GENERAL
`
`I N B R I E F
`• Describes how electronic 3D images for
`use in clinical dentistry can be produced
`using both contact and non-contact
`methods.
`• Highlights how these images can be used
`in the different dental disciplines.
`• However the original is scanned, the
`output generated is composed of a
`discrete series of data points in 3D,
`which is used to recreate the fi nal
`surface image.
`
`3D surface imaging in dentistry
`– what we are looking at
`
`A. J. Ireland,1 C. McNamara,2 M. J. Clover,3 K. House,4 N. Wenger,5
`M. E. Barbour,6 K. Alemzadeh,7 L. Zhang8 and J. R. Sandy9
`
`3D imaging has been widely used within various fields of dentistry to aid diagnosis, in treatment planning and appliance
`construction. Whereas traditionally this has involved the use of impression materials together with plaster or stone models,
`modern techniques are continually evolving which use virtual 3D images. These electronic virtual images are created using
`either contact or non-contact optical scanning techniques, but there are limitations, the most important of which is that
`any new virtual surface image is created from a series of discrete data points. It is not created from a continuous stream of
`data relating to the original object. This means that computer software has to be used to recreate a possible best fi t, virtual
`surface from the data obtained. This paper describes the principles behind 3D scanning technology, the limitations of 3D
`imaging as well as current and possible uses of such imaging in clinical dentistry.
`
`Introduction
`Within dentistry there has always been
`a requirement to record and manipu-
`late three dimensional (3D) replicas of
`patients’ tissues. To date this has pre-
`dominantly been in the form of impres-
`sions and plaster or stone models. Whilst
`these have the advantage of dimensional
`accuracy, familiarity and ease of han-
`dling, they also possess a number of
`disadvantages, the principal ones being
`the time and the facilities required for
`fabrication, cataloguing, storage and
`retrieval. In recent years there have been
`developments in electronic 3D imag-
`ing that have led to an increasing use
`in dentistry, including restorative den-
`tistry, orthodontics, and orthognathic
`and craniofacial surgery. It is easy to
`take such developments for granted and
`
`1*Senior Lecturer and Consultant in Orthodontics,
`2Specialist Registrar in Orthodontics, 3Specialist Reg-
`istrar in Orthodontics, 4Senior Specialist Registrar in
`Orthodontics, 6Lecturer in Dental Materials Science and
`Biomaterials, 9Professor in Orthodontics, Bristol Dental
`School; 5Consultant in Orthodontics, Royal Cornwall
`Hospital; 7Senior Lecturer, 8Postgraduate Student,
`Mechanical Engineering, Bristol University
`*Correspondence to: Dr Tony Ireland, Bristol Dental
`School, Lower Maudlin Street, Bristol, BS1 2LY
`Email: tony.ireland@bristol.ac.uk
`
`Refereed Paper
`Accepted 30 May 2008
`DOI: 10.1038/sj.bdj.2008.845
`©British Dental Journal 2008; 205: 387-392
`
`to automatically assume the images pro-
`duced are accurate and reliable repre-
`sentations of the original. It is useful for
`the practising dentist to have an under-
`standing of how such digital images are
`produced and indeed consider what we
`are actually looking at.
`
`What are the principles
`behind 3D surface imaging?
`3D surface scanners, as the name sug-
`gests, are devices that create a digital
`map of the surface of an object and
`collect data on its three dimensional
`shape and size. The raw data are usually
`obtained in the form of a point cloud,
`representing the 3D coordinates of the
`digitised surface. In practice there are
`two main categories of 3D surface scan-
`ners: contact and non-contact scanners.
`These will be described in turn.
