HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hajeer, M. Y. Articles by Siebert, J. P. Search for Related Content PubMed PubMed Citation Articles by Hajeer, M. Y. Articles by Siebert, J. P.

Current Products and Practices

Applications of 3D imaging in orthodontics: Part I

University of Albaath Dental School, Damascus, Syria

D. T. Millett, A. F. Ayoub and J. P. Siebert

Glasgow University, Glasgow, UK

Address for correspondence: Dr M. Y. Hajeer, Senior Lecturer, Orthodontic Department, University of Albaath Dental School, P.O Box 9309, Mazzeh, Damascus, Syria. Email: hajeer{at}scs-net.org

	Abstract

Top Abstract Introduction Historical background General 3D concepts 3D imaging of the... Vision-based scanning techniques Applications of 3D imaging... References

 
Part I of this paper describes the background, general concepts, available techniques and the clinical applications of recording external craniofacial morphology in three dimensions. Part II explores the different 3D techniques of imaging the dental arches, and their possible uses in orthodontic diagnosis and treatment.

Key words: 3D Facial Imaging, Stereophotogrammetry, Facial Assessment, Study Models Archiving, Virtual Orthodontic Patient

	Introduction

Top Abstract Introduction Historical background General 3D concepts 3D imaging of the... Vision-based scanning techniques Applications of 3D imaging... References

 
Three-dimensional (3D) imaging has evolved greatly in the last two decades and has found applications in orthodontics, as well as in oral and maxillofacial surgery. In 3D medical imaging, a set of anatomical data is collected using diagnostic imaging equipment, processed by a computer and then displayed on a 2D monitor to give the illusion of depth. Depth perception causes the image to appear in 3D.¹

The applications of 3D imaging in orthodontics include pre- and post-orthodontic assessment of dentoskeletal relationships and facial aesthetics, auditing orthodontic outcomes with regard to soft and hard tissues, 3D treatment planning, and 3D soft and hard tissue prediction (simulation). Three-dimensionally fabricated custom-made archwires, archiving 3D facial, skeletal and dental records for in-treatment planning, research and medico-legal purposes are also among the benefits of using 3D models in orthodontics.

Part I of this paper focuses on the techniques that record the external craniofacial morphology and their applications (i.e. 3D imaging of the face), whereas Part II will evaluate the applications of direct or indirect recording of dental morphology (i.e. 3D imaging of the teeth).

	Historical background

Top Abstract Introduction Historical background General 3D concepts 3D imaging of the... Vision-based scanning techniques Applications of 3D imaging... References

 
From the introduction of the cephalostat, Broadbent stressed the importance of coordinating the lateral and postero anterior cephalometric films to arrive at a distortion-free definition of skeletal craniofacial form.² The first reports on implementation of this method were by Singh and Savara³ on 3D analysis of maxillary growth changes in girls. Computer programs have since been developed to collect three-dimensional coordinates directly from digital cephalogram images, eliminating the need for hand tracing and mouse-based X–Y digitizing tablets.^4,5

Stereophotogrammetry has evolved from old photogrammetric techniques to provide a more comprehensive and accurate evaluation of the captured subject. This technique uses one or more converging pairs of views to build up a 3D model that can be viewed from any perspective and measured from any direction. The earliest clinical use of stereophotogrammetry was reported by Thalmann-Degan in 1944 (according to Burke and Beard⁶) who recorded change in facial morphology produced by orthodontic treatment. With great advances in computer technology, a new generation of computerized stereophotogrammetric techniques has arisen making the capturing and building procedures quicker, simpler and more accurate.

