Comparison between landmark and surface-based three-dimensional analyses of facial asymmetry in adults

To collect the reference values for facial asymmetry in adults using landmark and surface-based three-dimensional analyses and to compare their diagnostic abilities. Laser scans were taken from 85 British Caucasians, 29 males (23.9±5.7 years, range 19-44) and 56 females (28.1±9.5 years, range 19-54), students and staff of the Cardiff Dental Hospital, and three orthodontic patients with marked facial asymmetry. An asymmetry index (AI) was measured for 14 landmarks. The surface-to-surface average distance between the best-fit registered original and mirror scans (ADom) was measured for the whole face and six regions. Non-parametric descriptive statistics was used to obtain the reference values, and Mann-Whitney U-test was used for gender comparison. P values less than 0.05 were considered significant. Patients' values were compared to the reference values by calculating the corresponding percentiles. The lowest AI was found for 'pronasale' in males [median 0.1 (interquartile range 0.0-0.3) mm] and the highest for 'cheilion' [3.5 (2.4-5.0) mm] in females. The ADom for the whole face was 0.7 (0.5-0.9) mm in males and 0.6 (0.5-0.7) mm in females and regionally between 0.4 (0.3-0.6) mm and 0.8 (0.4-1.2) mm. In orthodontic patients, AI did not always reveal asymmetry in a particular coordinate plane, and surface-based analysis was favourable in regions underrepresented by landmarks. Facial asymmetry can be accurately quantified using landmark- and surface-based approaches. The latter offers a more comprehensive analysis of the face.