`
`Contact scanners
`Many contact scanners are CMMs (co-
`ordinate measuring machines) which are
`mechanical systems designed to move a
`measuring probe over a surface and to
`determine the coordinates of the points
`comprising the surface. They have four
`main components: the measuring probe,
`the control or computing system, the
`machine which moves the probe and the
`measuring software. The mechanical
`
`Fig. 1 The Incise contact probe scanner
`(Renishaw, Wotton-under-Edge,
`Gloucestershire, UK)
`
`measuring probe performs a linear or
`radial scan of the desired surface and, as
`it does so, the position of the stylus tip in
`the x, y and z planes is sampled at regu-
`lar intervals. This gives rise to an array
`of data points, or a ‘point cloud’, repre-
`senting points which lie on the object
`surface. An example of a contact probe
`scanner in use in dentistry is the Incise
`system (Fig. 1) (Renishaw, Wotton–
`under–Edge, UK), where the measuring
`probe has a ceramic shaft on the end of
`
`BRITISH DENTAL JOURNAL VOLUME 205 NO. 7 OCT 11 2008
`
`387
`
`© 2008 Macmillan Publishers Limited. All rights reserved.
`
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`

`

`GENERAL
`
`which is a ruby ball. This type of scan-
`ner can only usefully be used on hard
`surfaces such as dental stone, as a soft
`surface will either deform or wear when
`in contact with the probe. These scan-
`ners are used in the dental laboratory to
`obtain surface scans of tooth prepara-
`tions. The 3D information is then used
`to mill alumina crown copings. Whilst
`contact probe scanning is very accu-
`rate, the scanning process is relatively
`slow when compared to non-contact
`optical systems.
`
`Non-contact optical scanners
`Many 3D laser scanners employ the
`principle of triangulation, familiar to
`most people from the fields of cartog-
`raphy and surveying, to obtain 3D sur-
`face images. A laser beam is incident on
`the surface of the object to be scanned
`and a camera-like device, such as a
`charge-coupled device (CCD) or position
`sensitive detector, is used to record the
`location of the point at which the laser
`beam strikes the object. Since the posi-
`tions of both the laser and camera and
`the angle between them is known, the
`position of the surface can be calculated
`using simple triangulation. The meas-
`urement accuracy is mainly dependent
`on the accuracy of the image acquired
`from the object surface by the detector.1
`However, beam reflection and stray light
`will affect the measurement accuracy,
`as will differences in the topography
`and finish of the object under investiga-
`tion relative to the calibration surface.
`It is therefore important to calibrate the
`scanner on a surface with similar prop-
`erties to the object to be scanned. Laser
`scans can either be created from a point
`which is progressively scanned over
`the object surface, or more rapidly by
`imaging the object with a series of laser
`lines or profiles. A potential problem
`can occur when a series of parallel laser
`lines progressively scan over an object
`surface. If there is a steep change in the
`object surface such as a void, as the fi rst
`laser line passes into this void it may
`pass out of site of the detector or camera,
`which may then mistake the second laser
`line, yet to pass over the void, as the
`first line. Errors can then occur when
`the
`image
`is reconstructed by the
`computer software.
`
`388
`
`Fig. 2 Digital fringe projection on a
`dental model35
`
`Fig. 3a The point cloud of an upper
`plaster model where the teeth are easily
`visualised
`
`Photogrammetry, like laser scanning,
`also employs the principles of triangula-
`tion, but instead of a laser beam it uses
`a series of photographs of the object of
`interest. Variations on this method use
`aspects of photographic images such as
`defocus, shading and scaling which can
`help give an estimate of 3D shape and
`depth. The major drawback of this tech-
`nique is that it is not possible to obtain
`the dense point clouds required for free-
`form surface modeling and accurate
`CAD surface reconstruction. Reconstruc-
`tion of the acquired image can also be
`time consuming.
`Interferometric
`techniques may use
`laser or white light. Interferometry uses
`the principle that waves will interact
`with one another causing interference.
`If waves are perfectly in phase they
`reinforce each other, but if they are per-
`fectly out of phase (and of equal ampli-
`tude) they will cancel each other out.