On the other hand, the first commercial Computerized Tomography (CT) scanner appeared in 1972. Soon after, it was apparent that a stack of CT sectional images could be used to generate 3D information. In the early 1980s, researchers began investigating 3D imaging of craniofacial deformities. The first simulation software was developed for craniofacial surgery in 1986. Shortly after, the first textbooks on 3D imaging in medicine appeared with a concentration on the principles and applications of 3D CT- and MRI-based imaging. Three-dimensional imaging has evolved into a discipline of its own, ‘dealing with various forms of visualization, manipulation and analysis of multidimensional medical structures’.⁷

	General 3D concepts

Top Abstract Introduction Historical background General 3D concepts 3D imaging of the... Vision-based scanning techniques Applications of 3D imaging... References

 
Before exploring the different techniques available, it is necessary to understand some of the principles and terminology in 3D imaging. In two-dimensional (2D) photographs or radiographs, there are two axes (the vertical and the horizontal axes), while the Cartesian coordinates system in 3D images consists of the x-axis (or the transverse dimension), y-axis (or the vertical dimension), and the z-axis (the anteroposterior dimension ‘depth axis’). Figure 1 illustrates the right-handed xyz coordinate system, which is used in 3D medical imaging. The x-, y- and z-coordinates define a space in which multidimensional data are represented and this space is called the 3D space.⁷

View larger version (74K): [in this window] [in a new window]   Figure 1 Right-handed xyz coordinates system

View larger version (74K): [in this window] [in a new window]   Figure 2 Texture images captured by color cameras are mapped onto the 3D model to produce the ‘photorealistic rendered model’. In order to cover the face from ear to ear, two texture maps are captured from two different angles in front of the face. These images are taken simultaneously to prevent any error due to change in facial expression

• slice imaging, e.g. a set of CT axial data to produce reconstructed 2D images;
  
• projective imaging, e.g. surface laser scanning to produce what is considered a 2.5-D mode of visualization;
  
• volume imaging, e.g. holography or ‘varifocal mirrors’ techniques.
  

Projective imaging is the most popular 3D imaging approach, but it does not provide a true 3D mode of visualization similar to what is offered by the volume imaging approach.

For measuring scanned objects in 3D, there are two main geometrical strategies: orthogonal measurement and measurement by triangulation.⁸ Orthogonal measurement means that the object is sliced into layers. The x and y dimensions are measured directly on the slice surface, and the z dimension is measured by tallying the number of slices in the area of interest. An example of this method is the ordinary CT scan. Measurement by triangulation is analogous to the geometry of mammalian stereoscopic vision.⁸ Simply, two images of the object need to be captured from two different views simultaneously or in rapid succession. Stereophotogrammetry depends on this method of measurement, as well as both biplanar and coplanar stereo X-ray systems.

	3D imaging of the face

Top Abstract Introduction Historical background General 3D concepts 3D imaging of the... Vision-based scanning techniques Applications of 3D imaging... References

 
A broader description of these techniques is given elsewhere.⁹ The most common ones are highlighted.

3D cephalometry
Despite several improvements in 3D cephalometric research with more advanced armamentarium,^4,10 this technique is time-consuming, exposes the patient to radiation, does not define soft tissues and there are difficulties in relating accurately the same landmarks in the two radiographs, especially in the biplanar technique.^9,11

3D CT scanning
This technique has gained considerable popularity and applications in the medical field, but with regard to facial imaging, its main disadvantages are considered to be:

• patient exposure to a high dose of ionizing radiation;
  
• limited resolution of facial soft tissues due to slice spacing;
  
• the possibility of having artifacts created by metal objects inside the mouth.⁹
  

3D laser scanning
Laser scanning provides a less invasive method of capturing the face for planning or evaluating outcome of orthodontic or orthodontic-orthognathic surgical treatment. However, this technique has several shortcomings for facial scanning. They include:

• the slowness of the method, making distortion of the scanned image likely;
  
• safety issues related to exposing the eyes to the laser beam, especially in growing children;
  
• inability to capture the soft tissue surface texture, which results in difficulties in identification of landmarks that are dependent on surface color. Even with the new white-light laser approaches that capture surface texture color, the shortcomings persist.⁹
  

	Vision-based scanning techniques

Top Abstract Introduction Historical background General 3D concepts 3D imaging of the... Vision-based scanning techniques Applications of 3D imaging... References

 
These techniques are totally non-invasive, non-contact and vision-based imaging systems.

