Facial scanners provide three-dimensional topography of the facial surface anatomy, automatic facial landmark recognition, and analysis of the symmetry and proportions of the face. Practical applications further include quantitative and qualitative assessment of growth and development, ethnic variations, gender differences, and isolation of specific diagnostic traits in selected populations of patients with craniofacial anomalies [ 52 , 53 ]. In addition, facial phenotype associated with fetal alcohol syndrome, cleft lip and palate patients, and short- and long-term effects of nasoalveolar molding have been evaluated using three-dimensional surface imaging [ 54 ].
Volumetric results are also valuable clinical tools to assess primary palate reconstruction in infants with cleft lip and palate.
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Clinical evaluation of facial morphology is still largely subjective and prevents accurate documentation of facial structure or the changes following various esthetic and reconstructive procedures [ 55 ]. Recent scanning technology innovations provided valuable methods for precise three-dimensional clinical documentation and objective qualitative and quantitative analysis of the human face. Several techniques such as laser scanning, ultrasound, computed tomography, magnetic resonance imaging, and electromagnetic digitization can analyze facial characteristics in three dimensions but stereophotogrammetric systems are becoming the instrument of choice in anthropometric research [ 54 , 56 ].
Stereophotogrammetry is a unique method which utilizes means of triangulation and camera pairs in stereo configuration to recover the 3D distance to features on the facial surface Figure 1 5 and As early as Burke and Beard discussed and introduced the concept [ 57 ]. Today, it is predominately used in plastic surgery, medical genetics, and research settings. A major advantage of the surface imaging system is a near-instantaneous image capture on the order of 1.
Upon acquisition, image quality can be immediately reviewed to determine whether repeat imaging is necessary due to blurring or absence of surface data. Furthermore, software tools are available to view and manipulate the image, facilitate landmark identification and calculate anthropometric linear, angular, and volumetric measurements.
The disadvantages of 3D photogrammetry are its relative expense, limited availability, difficulties in recording shiny, shadowed, or transparent facial structures, and lack of ability to calculate interactive landmarks.
Three-dimensional surface imaging enables assessment of the spatial position of soft-tissue facial landmarks by assigning coordinates to each point. It could be difficult to identify a substantial number of landmarks and place them accurately in the three planes of space to gain a comprehensive understanding of the facial structure Figure 16 [ 58 - 63 ]. In a reproducibility study of 3D facial landmarks, Hajeer et al. Three sessions of landmark digitization were performed within a week interval.
Each landmark had x, y, and z coordinates given by the software and the mean differences were calculated from the three identification sessions by identifying the differences between the individual coordinate points. The results showed that 20 of the chosen landmarks had high reproducibility based on accepted 0. The following landmarks whose localization depended on the underlying skeleton had problems of reproducibility: menton, left and right zygion, and left and right gonion x-coordinate ; left and right zygion, left and right gonion, left and right tragion, and glabelle y-coordinate ; menton, left and right otobasion inferius, left and right tragion, and left and right gonion z-coordinate [ 62 ].
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In a different study, facial landmarks with distinct margins or borders also showed higher degree of consistent identification than those located on gently curved rounded surfaces. Several types of 3D photogrammetric imaging systems have been described and evaluated in the literature, e.
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Aldridge et al. Weinberg et al. These three techniques yielded a high degree of agreement among selected anthropometric variables, and the intraobserver precision was high for each method [ 65 ]. Manipulation of the scans and precise landmark identification requires proficiency with 3D computer software [ 53 ]. It has been suggested that head position, projection, and stabilization should be consistently the same in order to achieve optimum standardized settings.
Several internal module failures of the software while initiating a new series of scan, clearing the cache after scans, or modifying the location of already placed landmarks are still to be addressed by the manufacturer [ 69 ]. Direct comparison of multiple faces is challenging due to the diverse size and orientation of each face. Facial average methods like the Generalized Procrustes Analysis GPA have been proposed where the scans are scaled and fitted into equal size reference frames [ 60 ]. This implies that transition and rotation are applied in order to eliminate size difference between facial scans and equilibrate the squared summed distances between corresponding facial landmarks.
To obtain linear measurements, surface areas, and color mapping, a facial shells superimposition can be applied using the best-fitting alignment method or registration over relatively stable anatomical reference points and planes. A study evaluating facial scans of children aged In order to validate and elaborate the correlation and matching process between facial images and dental casts, Rosati et al.
The present anterior teeth in both facial and dental acquisitions were used as reference in the open-lips image superimpositions. In the closed lips image superimpositions the following facial soft-tissues landmarks were marked on the face before each acquisition and were used as fiducial points: Ftl, frontotemporale left; Ftr, frontotemporale right; and N, nasion. Seven linear measurements were virtually and directly performed between the facial landmarks and the occlusal plane on each subject.
The results showed mean relative error smaller than 1.
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The matching process was also found within a tolerable anthropometric and clinical context: the forehead mean distance in the open and closed lips image acquisitions was 0. Over the past 20 years, a number of 3D facial databases containing static and time sequence of images have been built with the purpose of aid in automatic face recognition and analysis algorithms. Several publicly available databases have facilitated the research for tracking and superimposition of 3D facial shells and feature extraction methodologies.