`In interferometric shape measurement,
`light of different wavelengths (colours)
`is projected along a single beam onto a
`surface. The interference between the
`wavelengths depends on the distance
`between the source and the surface, thus
`fringes of dark and light are formed on
`the object which relate to the topogra-
`phy of the surface. In a sense, the inter-
`ference fringes can be considered to be
`forming contours such as those seen on
`an Ordnance Survey map. The advan-
`tages of interferometry include high
`resolution, a long range, and they are
`also relatively insensitive to mechani-
`cal vibrations. Multiple variants have
`been developed.
`The Structured Light Method uses a
`well-characterised simple image which
`is projected onto the surface to be inves-
`tigated. This image is often an array
`of black (dark) and white (bright) lines
`
`Fig. 3b The same model as Figure 3a
`viewed from a different angle where
`visualisation of the individual teeth
`within the point cloud is very diffi cult
`
`or a ‘checkerboard’ of black and white
`squares. Unless the surface is perfectly
`flat, the image will appear deformed.
`Therefore it will no longer look like an
`array of lines or squares but will take
`on a new appearance, which is a com-
`bination or superposition of the origi-
`nal image and the surface topography.
`The pattern images captured by the CCD
`camera are digitised and the phase dis-
`tribution in the patterns is obtained by
`phase analysis techniques, such as Fou-
`rier transforms or phase stepping tech-
`niques.2 In other words, once the image
`is captured a computer algorithm is used
`to ‘decode’ the surface topography from
`the difference between the projected
`image and the original image. Figure
`2 shows a sample process of the digital
`fringe projection technique.3 The main
`advantages of this method of 3D opti-
`cal scanning are the high speed, low
`cost and high accuracy. It is used in
`the 3dMd facial imaging system.4 How-
`ever, the technique is not without its
`problems as issues such as shading and
`surface holes or crevices will present
`problems with image projection and
`subsequent capture.
`The Moir fringe method is another pro-
`jection technique. Here, light projected
`
`BRITISH DENTAL JOURNAL VOLUME 205 NO. 7 OCT 11 2008
`© 2008 Macmillan Publishers Limited. All rights reserved.
`
`

`

`GENERAL
`
`although it might be relatively easy to
`visualise a tooth or teeth, as represented
`by the point cloud in one direction, when
`the same point cloud image is viewed
`from another direction it may not be as
`easy to visualise (Figs 3a-3b). In order
`to make the visualisation process more
`intuitive, computerised polygonisation
`of the point cloud is used to fabricate a
`virtual surface from the scan data.6 In
`this process the data points are linked to
`adjacent points within the cloud to make
`a polygon mesh. The polygon mesh usu-
`ally being composed of triangles join-
`ing three adjacent data points within
`the cloud. The scanned object surface is
`therefore represented as a series of fl at
`polygons, which in close up, although
`easier to view than the point cloud, might
`still make it difficult to visualise the sur-
`face. In addition it will also not replicate
`the original, relatively smooth surface of
`the scanned object. This will obviously
`depend to a large extent on the density of
`the point cloud. The greater the density,
`the more accurate and indeed the easier
`the surface visualisation will be.
`Although software can create the pol-
`ygon mesh from a single large scanned
`image, often the surface reconstruc-
`tion process begins with the point cloud
`being divided into several features (eg
`molar, premolar, incisor, etc). A poly-
`gonised surface is created for each of
`these individual features. Once this
`has been done, each can be shaded and
`textured to give a realistic appearance
`and the individual scanned and proc-
`essed components reassembled to create
`a final image. There are different types
`of shading that can be applied to such
`a rendered surface with examples being
`Gouraud and Phong shading.
`It should be remembered that the fi nal
`image – created by whatever technique –
`when made from a point cloud will have
`areas within it where there are no data
`concerning the scanned surface. This
`is because the data capture is not truly
`continuous, but is composed of discrete
`data points. Therefore, what we see in
`any final image may not be a true repre-
`sentation of the object surface.
`The production of the polygon mesh
`and then the further post-processing
`surface rendering relies on a consistent
`set of point cloud data, without missing
`
`Fig. 4 Comparison of the polygonised
`surface on the left with the original point
`cloud data on the right35
`
`onto the surface of interest passes
`through a grating. The projected image
`is picked up by a camera after the light
`has passed back through an identical
`reference grating. The interference pat-
`tern created, in the form of lines on the
`object surface, can be used to create a
`3D surface image, once again using tri-
`angulation techniques dependent on the
`position of the light and camera.