Moiré topography
Moiré topography delivers 3D information based on the contour fringes and fringe intervals. Difficulties are encountered if a surface has sharp features. Better results can be obtained on smoothly contoured faces. However, great care is needed in positioning the head, as a small change in head position produces a large change in fringe pattern. A 3D facial measuring system was proposed by Motoyoshi et al.,¹² but this system does not capture the normal facial texture and subsequent landmark identification is difficult.

Structured light techniques
In the structured light technique, the scene is illuminated by a light pattern and only one image is required (compared with two images with stereophotogrammetry). The position of illuminated points in the captured image compared to their position on the light projection plane provides the information needed to extract the 3D coordinates on the imaged object.¹³ However, to obtain high-density models, the face needs to be illuminated several times with random patterns of light. This increases the capture time with increased possibility of head movements. In addition, the use of one camera does not provide a 180° (ear to ear) facial model, which necessitates the use of several cameras or rotating the subject around an axis of rotation, which is not practical and has resulted in reduced applicability of this technique.¹⁴

Techalertpaisarn and Kuroda¹⁵ used two LCD projectors, charge-coupled device (CCD) cameras, and a computer to produce a three-dimensional image of the face that can be edited, shifted or rotated easily in any direction. This system needs at least 2 seconds to capture an image, which may be too long to reliably avoid head movements, especially when dealing with children.

Another variant of this technique was reported by Curry et al.¹⁶ Their system consists of two cameras and one projector. A color-coded light pattern is projected onto the face before each image is acquired. The displacement of the pattern enables the software to compute an accurate 3D model. Another image is acquired without any accompanying light pattern, to be used for texture mapping. Three acquisitions are needed (one frontally and two obliquely) to cover the whole face. In a further step, the three stereo-images are ‘stitched’ together using specific software. The produced 3D facial maps are integrated with other 3D skeletal and 3D dental maps.

Stereophotogrammetry
Stereophotogrammetry refers to the special case where two cameras, configured as a stereopair, are used to recover 3D distances of features on the surface of the face by means of triangulation.⁹

The technique has been applied clinically by using a portable stereometric camera optically linked with a simple plotting instrument.⁶ The incorporation of recent technology in computer science in the field of stereophotogrammetry has given the ability to process complex algorithms in order to convert simple photographs to three-dimensional measurements of facial changes. Ras et al.¹⁷ have demonstrated a stereophotogrammetric system that gives the three-dimensional coordinates of any chosen facial landmark, so linear and angular measurements could be calculated to detect any changes in facial morphology. This system consists of two synchronized semi-metric cameras mounted on a frame with a distance of 50 cm between them and positioned convergently with an angle of 15°.

The C3D® imaging system has been developed as the result of collaboration between Glasgow University Dental School and the Turing Institute. C3D® is based on the use of stereo digital cameras and special textured illumination, with a capture time of 50 milliseconds and it is sufficiently cost effective to be utilized within the daily clinical routine. C3D® captures the natural surface appearance of the patient’s skin and ‘drapes’ this skin texture over the captured 3D model of the face (Figure 3). So, C3D® affords the clinician a life-like 3D model of the patient’s head that can be rotated, enlarged, and measured in three dimensions as required for diagnosis, treatment planning and surgical outcome analysis.^9,11,18 The system has been validated and its accuracy was reported to be within 0.5 mm.¹⁹

View larger version (136K): [in this window] [in a new window]   Figure 3 The whole merged 3D face is a composite of two halves, each half representing the image acquisition from each pod. Top left: wireframe range models without any surface texture. Top right: facial texture maps of both sides. Bottom: 3D rendered polygonal meshes with textures enforced

