Philipp Berssenbrügge

Quantification of facial asymmetry by 2D analysis – A comparison of recent approaches

INTRODUCTION Symmetry has been found to play a crucial role in attractiveness assessment and so its restoration is an essential problem in oral maxillofacial surgery. This paper presents an overview of recent 2D asymmetry analysis techniques. These are techniques which are based on the evaluation of two-dimensional data, like photos. The aim of this paper is to find the most precise and practical techniques to investigate facial asymmetry. MATERIALS AND METHODS For this purpose studies addressing symmetry investigations are collected and categorized by the type of data they extract from the photos. The reference points on the facial surface, which are frequently used in these studies, are presented and calculation methods are described. RESULTS Three kinds of techniques using vertical or horizontal reference lines or centres of bilateral points appear to be most appropriate. Recommendations are made, which aspects should be taken into account when calculating symmetry/asymmetry indices from photos. Advantages and disadvantages of the three selected methods are summarized in a table. CONCLUSIONS Using one of the three recommended approaches denoted by FA, AI and z-score allows calculating meaningful asymmetry values. The proper selection and identification of reference points is crucial. For highest accuracy, a sufficient number of evenly distributed and reproducible reference points should be used.

Measured symmetry of facial 3D shape and perceived facial symmetry and attractiveness before and after orthognathic surgery.

One aim of cranio-maxillo-facial surgery is to strive for an esthetical appearance. Do facial symmetry and attractiveness correlate? How are they affected by surgery? Within this study faces of patients with orthognathic surgery were captured and analyzed regarding their symmetry. A total of 25 faces of patients were measured three-dimensionally by an optical sensor using the fringe projection technique before and after orthognathic surgery. Based upon this data an asymmetry index was calculated for each case. In order to gather subjective ratings each face was presented to 100 independent test subjects in a 3D rotation sequence. Those were asked to rate the symmetry and the attractiveness of the faces. It was analyzed to what extend the ratings correlate with the measured asymmetry indices and whether pre- and post-surgical data differ. The measured asymmetry indices correlate significantly with the subjective ratings of both items. The measured symmetry as well as the rated symmetry and attractiveness increased on average after surgery. The increase of the ratings was even statistically significant. A larger enhancement of symmetry is achieved in pre-surgical strongly asymmetric faces than in rather symmetric faces.

Simultaneous acquisition of 3D shape and deformation by combination of interferometric and correlation-based laser speckle metrology

A metrology system combining three laser speckle measurement techniques for simultaneous determination of 3D shape and micro- and macroscopic deformations is presented. While microscopic deformations are determined by a combination of Digital Holographic Interferometry (DHI) and Digital Speckle Photography (DSP), macroscopic 3D shape, position and deformation are retrieved by photogrammetry based on digital image correlation of a projected laser speckle pattern. The photogrammetrically obtained data extend the measurement range of the DHI-DSP system and also increase the accuracy of the calculation of the sensitivity vector. Furthermore, a precise assignment of microscopic displacements to the objects macroscopic shape for enhanced visualization is achieved. The approach allows for fast measurements with a simple setup. Key parameters of the system are optimized, and its precision and measurement range are demonstrated. As application examples, the deformation of a mandible model and the shrinkage of dental impression material are measured.

Measuring facial symmetry: a perception-based approach using 3D shape and color

Abstract Objective: Facial symmetry is an important factor affecting esthetics. Thus, its restoration is an essential task in maxillofacial surgery. The aim of this study is to develop an objective measure of facial asymmetry by a novel approach where both the shape and the color are taken into account and to validate its correlation with perception. Methods: Optical three-dimensional (3D) face scans of 30 healthy adults are performed. Face-specific asymmetry indices are calculated by quantifying color differences as well as spatial distances between 3D data of a face and its mirrored copy. Subjective ratings of symmetry and attractiveness of the faces by 100 subjects are used to validate these indices. Results: The symmetry ratings show significant correlations with color and geometric asymmetry indices. The attractiveness ratings correlate only weakly with both indices. However, the product of the indices exhibits significant correlations with both attractiveness and symmetry ratings. Conclusion: The presented combined asymmetry index comprising shape and coloring turned out to reflect subjective perception of both facial symmetry and attractiveness. It thus promises to be a valid objective measure for facial esthetics, which could contribute, e.g., to the evaluation of surgical methods as well as to the design of craniofacial prostheses.