobserver reliability. 10 patients with a molar Class I malocclusion, 10 patients with CII malocclusions, and 10 with CIII malocclusions were used to create a sample of patients with the applied orientation method and asymmetry analysis.

Results: Landmark identification was found to be reproducible with only a weak statistical difference in landmark identification. No statistically significant differences were found between any landmarks and their different timepoint selections, particularly those points essential to the establishment of the analysis axis (p<.05). The index provided a quantitative assessment in three planes for both numerical and visual evidence of asymmetry.

Conclusions: The Ulrich Orthodontic Asymmetry analysis, combined with reliable and reproducible landmark selection, allows for successful quantitative assessment of asymmetry identification in both 2-dimensional and 3-dimensional visualizations and may provide a standard diagnostic tool to be used with patients seeking orthodontic treatment.

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