`
`Converting the scanned image
`data into a format that can be
`used clinically
`The raw data obtained from a 3D scan-
`ner is normally in the form of a point
`cloud, which represents the 3D coor-
`dinates in the x, y and z planes of the
`digitised surface (Fig. 3a). As the name
`suggests, this is a representation of each
`of the data points obtained from the
`image surface. The density of the point
`cloud and therefore how accurately it
`represents the imaged surface depends
`on numerous factors. These will include
`the capability of the particular scan-
`ner, both in terms of its hardware and
`software, how it is used by the operator
`and the time spent scanning. Missing
`data within the point cloud, for exam-
`ple as a result of an undercut, can pose
`problems when trying to accurately rep-
`resent the original image surface. It is
`not difficult to see that the acquisition
`of the 3D data points to create a suitably
`dense point cloud, without missing data,
`can be a time consuming process and
`may require multiple scans from various
`different directions.
`The production of the point cloud ena-
`bles the observer, in this case a dentist,
`to explore and manipulate the virtual 3D
`image on the computer screen.5 However,
`
`Fig. 5 Superimposed images of pretreatment
`(red) and post treatment (blue) models.
`Note how it is possible to then make a
`linear measurement of the change in canine
`position with treatment
`
`data points. If data points are missing
`then surface rendering is extremely
`difficult due to the algorithms usually
`defined within the rendering software.
`There are many types of such algorithms
`available.7 Figure 4 shows an example of
`surface polygonisation of half of a max-
`illa from the original point cloud.
`An example of a software package
`which is capable of creating surfaces
`from point cloud data, and which is in
`common use in engineering, is Image-
`ware.8 In addition to being able to accu-
`rately reconstruct complex 3D models,
`this software also enables detailed anal-
`ysis of images, including measurement
`between feature points and areas. For
`example, it is possible to scan pre and
`post treatment upper study models of
`a patient and determine changes from
`one to the other, provided a stable ref-
`erence landmark is available. One sug-
`gested reference is the medial aspect of
`the third palatal rugae. By superimpos-
`ing two surface models, as in Figure 5,
`where the before treatment model in red
`is superimposed on the post treatment
`model in blue, a 3D surface to surface
`evaluation can be realised virtually.
`Once the images have been acquired and
`processed, point to point measurement
`of treatment changes then becomes rela-
`tively straightforward. Using the same
`principles, it is also possible to measure
`linear and volumetric changes in teeth
`as a result of tooth erosion.9 Although
`3D imaging has applications within
`dental research, there are an increasing
`number of 3D imaging systems available
`with direct clinical applications and in
`various fields of dentistry.
`
`BRITISH DENTAL JOURNAL VOLUME 205 NO. 7 OCT 11 2008
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`© 2008 Macmillan Publishers Limited. All rights reserved.
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`

`

`GENERAL
`
`Restorative dentistry
`Within restorative dentistry, computer-
`aided design (CAD) and computer-aided
`manufacture (CAM) of indirect restora-
`tions became available approximately
`20 years ago.10 Since this time, the rapid
`development of computer-based technol-
`ogy has provided increasingly sophisti-
`cated replication and digitisation of the
`complex topography of tooth structures.
`One of the criteria that must be fulfi lled
`for any indirect restoration to be success-
`ful is an accurate fit to the tooth. This
`will be determined by the whole produc-
`tion process, but in particular the initial
`assessment of the surface topography of
`an object. In the case of a tooth, whether
`prepared or unprepared, it is composed
`of complex irregular geometric confi gu-
`rations that are unique in each case and
`where there is no exact reference form.11
`Even with these potential problems there
`are several advanced dental CAD/CAM
`systems now available. These include
`systems which are capable of directly
`scanning within the mouth, namely:
`• Cerec 3 (Sirona, Bensheim, Germany).
