The Accuracy of Conformation of a Generic Surface Mesh for the Analysis of Facial Soft Tissue Changes.
OBJECTIVE
Three dimensional analysis of the face is required for the assessment of complex changes following surgery, pathological conditions and to monitor facial growth. The most suitable method may be "dense surface correspondence".


METHODS
This method utilizes a generic facial mesh and "conformation process" to establish anatomical correspondences between two facial images. The aim of this study was to validate the use of conformed meshes to measure simulated maxillary and mandibular surgical movements. The "simulation" was performed by deforming the actual soft tissues of the participant during image acquisition. The study was conducted on 20 volunteers and used 77 facial landmarks pre-marked over six anatomical regions; left cheek, right cheek, left upper lip, philtrum, right upper lip and chin region. Each volunteer was imaged at rest and after performing 5 different simulated surgical procedures using 3D stereophotogrammetry. The simulated surgical movement was determined by measuring the Euclidean distances and the mean absolute x, y and z distances of the landmarks making up the six regions following digitization. A generic mesh was then conformed to each of the aligned six facial 3D images. The same six regions were selected on the aligned conformed simulated meshes and the surgical movement determined by determining the Euclidean distances and the mean absolute x, y and z distances of the mesh points making up the six regions were determined.


RESULTS
In all cases the mean Euclidian distance between the simulated movement and conformed region was less than 0.7 mm. For the x, y and z directions the majority of differences in the mean absolute distances were less than 1.0mm except in the x-direction for the left and right cheek regions, which was above 2.0 mm.


CONCLUSIONS
This concludes that the conformation process has an acceptable level of accuracy and is a valid method of measuring facial change between two images i.e. pre- and post-surgery. The conformation accuracy is higher toward the center of the face than the peripheral regions.
Faculty of Dentistry, University of Hong Kong, Hong Kong, China.
Man Yan
MY
Cheung
Glasgow Dental School, University of Glasgow, Glasgow, United Kingdom.
Anas
A
Almukhtar
School of Dentistry, University of Leeds, Leeds, United Kingdom.
Andrew
A
Keeling
Faculty of Dentistry, University of Hong Kong, Hong Kong, China.
Tai-Chiu
TC
Hsung
Glasgow Dental School, University of Glasgow, Glasgow, United Kingdom.
Xiangyang
X
Ju
Glasgow Dental School, University of Glasgow, Glasgow, United Kingdom.
James
J
McDonald
Glasgow Dental School, University of Glasgow, Glasgow, United Kingdom.
Ashraf
A
Ayoub
Faculty of Dentistry, University of Hong Kong, Hong Kong, China.|School of Dentistry, University of Leeds, Leeds, United Kingdom.
Balvinder Singh
BS
Khambay
D059925:Anatomic Landmarks / Q000502:physiology; D054893:Cone-Beam Computed Tomography / Q000379:methods; D003238:Connective Tissue / Q000502:physiology*; D005145:Face / Q000033:anatomy & histology* / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008334:Mandible / Q000033:anatomy & histology / Q000502:physiology; D008437:Maxilla / Q000033:anatomy & histology / Q000502:physiology; D010780:Photogrammetry / Q000379:methods