3D Facial Morphometry (3DFM)
Although this is not a ‘true’ imaging system, it employs two CCD cameras that capture the subject, real time hardware for the recognition of markers and a software for the 3D reconstruction of landmarks’ x, y, z, coordinates relative to the reference system.²² Landmarks are located on the face and then covered with 2 mm hemispheric reflective markers. An infrared stroboscope is used to light up the reflective markers. Two-side acquisition is usually needed to capture the whole face.²²

Placement of landmarks on the face is time- and labor-consuming. Reproducibility of landmark identification is questionable. Change of facial expression between the two acquisition sessions increases the magnitude of error. No life-like models can be produced to show the natural soft-tissue appearance of the face. As a result, this system cannot be used as a 3D treatment-planning tool or as a communication media with orthodontic or orthognathic patients.

	Applications of 3D imaging of the face

Top Abstract Introduction Historical background General 3D concepts 3D imaging of the... Vision-based scanning techniques Applications of 3D imaging... References

 
Assessment of facial deformity, and the outcome of surgical and/or orthodontic correction
For the subjective assessment of deformities, 3D models are very valuable media for locating the source of deformity and its magnitude. Although the nature of patients’ facial deformities is usually expressed in three dimensions, diagnosis of these deformities has been made principally using 2D records (photographs and radiographs). Three-dimensional models can be manipulated in any direction, which gives considerable information to the orthodontist without the need for patient recall or being restricted by the time of clinical assessment (Figure 4). Assessment of outcome can also be performed easily by visual comparison of pre- and post-treatment models placed side by side. Figure 5 illustrates an example of an orthognathic patient treated by bi-maxillary surgery, where the face has been scanned using stereophotogrammetry (C3D® system).

View larger version (61K): [in this window] [in a new window]   Figure 4 3D imaging of the face enables the orthodontist to evaluate the face from any direction. Here, a skeletal Class III case is displayed in different views, with gradual rotations around the y-axis from –90° to +90° (middle row). +30° and –30° rotations around the x-axis are shown in the upper and lower rows, respectively

View larger version (105K): [in this window] [in a new window]   Figure 5 A Skeletal Class II case shown 1 month before and 6 months after orthognathic surgery

View larger version (84K): [in this window] [in a new window]   Figure 6 Mathematically superimposed pre- and post-surgical 3D models of a Class III patient. This patient has been treated by bi-maxillary surgery to advance the maxilla and setback the mandible. Seven points across the eyes and the nose are used for the superimposition. Displacements of residual facial soft tissue landmarks can be calculated and an objective assessment of the change can be obtained

Communication tool
Instead of discussing treatment objectives and treatment options using X-ray viewers, 2D photographs or composite tracings, life-like 3D models provide a very clear tool for showing areas of deformities, levels of asymmetry and relative relationships between different components of the face, all of which are in an interactive manner on-screen in front of the patient. Patient care is aided by the ability to share patients’ 3D records over distance between colleagues. ‘Tele-orthodontics’ is one of the promising applications of having complete 3D records of patients, especially in cases where inter-disciplinary treatment is required.

	References

Top Abstract Introduction Historical background General 3D concepts 3D imaging of the... Vision-based scanning techniques Applications of 3D imaging... References

 
1 Seeram E. 3-D imaging: basic concepts for radiologic technologists. Radiol Technol 1997; 69: 127–44.

2 Broadbent BS. A new X-ray technique and its application to orthodontia. Angle Orthod 1931; 1: 45–66.

3 Singh IJ, Savara BS. Norms of size and annual increments of seven anatomical measures of maxillae in girls from three to sixteen years of age. Angle Orthod 1966; 36: 312–24.[Medline]

4 Dean D, Hans MG, Bookstein FL, Subramanyan K. Three-dimensional Bolton-Brush Growth Study landmark data: ontogeny and sexual dimorphism of the Bolton standards cohort. Cleft Palate Craniofac J 2000; 37: 145–56.[CrossRef][Medline]