`This system scans preparations
`intraorally using infrared irradiation.
`Alternatively models can be scanned
`in the laboratory. The marginal fi t of
`crowns produced using this technique
`has been reported to be in the range
`of 60 to 100μm12,13
`• Hint-ELs® DentaCad System (Hint-
`ELS, Griesheim, Germany). This
`system is based on a visible light
`optical scanner
`• Lava (3M ESPE, Seefeld, Germany).
`Although already available as a labo-
`ratory based scanning system, it is
`soon to be introduced as an intra oral
`system based on a hand held wand
`using visible light. It can scan a sin-
`gle tooth up to a whole dental arch14
`• Cadent iTero. This system also uses
`visible light to scan single teeth or a
`whole dental arch.15
`
`Other systems create scans from plas-
`ter or stone models of the mouth, usually
`in the dental laboratory and include:
`• Cercon Ceramics (DeguDent, Dentsply
`International Co., Germany). This
`system comprises a non-contact
`laser scanner
`• Everest (KaVO, Lake Zurich, IL, USA).
`
`390
`
`This laboratory based system uses a
`visible light system with structured
`light projection
`• Incise (Renishaw, Gloucestershire,
`England). This is a contact
`probe system
`• Procera (Nobel Biocare, Göteborg,
`Sweden). This is also a contact
`probe system.
`
`It can be seen that using these mod-
`ern CAD/CAM systems, the geometry
`of the teeth, be it within the clinic or
`laboratory, can be digitised either
`using contact methods, such as coor-
`dinate measuring machines (CMMs) or
`non-contact methods (laser and opti-
`cal scanners). For fi xed prosthodontic
`treatment, laser, visible light or infrared
`scanners are used, predominantly in the
`clinical environment, for scanning the
`tooth preparation. Contact scanners are
`used exclusively in the laboratory set-
`ting, where the technician scans a die
`that has previously been cast in stone.
`An example of a contact probe scanner
`is the Renishaw Incise system, where a
`ruby ball contact probe scans the model
`surface in order to render a 3D compu-
`terised image. Using the data generated,
`a zirconia crown coping is then directly
`milled from a zirconia blank. An exam-
`ple of a non-contact optical method
`is the Cerec 3 system. In this case the
`tooth surface is directly scanned in the
`mouth using infrared radiation, which
`is reflected back from the tooth surface
`and detected by a charged couple device
`(CCD). Since the surfaces of enamel
`and dentine have differing degrees of
`reflectance with infrared light, the tooth
`is pre-treated with titanium dioxide
`powder prior to scanning. The 3D image
`is then used to mill ceramic restorations
`at the chairside.
`CAD/CAM technology has a number
`of actual, or at least potential, advan-
`tages when compared to traditional indi-
`rect dentistry. These include:16
`• No impression taking or casting,
`thereby reducing the number of man-
`ufacturing steps, which may improve
`the dimensional accuracy of the
`fi nal restoration
`• Direct chairside fabrication of
`various types of restoration in one
`appointment without the need for a
`
`provisional restoration. This not only
`improves the likely fit of a restora-
`tion, but also means the ever-present
`risk of loss or damage to a provisional
`restoration is removed
`• Reduced laboratory and chairside
`costs. However, there is the initial
`expenditure on the CAD/CAM
`equipment to consider, which may
`be very high.
`
`Both contact and non-contact scanners
`can also be used to monitor and quantify
`tooth surface loss over time. For exam-
`ple, accurate impressions can be used to
`create stone models, which can then be
`scanned using a contact probe, laser or
`visible light. In this way surface loss due
`to attrition, abrasion or erosion can be
`quantified both linearly and volumetri-
`cally, provided there are stable reference
`points available.17,18
`
`3D imaging in orthodontics
`Within orthodontics, electronic 3D
`imaging has several potential and cur-
`rent applications. The most obvious is
`as a substitute for conventional plaster
`study models. These models are used not
`only for initial diagnosis, but also as a
`means of monitoring treatment progress,
`as a reference against which archwires
`can be fabricated, as a demonstration
`of quality of outcome and as a medico-
`legal record. In the latter case 3D records
`are likely to be acceptable to the court
`provided there is a suitable audit trail to
`show that such an image has not been
`tampered with/manipulated, although a
`legal precedent is perhaps yet to be set.