However, most of the existing 3D expression datasets are of small size comprising of deliberately posed or exaggerated expressions mostly of the six universal emotions e. Spontaneous behaviors have been suggested to vary in timing and appearance from acted ones. For instance, deliberate smiles have faster onset and offset and larger amplitude than the velocity and amplitude of genuine smiles [ 71 ]. Additional databases of recorded micro-expressions and dynamic 3D faces captured in wider range of contexts, unprompted behaviors, and affective states will have to be designed. Production sequential 3D surface imaging systems 4D Facial Dynamics are commercially available to provide a quantifiable understanding of soft tissue mobility, true anatomical motion, and facial expression [ 72 ].
The 4D systems are used to assess facial function in conjunction with natural head movements, functional progress and outcomes for patients undergoing dental treatment and surgical interventions. Human face is capable of making unique microexpressions which can be of very low intensity and last less than 0.
Therefore, the dynamic systems continuously track frame by frame the facial surface movements in order to achieve accuracy in understanding the tracking motions. The 4D technology acquires exact 3D surface information at approximately 60 frames per second from various coordinated standpoints for up to a 10 minute acquisition high resolution cycle.
The video sequence of the area of interest is recorded with grey-scale cameras record while the surface texture is captured with a color camera [ 73 ]. A unified point cloud continuous image is displayed from the viewpoints of two or more stereo cameras, reducing the errors from the stitching process of different datasets. Motion capture systems with automatic facial landmark recognition software have been found practical objective solutions for the soft tissue quantification movements.
Assessment of facial animation could be an essential part for orthodontic diagnosis and craniofacial abnormality, virtual surgical planning, and treatment outcomes. Furthermore, various surgical interventions could affect the function of nerves and associated musculature which could influence the magnitude and the speed of the soft tissue motions.
Shujaat et al. The similarity of the facial animation pattern before and after the surgery was calculated after eliminating the head motion and aligning the movement curves using the right and left endocanthion and pronasale as stable landmarks unaffected by the surgery. The results showed that the velocity of all landmarks was lower after the surgery; the smile animation difference was the least Mouth width maximum change after the surgery was found to be for lip purse 3.
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Lip purse animation similarity was highest 0. The 4D dynamic devices have also been employed for interlandmark and vector deviations, and shape and gender comparisons [ 74 ]. Virtual and sound animations have been incorporated in some of the recent system improvements [ 75 ]. Those materials are joined in successive layers one on top of the other through additive processes under automated computer control. The 3D printing process usually begins with a 3D model, virtually designed or obtained through scanning of a physical object.
Slicing software automatically transforms the point cloud into a stereolithographic file which is sent to the additive manufacturing machine for building the object Figure Today, 3D printing has grown to be competitive with the traditional model of manufacturing in terms of reliability, speed, price, and cost of use. In comparison with other technologies, additive manufacturing is more effective due its ability to use readily available supplies, recycle waste material, and has no requirements for costly tools, molds, or punches, scrap, milling, or sanding.
Additive manufacturing is likely to continue rapid growth in conjunction with intraoral scanning technology as a more effective system for orthodontic practices and laboratories for automatic fabrication of high-resolution study models, retainers, metal appliances, aligners, and indirect bonding, accelerating the production time and increasing the capability [ 15 , 77 ]. Currently, there is a huge selection of available 3D printing technologies suitable for orthodontic use:. Fused depositing modelling FDM is frequently used for modelling, manufacture applications, and prototyping.
The technology was introduced by S. Scott Crump towards the end of s and was popularized by Stratasys, Ltd in [ 1 ]. FDM employs the "additive" method of laying down thermoplastic material in layers. In order to produce a part the material is supplied through a heated nozzle after a metal wire or a plastic filament wound in a coil are released. The melted material hardens immediately after extrusion, thus minimizing inaccuracies [ 81 ]. The nozzle can be directed in both vertical and horizontal lines by a numerically controlled software mechanism.
Several materials such as acrylonitrile butadiene styrene ABS polymer, polyphenylsulfones and waxes, polycaprolactone, polycarbonates, polyamides, lignin, among many others, with diverse strength and thermal properties are available. Another approach to produce a 3D structure is for the material to be supplied from a basin through a small nozzle such as in the case of the 3D Bioplotter EnvisionTEC, Gladbeck, Germany.
The device is mainly applied in prototyping porous scaffolds for medical tissue engineering and organ bio-printing [ 82 ].
With an accuracy of just a few micrometers, the bioplotter is able to build body parts with different microstructural patterns including blood vessels, bone, and soft tissue. FDM is the most widely used process of 3D printing today, although there are other almost identical technologies like MakerBot Stratasys, Ltd. Laser based additive manufacturing, such as selective laser melting SLM and selective laser sintering SLS , uses power in the form of a high energy laser beam directed by scanning mirrors to build three-dimensional objects by melting metallic powder and fusing the fine particles together [ 83 ].
The process which can include partial and full melting or liquid-phase sintering is recurring layer after layer until the object is completed. The technology is commonly utilized due to its ability to form parts with complex geometries with very thin walls and hidden channels or voids directly from digital CAD data. Electron beam melting EBM is a type of additive manufacturing for laying down successive layers and creating near-net-shape or highly porous metal parts that are particularly strong, void-free, and fully dense.
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The EBM technology uses the energy source of an electron beam, as opposed to a laser [ 85 ]. Objects are manufactured layer by layer from fully melted metal powder utilizing a computer controlled electron beam in a high vacuum. EBM is able to form extremely porous mesh or foam structures in a wide range of alloys including stainless steel, titanium, and copper.
The technology is commonly used in orthopedic and oral and maxillofacial surgery for manufacturing customized implants.