5 Subramanyan K, Dean D. Scanned bi-orthogonal radiographs as a source for 3D cephalometric data. SPIE 1996; 34: 717–24.

6 Burke PH, Beard FH. Stereophotogrammetry of the face. A preliminary investigation into the accuracy of a simplified system evolved for contour mapping by photography. Am J Orthod 1967; 53: 769–82.[CrossRef][Medline]

7 Udupa J, Herman G. 3D Imaging in Medicine. Boca Raton: CRC Press, 1991.

8 Baumrind S. Integrated three-dimensional craniofacial mapping: background, principles, and perspectives. Semin Orthod 2001; 7: 223–32.[CrossRef]

9 Hajeer MY, Ayoub AF, Millett DT, Bock M, Siebert JP. Three-dimensional imaging in orthognathic surgery — the clinical application of a new method. Int J Adult Orthod Orthognath Surg 2002; 17: 318–30.

10 Palomo JM, Dean D, Broadbent BJ. Three-dimensional craniofacial shape change in sixteen female Bolton faces. In McNamara JJ (Ed.) The Enigma of the Vertical Dimension, Craniofacial Growth Series, pp. 287–310. Ann Arbor: Ann Arbor Center for Growth and Development, University of Michigan, 2000.

11 Ayoub AF, Siebert P, Moos KF, Wray D, Urquhart C, Niblett TB. A vision-based three-dimensional capture system for maxillofacial assessment and surgical planning. Br J Oral Maxillofac Surg 1998; 36: 353–7.[CrossRef][Medline]

12 Motoyoshi M, Namura S, Arai HY. A three-dimensional measuring system for the human face using three-directional photography. Am J Orthod Dentofac Orthop 1992; 101: 431–40.[Medline]

13 Nguyen CX, Nissanov J, Ozturk C, Nuveen MJ, Tuncay OC. Three-dimensional imaging of the craniofacial complex. Clin Orthod Res 2000; 3: 46–50.[CrossRef][Medline]

14 Tuncay OC. Three-dimensional imaging and motion animation. Semin Orthod 2001; 7: 244–50.[CrossRef]

15 Techalertpaisarn P, Kuroda T. Three-dimensional computer-graphic demonstration of facial soft tissue changes in mandibular prognathic patients after mandibular sagittal ramus osteotomy. Int J Adult Orthod Orthog Surg 1998; 13: 217–25.

16 Curry S, Baumrind S, Carlson S, Beers A, Boyd R. Integrated three-dimensional craniofacial mapping at the Craniofacial Research Instrumentation Laboratory/University of the Pacific. Semin Orthod 2001; 7: 258–65.[CrossRef]

17 Ras F, Habets LL, van Ginkel FC, Prahl-Andersen B. Quantification of facial morphology using stereophotogrammetry – demonstration of a new concept. J Dent 1996; 24: 369–74.[CrossRef][Medline]

18 Ayoub AF, Wray D, Moos KF, Siebert P, Jin J, Niblett TB, et al. Three-dimensional modeling for modern diagnosis and planning in maxillofacial surgery. Int J Adult Orthod Orthog Surg 1996; 11: 225–33.

19 Ayoub AF, Garrahy A, Hood C, White J, Bock M, Siebert JP, et al. Validation of a vision-based three-dimensional facial imaging system. Cleft Palate Craniofac J 2003; 40: 523–9.[CrossRef][Medline]

20 Siebert JP, Marshall S. Human body 3D imaging by speckle texture projection photogrammetry. Sensor Review 2000; 20: 218–26.[CrossRef]

21 Available at: www.faraday.gla.ac.uk (accessed January 2004).

22 Ferrario VF, Sforza C, Poggio CE, Serrao G. Facial three-dimensional morphometry. Am J Orthod Dentofac Orthop 1996; 109: 86–93.[CrossRef][Medline]

23 Kobayashi T, Ueda K, Honma K, Sasakura H, Hanada K, Nakajima T. Three-dimensional analysis of facial morphology before and after orthognathic surgery. J Craniomaxillofac Surg 1990; 18: 68–73.[Medline]

