Review Article
`Three‑dimensional imaging techniques:
`A literature review
`Orhan Hakki Karatas1, Ebubekir Toy1
`
`Correspondence: Dr. Orhan Hakki Karatas
`Email: drorhanhakkikaratas@gmail.com
`
`ABSTRACT
`
`1Department of Orthodontics, Faculty of Dentistry,
`Inonu University, Malatya, Turkiye
`
`Imaging is one of the most important tools for orthodontists to evaluate and record size and form of craniofacial
`structures. Orthodontists routinely use 2‑dimensional (2D) static imaging techniques, but deepness of structures
`cannot be obtained and localized with 2D imaging. Three‑dimensional (3D) imaging has been developed in the early
`of 1990’s and has gained a precious place in dentistry, especially in orthodontics. The aims of this literature review
`are to summarize the current state of the 3D imaging techniques and to evaluate the applications in orthodontics.
`
`Key words: 3D imaging, 3D scanning, orthodontic diagnosis, treatment planning
`
`INTRODUCTION
`
`Over the years, orthodontic and dentofacial orthopedic
`diagnosis and treatment planning have relied essentially
`upon technological and mechanical supports such as
`imaging, jaw monitoring, and functional analyses. The
`goals of these techniques are to replicate or describe the
`anatomic and physiological facts exactly and to display
`the three‑dimensional (3D) anatomy precisely.[1]
`
`Imaging is one of the most important tools for
`orthodontists to evaluate and record size and form
`of craniofacial structures.[2] Orthodontists routinely
`use 2‑dimensional (2D) static imaging techniques
`to record the craniofacial anatomy, but deepness of
`structures cannot be obtained and localized with 2D
`imaging. 3D imaging has been developed in the early
`of 1990’s and has gained a precious place in dentistry,
`especially in orthodontics, and also in orofacial surgical
`applications. In 3D diagnostic imaging, a series of
`anatomical data is gathered using certain technological
`equipment, processed by a computer and later showed
`on a 2D monitor to present the illusion of deepness.[3]
`
`Facial soft and hard tissues and dentition are 3 main
`sections, also named as triad, in orthodontics and
`
`orthognatic surgery.[4] The triad has a significant
`function in planning of orthodontic treatment.
`Therefore, imaging of these structures is one of useful
`diagnostic tools for clinicians to make decision treatment
`modality.[5] 3D imaging for orthodontic purposes contain
`pre‑ and post‑treatment evaluation of dentoskeletal
`and craniofacial relationships and facial appearance
`and beauty, inspecting treatment results in terms of
`soft and underlying hard tissues, and 3D treatment
`predictions. 3D dental, facial, and skeletal records for
`making diagnostic decisions and planning treatment are
`the other benefits of using 3D imaging in orthodontics.[6]
`
`A large number of diagnostic methods have
`been developed to display facial structures and
`the dentition,[7‑9] most of which were abandoned
`due to their various drawbacks. The most
`popular method of current medicine is possibly
`3D imaging techniques giving detailed and
`problem‑oriented information about soft and hard
`tissues, such as Computerized Tomography (CT),
`Cone Beam Computerized Tomography (CBCT),
`Micro Computerized Tomography (MCT),
`3D laser scanning, structured light technique,
`sterophotogrametry or 3D surface imaging
`systems (3dMD), 3D facial morphometry (3DFM),
`
`How to cite this article: Karatas OH, Toy E. Three-dimensional imaging techniques: A literature review. Eur J Dent 2014;8:132-40.
`Copyright © 2014 Dental Investigations Society.
`
`DOI: 10.4103/1305-7456.126269
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`132132
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`Align EX1013
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`Tuned‑Aperture Computed Tomography (TACT),
`and Magnetic Resonance Imaging (MRI).[10‑17]
`
`The aims of this literature review are to present current
`state of the 3D imaging techniques and to evaluate the
`applications in orthodontics.
`
`HISTORICAL BACKGROUND
`
`In 1895, discovery of X‑rays by W. C. Roentgen
`opened a new era in medicine and dentistry.
`Thirty‑six years later, standardized methods for
`the production of cephalometric radiographs were
`introduced to the dental specialists by Broadbent and
`Hofrath simultaneously and independently,[18] and
`it remained comparatively unaltered until recently.
