Title: Defining Hard and Soft Tissue Asymmetry Using 3-dimensional CBCT Analysis
Marisa Reason (Presenter)
David Briss, Boston University
Objectives: The aim of the study is to establish appropriate, reproducible soft tissue landmarks and a bony counterpart in CBCT images, evaluate the correlation between the skeletal and soft-tissue landmarks, and use the measurement correlations to objectively define asymmetry to discover where asymmetries originate.
Methods: Pre-treatment Cone Beam Computed Tomography (CBCT) films of 160 esthetic human subjects previously used by another investigator were screened for use. The DICOM files were imported into InVivoDental5.3 software (AnatomageTM; San Jose, Calif.) for screening and 60 CBCT scans were selected for analysis. A soft tissue mask was created on all scanned images. 17 anatomic bony and soft tissue landmarks were identified in all three planes of space. The reference planes were defined as Nasion (x), Midpoint of Clinoid Processes (y), and the most inferior point of the inter-maxillary suture (z). Each landmark was given an (x,y,z) coordinate and bilateral linear measurements to the reference planes were recorded. Ratios were established between the soft tissue point and bony tissue counterpart in all three planes. InVivoDental5.3 software was used to calculate linear distances between each landmark and the reference planes. Descriptive statistics of our sample and correlation analyses were performed. The mean average and standard deviation of each landmark was calculated. Also the correlations between the respective hard and soft tissue landmarks were calculated.
Results: A comparison between the hard and soft tissue landmark means was accomplished with the use of paired t-tests. It was founded that hard and soft tissue landmarks do have positive correlations, but four landmarks existed which showed statistical difference in location relative to the reference planes (p<.0.05).
Conclusions: The trend of the data indicates a significant relationship between the soft and hard tissue points in CBCT images. The statistically significant skeletal and corresponding soft tissue landmarks, could be due to tracing error, given the indiscrete location of some of the landmarks. However, these results could lead further researchers to use this information to discover the reasons behind the location differences, and start to define where asymmetries initiate in the skeleton and overlying facial soft tissue.