`Digital study models are commercially
`available from several companies. One
`such company, OrthoCAD (Cadent, Fair-
`view, NJ, USA) creates digital images of
`dental casts using an optical scanner. To
`obtain the images, the orthodontist sends
`alginate impressions and a wax bite
`to the OrthoCAD laboratory. These are
`then converted into ‘plaster equivalents’
`for scanning and the scanned images
`are stored on the company’s server for
`accessing by the orthodontist.19 They
`are useful for routine measurement of
`tooth size, overjet, overbite and for Bol-
`ton analyses. The accuracy of digital
`study models relative to conventional
`plaster models has been the subject of a
`
`BRITISH DENTAL JOURNAL VOLUME 205 NO. 7 OCT 11 2008
`© 2008 Macmillan Publishers Limited. All rights reserved.
`
`

`

`GENERAL
`
`previous investigation. Although digital
`models were not found to be as accu-
`rate as the plaster models for certain
`measurements, eg tooth size and over-
`bite, the differences are thought prob-
`ably to be insignificant during routine
`clinical use.20
`Electronic 3D imaging can also be
`used for facilitating accurate bracket
`positioning, for wire bending and in
`appliance fabrication. Examples of the
`latter include the OrthoCAD iQ system,
`where conventional orthodontic brack-
`ets are positioned on the digital models,
`and positioners are fabricated to allow
`transfer of the brackets to the patient’s
`mouth for indirect bonding. Ormco’s
`Insignia™ system provides brackets with
`positioning jigs as well as custom made
`archwires. Here the digital images are
`created by a combined destructive proc-
`ess whereby patient models are sectioned
`into thin slices (typically 0.001’ to 0.006’
`thick)21 and each slice is laser scanned to
`provide data to reconstruct a 3D image
`of the dental arch. A similar technique,
`but this time using non-destructive laser
`scanning, is used in the fabrication of
`the lingual Incognito™ appliance (TOP
`Service für Lingualtechnik, GmbH).
`Here, custom made lingual appliances
`are computer generated on the digital
`models and then engineered in wax,
`before finally being cast in gold alloy for
`placement in the mouth. The archwires
`to be used during treatment are also fab-
`ricated using the same electronic data to
`fit this customised appliance.22
`Although digital models are created
`in the above techniques, they are still
`made by laser scanning models that have
`been cast from the patient’s impressions.
`In the Suresmile technique (OraMetrix,
`Inc, Texas, USA), appliance and archwire
`fabrication uses either a direct optical
`scan of the mouth, which can take up to
`45 minutes, or a scan of plaster models.
`The latter method has the advantage of
`saving clinical time, but it inevitably
`requires additional dental
`laboratory
`time. Newer systems are currently being
`developed that are likely to substantially
`reduce this scanning time, making rou-
`tine digital image acquisition rather than
`conventional impression taking a reality.
`There is currently a high demand for
`more aesthetic orthodontic appliances
`
`and to try to accommodate this, Align
`Technology (Santa Clara, CA, USA)
`reintroduced the concept of a series of
`transparent tooth positioners to treat
`malocclusion. Developed in the late
`1990s, the process involves creating
`positioners using
`stereolithography,
`directly from digital images. These
`images are created by CT (computed
`tomography) X-ray scanning the dental
`impressions, which eliminates the need
`for creating plaster models for subse-
`quent imaging. It has been reported
`that digital study models with a spatial
`resolution in the order of 45-50μm can
`be constructed using this CT scanned
`impression approach.23 However, the dis-
`advantage of CT scanning is the expense
`of the equipment and the time taken to
`acquire the image.