`Broadbent emphasized the importance of the position
`and distance arrangements to achieve distortion‑free
`radiographs when taking the lateral and posteroanterior
`cephalometric radiographs.[18] Cephalograms have
`been widely used in clinical implementations and
`as an investigation technique to evaluate growth
`and treatment responses. However, there are several
`disadvantages of 2‑dimensional cephalometry as a
`scientific method. The fact that a conventional head films
`reduce 3D objects to 2‑dimensional view is first and the
`most important reason. When 3D objects are displayed
`in a 2‑dimension, structures displace as vertically and
`horizontally in proportion to their distance from the
`film.[19,20] Secondly, cephalometric analyses are based on
`an excellent superimposition of the left and right sides
`at mid‑sagittal plane, but such superimposition is rarely
`observed because facial symmetry is infrequent. Third
`reason is that manual data collection and processing
`in cephalometric analysis have been shown to have
`low correctness and precision.[21] Finally, major errors
`in cephalometric measurements are associated with
`uncertainties in locating anatomical landmarks due to
`the deficiency of well‑defined outlines, hard edges, and
`shadows as well as patient position.[19]
`
`Beside these limitations, lots of cephalometric analyses
`have been developed to help diagnose skeletal and
`dental malocclusions and dentofacial deformities.[22,23]
`The quantitative errors associated with traditional 2D
`cephalometry have been substantial enough to make
`orthodontic diagnosis and treatment planning.[19,22‑28]
`
`Following the introduction of 3D imaging, clinicians
`have had great opportunity to evaluate anatomic
`structures 3‑dimensionally in orthodontic practice.
`Several investigators conducted 3D imaging
`researches, and Singh and Savara[29] reported the
`
`first 3D analysis about growth changes in maxilla.
`Computer softwares helped to collect and analyze
`3D coordinates directly from digital cephalometric
`images, so that tracing manually and digitizing with
`mouse on screen were abandoned.[30,31]
`
`3D imaging technique has been improved to
`use in different areas of health sciences. Being
`improved old photogrammetric techniques,
`stereophotogrammetry has been introduced to
`provide a more extensive and accurate assessments
`of the captured things. Using one or more converging
`pairs of views, a 3D model can be constructed and
`monitored from any perspectives and measured
`from any directions. In 1944, Thalmann‑Degan
`recorded facial differences after orthodontic
`treatment. This was the earliest clinical report
`about stereophotogrammetry.[21] Computerized
`stereophotogrammetry has come into market
`as parallel to computer developments and has
`provided faster, more comprehensive and correct
`taking and constructing sequences.[32]
`
`The first CT scanning device was developed around
`40 years ago. After a short time, a stack of CT sectional
`images was used to obtain 3D information. At the
`beginning of 1980s, clinicians used 3D imaging in
`craniofacial deformities. For craniofacial surgical
`needs, first simulation software was introduced
`in 1986. Then, the principles and applications of
`3D CT‑ and MRI‑based imaging in medicine were
`published. A specific discipline was established on
`3D imaging, dealing with different types of imaging,
`manipulation, and analysis of multi‑dimensional
`medical structures.[32]
`
`3D IMAGING METHODS
`
`Computed tomography (CT)
`CT imaging, also called computerized axial
`tomography (CAT) imaging, uses special X‑ray
`equipment to generate cross‑sectional images of the
`body.
`
`CT devices are divided into 2 groups: Cone beam and
`fan beam.[33] Using conventional fan beam CT devices,
`the X‑ray source and detectors with the circular metal
`frame rotate around the patient. Patients are placed
`in a horizontal position on a table when CT scanner
`works. The table slowly passes through the center of
`a large X‑ray machine. The procedure causes no pain,
`but some tests require a contrast material to make
`some parts of body appear better in the image.
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`CT scanner works as follows:
`The patient is moved into circular opening of the CT
`imaging by a motorized table. When the patient is
`ready, the operator starts the CT imaging system, and
`a complete rotation of X‑ray source and detector lasts
`about 1 second. The CT device generates a narrow,
`fan‑shaped beam of X‑rays scanning a section of the
`patient’s body. A “snapshot” image was recorded and
`collected by a detector opposite from the X‑ray source.
`The obtained data are transmitted to a computer
`for each turn of the scanner and detector. One or
`multiple cross‑sectional images of the body parts were
`reconstructed.
