Comparison of different calculation methods used to analyze facial soft tissue asymmetry: Global and partial 3D quantitative evaluation of healthy subjects

Publication date: Available online 20 May 2016
Source:Journal of Oral and Maxillofacial Surgery
Author(s): U. Ozsoy
PurposeAn accurate assessment of range and localization of facial asymmetry is essential to restore facial symmetry. Establishment of a common and well accepted calculation method may facilitate the interpretation of the assessments results. The aim of the present study was to analyze global and partial asymmetry of facial soft tissues with three different calculation methods and to investigate relationships among them.MethodsFacial asymmetry was performed on the 3D images of 51 subjects (23 males: mean, 22 ± 2.2 years; 28 females: mean, 21.1 ± 2.1 years) acquired by a 3D hand held scanner. A mirror image of a facial mask was generated and superimposed on the original mask. Afterwards, root mean square (RMS), mean absolute deviation (MAD) and mean signed distance (MSD) values were calculated between original and mirror images.ResultsThe calculated difference between the total facial masks (amount of asymmetry) was 0.95±0.29mm with RMS, 0.72±0.22mm with MAD and -0.04±0.05mm with MSD. A very high correlation was found between RMS and MAD (r=0.98). On the contrary, the correlation between MSD and RMS (r=-0.26) or MAD (r=-0.25) were poor. The CV value of MSD (133%) was significantly higher than RMS (30%) and MAD (30%) (p<0.05)ConclusionOn the basis of these results, we conclude that both RMS and MAD are accurate and reliable methods in a facial asymmetry assessment. However, MSD is insufficient alone but can be used as a side parameter showing the direction of the asymmetry.



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