`Electronic 3D imaging of the face also
`has a role in orthodontics. The concept
`of using such 3D images in orthodon-
`tic diagnosis has been around for over
`60 years. Thalmann-Degen24 and Burke
`and Beard25 used stereophotogrammetric
`technology to create contour maps of the
`face, not only to aid diagnosis, but also
`to record changes in facial morphology
`as a result of growth.26 3D facial imaging
`might be useful in orthodontics in moni-
`toring the effects of treatments such as
`functional appliances and assessing the
`effects of extractions as part of ortho-
`dontic fixed appliance therapy.
`
`Orthognathic and
`craniofacial surgery
`Three-dimensional facial surface scan-
`ning has been used in orthognathic
`and craniofacial surgery to aid diagno-
`sis, to help monitor the short and long
`term effects of surgery and to assist in
`facial reconstruction.27 The scanners
`are either laser-based, or stereophoto-
`grammetric using structured light. In
`the latter instance two or more digital
`cameras are used to capture the images
`from which a 3D facial reconstruction is
`made, with the images being acquired
`in milliseconds and in full colour. An
`example of the latter is the 3dMDface™
`System (3dMD, London, UK). The origi-
`nal laser systems used in facial imag-
`ing, as described by Moss,28 were slow
`at image acquisition, taking up to 20
`seconds and with a reported accuracy
`
`of 0.5 mm. More recently systems such
`as the Konica-Minolta laser scanners,
`which are slit laser scanners rather than
`point lasers, are accurate to within 50
`μm and have much shorter scan times of
`0.3 seconds.
`In diagnosis, such 3D facial imaging
`can be used to help simulate the effects
`of orthognathic surgery on facial aes-
`thetics and thereby help in surgical
`planning, particularly in combination
`with x-ray CT scanning. However, some
`care needs to be exercised when using
`the 3D images, particularly when dem-
`onstrating to a patient the likely effects
`of any proposed surgery. It may unrea-
`sonably raise expectations as to the fi nal
`surgical outcome. In this respect, it is
`best to accept that the 3D image is used
`to simulate rather than predict facial
`change.29 This arises not as a result of
`the 3D imaging technique, but because
`there is an inherent difficulty in being
`able to predict, with any degree of accu-
`racy, the soft tissue changes as a result
`of surgically moving the underlying
`hard tissues.30,31
`Since 3D scanning enables not only
`linear measures of outcome of orthog-
`nathic surgery to be determined, but also
`volumetric changes, it means that the
`effect of factors such as post operative
`period and differing pharmacological
`interventions on facial swelling follow-
`ing surgery can also be assessed.32,33
`Where patients require facial recon-
`struction after tissue loss, as a result
`of trauma or malignancy, 3D scanning
`techniques can be used to map the area
`of deformity, mirror the area from the
`unaffected opposite side of the face and
`via rapid prototyping, recreate a facial
`prosthesis.34
`
`Summary
`It is easy to assume that high technol-
`ogy, high cost equipment will give a
`true and accurate representation of
`the original. Although hardware and
`software are improving all the time, it
`should be remembered this is not neces-
`sarily always the case. The data acqui-
`sition, however good and by whatever
`means, creates a discrete set of co-ordi-
`nates or data points and as such there
`will always be spaces between these
`points. Computer software, in the form
`
`BRITISH DENTAL JOURNAL VOLUME 205 NO. 7 OCT 11 2008
`
`391
`
`© 2008 Macmillan Publishers Limited. All rights reserved.
`
`

`

`GENERAL
`
`of reverse engineering packages such as
`Imageware, will then attempt to create
`a virtual best fit surface to those data
`points and as such the surface created
`cannot be absolutely accurate. However,
`advances in technology are enabling 3D
`images to be captured with suffi cient
`rapidity and precision that the clini-
`cal applications of such technology are
`surely set to increase further over the
`next few years.
`The authors would like to thank Mr Rupert
`Hoppenbrouwers of the DDU for his advice in
`the preparation of this manuscript and Hovick
`Boughosyan for his help with the images.
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