`
`The patient is usually scanned in the axial plane
`sections taken in succession; the desired image appears
`when these sections combined. CT can achieve 64
`and/or 128 sections in advanced fan beam CT at a
`one time. The system is most expensive because the
`image is obtained by increasing number of sensors.
`However, this system can perform in less time and
`at a low dose shooting.[33] In this technique, due to
`the sectioning of tissues, organs are not superposed
`on each other.
`
`Although CT scans are very high‑priced and have high
`radiation dose to be suitable for a lot of orthodontic
`applications, the benefits outweigh the risks in certain
`situations. For example, treatment of craniofacial
`deformities may be insufficient with 2‑dimensional
`diagnostic records. CT scans generate a very intensive
`data set that contains 3D information about soft and
`hard tissues. These data may be extremely precious
`for diagnostic point of view.
`
`In addition, the usage area of CT is quite wide in
`dentistry, such as in the diagnosis of some pathologies,
`and even the contents of the boundaries (solid,
`liquid, Agar‑Agar) in determining the salivary gland
`pathologies,[34] examination of the structure of the
`temporomandibular joint (TMJ),[35] TMJ ankylosis or
`fractures,[35] examination of the maxillary sinus,[36]
`orofacial trauma and fractures,[37] differences in airway
`volumes after rapid palatal expansion,[38] and implant
`applications.[39]
`
`Some disadvantages of CT are:
`• Expensive,
`• Not available in every hospital,
`• Skips lesions far away from the sections,
`• Foreign objects like restoration and prosthetics
`create artifacts,
`In addition, CT data is insufficient compared with
`other soft‑tissue imaging techniques.[40]
`
`•
`
`Cone beam computerized tomography (CBCT)
`Craniofacial CBCT devices [Figure 1] are designed to
`overcome some of the limitations of conventional CT
`scanning devices.[41] There are a lot of differences among
`the CBCT devices including patient positioning, scan
`time, resolution, radiation dose, and clinical ease of use
`of cross‑sectional area.[42] In addition, while some CBCT
`devices scan all head area, others scan only the chin area.
`
`With the cone‑beam systems, dental therapists can
`achieve 3D (volumetric) data with very low radiation
`dose at one time.[43] At the same time, CBCT allows
`re‑alignment of 2‑dimensional images in coronal,
`sagittal, oblique, and various incline planes [Figure 2].
`When we compare CBCT with CT, patients’ visualization
`with less radiation dose is possible.[42,44] CBCT devices
`provide 15 times less radiation dose than conventional
`CT scanners do. The radiation dose of CBCT equals to
`a dose of average 12 panoramic radiographs.[11]
`
`Figure 1: Cone beam computerized tomography for craniofacial
`imaging
`
`Figure 2: CBCT images of craniofacial structure obtained from various
`incline planes
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`In orthodontics, craniofacial images obtained with
`CBCT devices provide important information in
`different categories. Complex relation between
`treatment, development, and craniofacial data can
`be explained or data can be used as an independent
`solution for one and more of the following categories:[40]
`• Determination of normal and abnormal anatomy
`• Making decision on root length and alignment
`Jaw size and distance of examined teeth
`•
`• Determination of relationship between jaw size
`and examined teeth size
`• Determination of 3D maxillo‑mandibular
`relationship
`• Determination of the status of the TMJ
`• Determination of the effects of orthodontic
`treatment in craniofacial anatomy
`• Detection and localization of impacted or
`supernumerary teeth.
`
`The ability of providing 3D images of craniofacial
`structures with minimum amount of distortion has
`increased the availability of this technology.[11,40]
`
`Advantages of CBCT in orthodontics
`a. Cost: CBCT devices have gained smaller size,
`thanks to technological developments. The
`cost of CBCT imaging is very low compared to
`computerized tomography. Image processing is
`easier because it is limited to the head and face.
`Maintenance cost of CBCT devices is much less
`b. Reduction of radiation dose: Referring to the results
`of the different studies, CBCT devices emit up to
`98% less radiation. CBCT devices emit on average
`36.9‑50.3 microsievert (μSv) of radiation dose: On
`average, 1.320 to 3.324‑μSv for the mandible and
`1.031 to 1.420 μSv for maxilla
`c. Quick scan: With CBCT devices, all raw data are
`obtained in a single turn. In this way, the patient’s
`length of stay is reduced and the device increases
`patient satisfaction
`d. Dimensional reconstruction feature: The most
`important advantage of CBCT is possible to display
`and arrange 3D data in personal computers
`e. Image processing: Various comprehensive
`softwares for implant placement and orthodontic
`measurements are available.