24 McCance AM, Moss JP, Wright WR, Linney AD, James DR. A three-dimensional soft tissue analysis of 16 skeletal class III patients following bimaxillary surgery. Br J Oral Maxillofac Surg 1992; 30: 221–32.[CrossRef][Medline]

25 Moss JP, McCance AM, Fright WR, Linney AD, James DR. A three-dimensional soft tissue analysis of fifteen patients with Class II, Division 1 malocclusions after bimaxillary surgery. Am J Orthod Dentofac Orthop 1994; 105: 430–7.[Medline]

26 McCance AM, Moss JP, Fright WR, James DR, Linney AD. A three dimensional analysis of soft and hard tissue changes following bimaxillary orthognathic surgery in skeletal III patients. Br J Oral Maxillofac Surg 1992; 30: 305–12.[CrossRef][Medline]

27 McCance AM, Moss JP, Fright WR, James DR, Linney AD. A three-dimensional analysis of bone and soft tissue to bone ratio of movements in 17 Skeletal II patients following orthognathic surgery. Eur J Orthod 1993; 15: 97–106.[Abstract/Free Full Text]

28 Soncul M, Bamber MA. The optical surface scan as an alternative to the cephalograph for soft tissue analysis for orthognathic surgery. Int J Adult Orthod Orthog Surg 1999; 14: 277–83.

29 Morris DO, Illing HM, Lee RT. A prospective evaluation of Bass, Bionator and Twin Block appliances. Part II — the soft tissues. Eur J Orthod 1998; 20: 663–84.[Abstract/Free Full Text]

30 Ismail SF, Moss JP, Hennessy R. Three-dimensional assessment of the effects of extraction and nonextraction orthodontic treatment on the face. Am J Orthod Dentofac Orthop 2002; 121: 244–56.[CrossRef][Medline]

31 McCance AM, Moss JP, Fright WR, Linney AD, James DR. Three-dimensional analysis techniques — Part 1: three-dimensional soft-tissue analysis of 24 adult cleft palate patients following Le Fort I maxillary advancement: a preliminary report. Cleft Palate Craniofac J 1997; 34: 36–45.[CrossRef][Medline]

32 Bourne CO, Kerr WJ, Ayoub AF. Development of a three-dimensional imaging system for analysis of facial change. Clin Orthod Res 2001; 4: 105–11.[CrossRef][Medline]

33 Ferrario VF, Sforza C, Poggio CE, Schmitz JH. Soft-tissue facial morphometry from 6 years to adulthood: a three-dimensional growth study using a new modeling. Plast Reconstr Surg 1999; 103: 768–78.[Medline]

34 Berkowitz S, Cuzzi J. Biostereometric analysis of surgically corrected abnormal faces. Am J Orthod 1977; 72: 526–38.[CrossRef][Medline]

35 Motegi N, Tsutsumi S, Okumura H, Yokoe Y, Iizuka T. Morphologic changes in the perioral soft tissues in patients with mandibular hyperplasia using a laser system for three-dimensional surface measurement. Int J Oral Maxillofac Surg 1999; 28: 15–20.[Medline]

This article has been cited by other articles:

				The use of 3D face shape modelling in dysmorphology Arch. Dis. Child., December 1, 2007; 92(12): 1120 - 1126. [Abstract] [Full Text] [PDF]

				T. K.L. Schleyer, T. P. Thyvalikakath, P. Malatack, M. Marotta, T. A. Shah, P. Phanichphant, G. Price, and J. Hong The feasibility of a three-dimensional charting interface for general dentistry J Am Dent Assoc, August 1, 2007; 138(8): 1072 - 1080. [Abstract] [Full Text] [PDF]

				L. Joffe Current Products and Practices OrthoCADTM: digital models for a digital era J. Orthod., December 1, 2004; 31(4): 344 - 347. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hajeer, M. Y. Articles by Siebert, J. P. Search for Related Content PubMed PubMed Citation Articles by Hajeer, M. Y. Articles by Siebert, J. P.