`
`Disadvantages of CBCT in orthodontics
`Cone beam geometry, sensor sensitivity, and contrast
`resolutions as well as some other limitations lead to
`some disadvantages in the CBCT technique:
`a. The main factor of weakness in image quality
`is image artifacts, such as metal brackets and
`restorations.
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`
`b. The actual color of the skin and soft tissue images
`cannot be determined.[11]
`c. Unwanted patient movement may cause image
`disorder.
`d. Price of these devices is more expensive than
`conventional X‑ray equipment, and these devices
`require more space.
`e. Radiation scattering may occur preventing of
`image monitoring.
`
`CBCT has not only relatively limited capacity in
`displaying soft tissues, but also has an arguably
`place for investigation of hard tissue of the head
`and face.
`
`CBCT in orthodontic application
`Impacted teeth and intraoral anomalies
`In determining position of the ectopic cuspids
`accurately, CBCT can be used for the establishment
`of therapeutic strategies to employ minimal invasive
`surgery.[45] Although the pathologies created by
`ectopic teeth and surrounding structures can be
`identified with conventional radiograph, the studies
`being conducted with CBCT scans give more accurate
`data regarding the actual relationships between
`impacted teeth and adjacent teeth, and possible root
`resorptions [Figure 2].[46]
`
`Another application area of CBCT is to determine the
`position of oral abnormalities in patients. Previous
`studies showed that after using the CBCT, incidence
`of oral abnormalities has increased compared to the
`earlier studies.[45,47]
`
`The nasopharyngeal airway analysis
`CBCT technology has caused great progress in the
`nasopharyngeal airway analysis. While enlarging the
`airway is not a direct goal of orthodontic treatment,
`CBCT and lateral cephalographs are widely used for
`airway measurements. As a result, either surgical
`removal of the adenoids/tonsils or obstructive sleep
`apnea therapy due to narrow airways can be applied
`if necessary.
`
`The potency of CBCT to measure airway volumes has
`helped orthodontists for studying in airway volume
`differences as a result of rapid palatal expansion[48]
`and premolar extraction.[49] In both studies, airways
`were found to be unchanged after orthodontic
`treatment.
`
`In another study using lateral cephalograms and CBCT,
`there was a moderate difference in upper airway area
`and volume measurements of 11 patients.[33]
`
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`

`Cleft lip⁄palate patients
`Among different patient groups, CBCT is more
`important for individuals with congenital
`malformations.[50] Since the prevalence of cleft lip/
`palate (CL/P) is very high in population,[51,52] it is
`not unexpected that researches on CBCT imaging
`in orofacial deformities have concentrated on these
`patients. Since CBCT use in CL/P patients was found
`efficient in early clinical cases,[53] a great number of
`researchers estimated the alveolar cleft volume to assist
`pre‑alveolar graft surgery.[54,55] The proper amount of
`graft material can be prepared via CBCT volumetric
`analyses to assure enough alveolar bone in CL/P
`patients. In addition, CBCT is also used for soft tissue
`evaluation of CL/P patients pre‑ and post‑operatively.
`
`Both conventional radiographs and CBCT imaging
`are principally used to assess mineralized tissues.
`Differences of nasal and labial tissues between the
`age‑matched non‑CL/P patients and CL/P patients
`without synchronous rhinoplasty and the CL/P
`patients with synchronous rhinoplasty were examined
`using CBCT. Nasal reconstruction conducted
`during primary lip repair is named as synchronous
`rhinoplasty. Based upon differences in soft tissue
`measurements from CBCT images among 3 groups,
`synchronous rhinoplasty is suggested to optimize
`nasal and labial appearance in CL/P patients.[56]
`
`Temporomandibular joint (TMJ) morphology
`Condylar head size, shape and position, the joint space
`can be evaluated in CBCT. The condyle is viewed
`from only lateral side in lateral cephalometric films,
`but with CBCT, frontal and axial cross‑sections can be
`displayed. However, since CBCT is not sufficient to
`view the soft tissues, examination of disk structures
`in TMJ is difficult.[57]
`
`CBCT image analyses
`The front or profile photos can be converted to
`DICOM (Digital Imaging and Communications in
`Medicine) database with a new software programs.
`3‑dimensional view of the face can be created in any
`desired direction. Changing the image transparency,
`anatomic relationships between the hard and soft
`tissues can be defined. Changes in the appearance of
`the face after tooth movement, orthognathic surgery or
`other craniofacial treatment can be detected with CBCT
`image. In addition, models of images obtained from
`CBCT can be prepared with 3D Fotoscan devices.[58]
`
`Three‑dimensional superposition
`Images of cranial structures taken at different times
`can be superimposed on pre‑defined points using the
`
`136
`
`3‑dimensional software. Measurements performed on
`these images are imported to a computer, and then
`growth changes and treatment progress are evaluated.
`Thus, stability and post‑treatment assessment can be
`made with the help of 3D superposition.[58]
`
`In addition, CBCT provides information about
`root inclination and torque, bone thickness and
`morphology at the points where mini‑screws are
`decided to be implanted and osteotomy sites during
`surgical planning.[59]
`
`The positions of the mandibular and maxillary incisor
`roots, the amount of bone in the posterior maxilla for
`distalization, the amount of bone available for the
`maxillary buccal segments for dental expansions,
`neighborhood between maxillary sinus and maxillary
`teeth roots can be examined before and after selected
`treatment procedure.[60]
`
`Micro‑computed tomography (MCT)
`MCT is substantially the same as CT except that the
`reconstructed cross‑sections are bounded to a much
`minor area [Figure 3]. 0.012 mm thin cross‑sections
`can be taken with conventional CT, but MCT can
`be obtained with the nano‑sized sections. MCT, a
`non‑invasive and a non‑destructive technique, is used
`for the analysis of mineralized tissues. The future of
`MCT lies in its capacity to sample input over a much
`minor volume than full body, considerably reducing
`the radiation exposure.
`
`With the use of modern technology at X‑ray sources
`and detectors, MCT devices have 10,000 times more
`resolution than medical CT scanners do.[61] The system
`has a micro focus X‑ray source, a CCD camera, and a
`personal computer for control of the system. The X‑ray
`radiation source with focal spot size of 10 mm is used to
`scan the objects. CCD camera provides high‑resolution
`images. MCT gives important information about
`wound healing and micro vascular researches in
`orthopedics. The MCT devices are also used in
`researches related to endodontics, prosthetics, TMJ,
`and dental caries.[62,63] Current MCT scanning of bone
`has revealed accurate and precise information about
`
`Figure 3: Micro‑computed tomography for analysis of mineralized
`tissues with micro‑sized sections
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`bone stereology and micro architecture. This method
`has been used clinically to evaluate osteoblastic/
`osteoclastic alveolar remodeling as well as bone
`dehiscence and root resorption in orthodontics.[64,65]
`Osseo‑integrated implants used for orthodontic
`anchorage can be evaluated with MCT.
`
`3D laser scanning
`As a less invasive method of capturing the face, laser
`scanning supplies 3D images for treatment planning
`or evaluating effects of orthodontic and especially
`orthognathic treatment. In addition, the 3D laser
`scanners can produce digital models.
`
` However, this technique has several disadvantages
`for 3D scanning. For example:
`• Procedure is so slow that distortion occurs on the
`scanned image
`• While the scanner revolves around the patient’s
`head, the patients should stay motionless for one
`minute or longer. Due to the potential patient
`movement and security issues related to laser,
`intraoral laser scanning is very difficult to obtain
`digital models[41]
`• Safety issues are important, such as exposing eyes
`to the laser beam, particularly in growing children
`• There is an inability to capture soft tissue surface
`texture, which results in difficulties in identification
`of landmarks due to surface color.[22]
`
`Structured light technique
`Because much of what is diagnosed in facial aesthetics
`need to be related to the deeper structures of bone and
`muscle, it can be feasible to investigate the face at its
`surface level only. Structured light scanning enables
`the 3‑dimensional shape of the face in a simple way
`and without ionizing radiation. The result is a 3D
`shape of the patient’s face, viewable on a computer
`screen.[66] 3D facial analyses are accessible now, and 3D
`superimposition disclosing treatment effects would
`come into use. The image is illuminated by the light,
`and taking a single image is sufficient in structured
`light technique.
`
`The position of illuminated points in obtained image
`is necessary for 3D reconstruction of the object.[67]
`The main aim of this technique is to combine the
`facial shape and underlying radiographic data from
`other sources to conclude 3D structures for diagnosis,
`treatment goal, and evaluation of treatment results.
`Also, 3‑dimensional images of the teeth can be obtained
`using the structured light technique in the mouth.
`However, to obtain high‑concentration samples, the
`
`face needs to be illuminated a few times with random
`patterns of light.[68] This rises the capture time with
`increased probability of head action. In addition,
`the use of one imager does not assure an 180o (ear to
`ear) facial model, which is not convenient and has
`resulted in decreased applicability of this technique.[69]
`Structured light technique can be used to determine
`the position of the brackets correctly. Ora‑Scanner (the
`first 3D hand‑held intra‑oral scanner) is based on
`structured light techniques. In this system, white light
`is used. Techalertpaisan and Kuroda[70] used 2 LCD
`projectors, a camera and a computer, to produce 3D
`image of face shape that may be altered, moved, or
`revolved lightly in all directions. This system requires
`at least 2 seconds to capture an image, which may be
`too long in avoiding the movements of babies and
`children. Another kind of structured light technique
`was presented by Curry et al.[71] This system has got
`2 cameras and 1 projector. Hue coded light figure is
`projected on the face before obtaining every image.
`The displacement of the pattern enables the software
`to evaluate an accurate 3D model. Structured light
`figure, when united with stereophotogrammetry to
`measure the light figure precisely, ends up with the
`generation of an accurate 3D plan.
`
`Sterophotogrametry
`Stereophotogrammetry includes photographing a 3D
`object from 2 different coplanar planes in order to
`acquire a 3D reconstruction of the images [Figure 4].
`This technique has proven to be very effective in
`the face display. It mentions to the private case
`with 2 cameras, arranged as a steropair, are used
`to recover 3D distances of features on the surface
`of the face.[72] The technique has been implemented
`clinically by using a mobile stereometric camera.[21]
`Contemporary stereophotogrammetry may be used
`to clear up accurate 3D skull mapping. In 1944, the
`
`Figure 4: Stereophotogrammetry with 2 different coplanar planes for
`3D images
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`first clinical use of stereo photogrammetry applied
`by Thalmann‑Degan and recorded the changes
`that occur on the face of the patients as a result of
`orthodontic treatments.[21] Ras et al.[15] have developed
`a stereophotorammetric system that presents the 3D
`coordinates of any chosen facial landmarks. This
`system includes 2 synchronized semi‑metric cameras
`installed on an outline with distance of 50 cm between
`them and located convergent with an angle of 15.[73]
`
`Due to tissue reflections, hair and eyebrows
`intervention, change of posture between the different
`views and movements during imaging decrease the
`probability of obtaining the most accurate facial
`images. In addition, since laser or light cannot
`penetrate to excessively curved and reflective surfaces,
`certain structures, such as the eyes and ears, cannot
`give a good image.
`
`3D facial morphometry (3DFM)
`3D Facial Morphometry may be used in clinics
`after capturing the subject as a supplement to the
`cephalometric analyses. The system consists of 2
`infrared cameras, a hardware for the recognition
`of markers and a software for the 3D rebuilding
`of landmarks’ coordinates.[16] Landmarks are
`positioned on the face and later covered with 2 mm
`semi‑spherical reflective markers. An ultraviolet
`stroboscope is used to light up the projective markers.
`Two‑ sides’ determination is generally needed to
`acquire the whole face. Placement of landmarks on
`the face is labor‑consuming and takes very long
`time. Repeatability of the landmarks determination
`is very difficult and questionable. Changes of facial
`statement between two achievement periods enhance
`size of error. This system cannot produce models
`to display the natural soft‑tissue appearance of the
`face expression. In conclusion, it is not wise to use
`this system as equipment for making decisions
`on orthodontic treatment, and for communication
`between patients and orthodontists or surgeons.
`
`Tuned‑aperture computer tomography (TACT)
`There are many shortcomings of current radiologic
`techniques. In 1990, the National Institute of Dental
`Research decided to support the improvement
`of a system for manufacturing 3D images
`tomosynthetically from a device including a
`multi‑tube X‑ray and X‑ray charge‑coupled device
`screen. The most comprehensive result of this
`effort is TACT system that may alter multiple 3D
`pictures.[74] Tuned‑Aperture Computed Tomography
`or TACT (Wake Forest University, School of Medicine,
`
`Winston‑Salem, North Caroline, USA) is developed by
`Richard Webber.[1] TACT is a low‑dose 3‑dimensional
`imaging system. A calibration or reference marker in
`the area of view to permit for synthetic reconstruction
`of the desired image plane is placed by the TACT
`technique. However, it does not meet the need for
`accurate control and information of the imaging
`geometry. The object and image sensor must be
`remain fixed in this technique, and the position of the
`X‑ray source can be elective. The calibration marker
`permits to decide on the imaging geometry used to
`exhibit the absolute imaging from the final result
`image. This technique allows the processing of all
`resultant images into 3D volume. In fact, this method
`is used in medicine, but it can be used in the dentistry
`as well. The uses of TACT for dental purposes have
`been shown in several studies. TACT seems to have a
`greater diagnostic value in its ability to detect dental
`caries, impacted teeth, and to evaluate pre‑implant
`images.[75] The future of TACT for orthodontics lies
`in its ability in evaluation of dento‑alveolar bone
`volume, detection of root resorption, and evaluation
`of the TMJ disorders.[76]
`
`Magnetic resonance imaging (MRI)
`MRI operates by achieving a resonance signal from the
`hydrogen nucleus. Therefore, it is basically imaging of
`water in the tissue. MRI method is the highest contrast
`resolution medical imaging technique. Radio waves are
`sent to desired location for examination in a magnetic
`field. The energy produced from hydrogen atoms in
`the cells stimulated by radio waves are converted to
`numbers; they are processed on a computer and then
`converted to image. MRI is very convenient for the
`study of skeletal physiology, tumors, and the healing
`of grafts. Although MRI technique has a shorter
`history in the TMJ investigation, it is considered to
`be the gold standard for imaging of the TMJ.[77] If one
`needs detailed information about the intracapsular
`joint effusion, joint pain, and adhesion and perforation
`of articular disc, MRI is a preferred choice. The
`information provided by MRI, condylar erosion,
`osteopathy, and the determination of the position of
`the disk is successful in about 90%.[78]
`
`Advantages of MRI in orthodontics:
`1. It gives very valuable information about the position
`and morphology of disk and excellent soft‑tissue
`resolution with radiation‑free imaging technique
`2. Based on the changes in the signal intensities, it
`can also display detailed osseous tissues
`3. It can be safely used in patients who are allergic
`to the contrast agent
`
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`European Journal of Dentistry, Vol 8 / Issue 1 / Jan-Mar 2014
`
`Karatas and Toy: Three‑dimensional imaging
`
`

`

`4. The images can be obtained without repositioning
`the patient
`5. I t also provides opportunity to examine
`inflammatory processes and scar tissues.
`
`Disadvantages of MRI:
`1. It requires expensive and advanced equipment
`2. Unavailability in every medical center and dental
`office
`3. It takes a long time to use in TMJ
`4. It is contraindicated in the patients with
`claustrophobia.[27]
`
`Stainless steel and other metals used in orthodontic
`brackets were shown to produce artifacts.[79] Therefore,
`patients undergoing orthodontic treatment should be
`carefully evaluated for MRI needs.
`
`CONCLUSIONS
`
`Need for high speed, high density, small size, and
`multifunctional device has driven the development
`of 3D imaging. New imaging techniques require
`expensive software and a lot of time to operate them.
`The future of 3D imaging seems to be faster and more
`flexible robotic devices.
`
`REFERENCES
`
`4.
`
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`2. Ucar FI, Sekerci AE, Uysal T, Bengi AO. Standardization of records in
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`3. Hajeer MY, Millett DT, Ayoub AF, Siebert JP. Applications of 3D
`imaging in orthodontics: Part 1. J Orthod 2004;31:62‑70.
`Plooij JM, Maal TJ, Haers P, Borstlap WA, Kuijpers‑Jagtman AM, Bergé
`SJ. Digital three‑dimensional