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3D CT imaging in orthodontics: adding a new dimension to diagnosis and treatment planning.



The use of lateral cephalometric radiographs forms an important diagnostic tool in orthodontic treatment as well as orthognathic surgery. However, their 2 dimensional nature presents an inherent limitation to the clinician, as the human body is 3 dimensional. In addition, a significant amount of radiographic radiographic (rā´dēōgraf´ik),
adj relating to the process of radiography, the finished product, or its use.
 projection error further limits their accuracy. Three-dimensional imaging of the human body via computed tomography has been available to the field of medicine for the last 30 years. However, the significant amount of radiation exposure associated with this technology, precluded its widespread use in dentistry. With the development of Cone Beam Computed Tomography, there has been a drastic reduction in radiation exposure to the patient, which allows its use for safely obtaining 3 dimensional images of the craniofacial craniofacial /cra·nio·fa·cial/ (kra?ne-o-fa´sh'l) pertaining to the cranium and the face.

cra·ni·o·fa·cial
adj.
Of or involving both the cranium and the face.
 structures. This should allow the clinician to visualize the hard and soft tissues of the craniofacial region from multiple perspectives, which could have far-reaching implications for treatment planning in orthodontics and orthognathic surgery. This paper shall discuss in detail the principles of the Cone Beam CT, and its applications in the field of orthodontics.

Introduction

Orthodontics is a field, which places a significant amount of emphasis on the modification of abnormal craniofacial growth patterns, in addition to the correction of dental malrelationships. Successful orthodontic and surgical treatment of such anomalies naturally requires efficient and reliable imaging of the structures of the cranial complex. Ever since the advent of the Bolton cephalometer cephalometer /ceph·a·lom·e·ter/ (sef?ah-lom´e-ter) an instrument for measuring the head; an orienting device for positioning the head for radiographic examination and measurement.

ceph·a·lom·e·ter
n.
 in 1931 (1), orthodontists have routinely used lateral cephalograms to aid in diagnosis and treatment planning, as well as evaluation of treatment. In addition, postero-anterior, panoramic, occlusal and peri-apical views of the skull and teeth have been used as and when required to aid in the diagnosis. All these additional radiographic views add up to a significant quantity of radiation exposure to the patient, which can and should be avoided if possible. Also, the 2 dimensional nature of these conventional radiographic views imposes further limitations such as overlap, leading to poor visualization of individual structures, errors due to projection, as well as the inability to identify true skeletal asymmetries when present (2). Thus, it has been recognized for some time now that three-dimensional imaging of the skull is the need of the hour in orthodontics.

3D Computed tomography in Orthodontics

Though three-dimensional computed tomography has been available to the medical profession for over 30 years now, the high radiation exposure and the prohibitive cost of this technology have till now precluded its use in orthodontics. However, recent advances in CT technology have seen a dramatic decrease in radiation as well as in cost, making it a viable and desirable alternative to traditional imaging. The new CT machines can perform a full scan of the head in a few seconds and give the patient an effective dose of only 50 micro-Sieverts, compared with about 2000 from a conventional CT scan of the whole head (3). This follows the ALARA principle (As low as reasonably acceptable) for radiation exposure, of the American Dental Association.

Radiation concerns are further reduced when one considers that a single CT scan can replace a number of conventional radiographs that are now considered essential for almost every orthodontic procedure. Thus, the routine use of CT scans for orthodontic diagnosis may not be very far away (4).

Cone Beam Computed Tomography (CBCT CBCT Cone Beam Computed Tomography
CBCT Catholic Bishops' Conference of Thailand
): Technique and Advantages

Conventional CT machines acquire image data by using either a single narrow X-ray beam or a thin broad fan-shaped X-ray beam. These X-ray beams rotate around the patient in a circular or spiral path as the patient moves through the scanning machine or as the rotating beam passes over the patient. A series of detectors register the attenuation Loss of signal power in a transmission.
Attenuation

The reduction in level of a transmitted quantity as a function of a parameter, usually distance. It is applied mainly to acoustic or electromagnetic waves and is expressed as the ratio of power densities.
 of these X rays, and from the data gathered, the machine reconstructs the internal structure of the patient's body (5). 3D data of the patient's anatomical structures is stored in the form of Voxels. These can be thought of as tiny cubes arranged next to each other. The brightness of each cube represents the density of the corresponding anatomic structure. Obtaining the final 3D object from the raw data requires a time consuming process called rendering, which is achieved using computer algorithms (6).

However, a new digital imaging breakthrough, the NewTom QR 9000 Volume Scanner (Verona, Italy) is now available for clinical practice. This CT scanner uses a cone-shaped X-ray beam that is large enough to encompass the region of interest. It produces a very focused beam, minimizing scatter, thus reducing the absorbed radiation dose to 45 microSieverts (7). In contrast to conventional CT imaging the patient remains stationary throughout the procedure. In a single scan, the X-ray source and a reciprocating X-ray sensor rotate around the patient's head and acquire 360 pictures (1 image per degree of rotation) in 17 seconds of exposure time. The 360 acquired images undergo a primary reconstruction to mathematically replicate the patient's anatomy into a single 3 dimensional volume. Further, the software allows for reformatting and viewing the image data from any point of view in all 3 dimensions. Thus, from a single scan, frontal, lateral, panoramic and other views can be created. Additionally, the anatomy can be peeled away layer by layer to locate the desired section. A major advantage of CBCT-generated cephalograms is the ability to excise unwanted structures such as the cervical spine and occiput, avoiding superimposition In graphics, superimposition is the placement of an image or video on top of an already-existing image or video, usually to add to the overall image effect, but also sometimes to conceal something (such as when a different face is superimposed over the original face in a  of irrelevant structures, and providing a remarkably clear image of pertinent maxillo-facial structures (8).

Uses of 3-dimensional computed tomography in Orthodontics

1. Assessment of alveolar bone

The alveolar bone height is particularly important in adults and periodontally compromised patients. Assessment of available bone is necessary prior to arch expansion or labial labial /la·bi·al/ (la´be-al)
1. pertaining to a lip or labium.

2. in dental anatomy, pertaining to the tooth surface that faces the lip.


la·bi·al
adj.
 movement of incisors. Surface irregularities due to ectopic ectopic /ec·top·ic/ (ek-top´ik)
1. pertaining to ectopia.

2. located away from normal position.

3. arising from an abnormal site or tissue.


ec·top·ic
adj.
 teeth, bone dehiscences, salivary gland invaginations and other abnormalities can also be visualized in three- dimensional images. A new resource for occlusal assessment is the lingual view-as if the clinician were looking from the back of the patient's head into the oral cavity.

2. Impacted tooth position

Impaction (or failure of eruption) of teeth is a common orthodontic problem, which requires precise localization Customizing software and documentation for a particular country. It includes the translation of menus and messages into the native spoken language as well as changes in the user interface to accommodate different alphabets and culture. See internationalization and l10n.  for the purpose of surgical exposure and guidance into the oral cavity. Conventional views such as the occlusal and periapical views cannot precisely locate such teeth. CT scans with 3 dimensional reconstructions provide an excellent means to accurately locate such teeth. In such a study done on a 21 year old girl, by V. Ravinder, Verma N and Valiathan A, at the Manipal College of Dental Sciences Links
  • MCODS WebLink
, Manipal (9), an impacted maxillary max·il·lar·y
adj.
Of or relating to a jaw or jawbone, especially the upper one.

n.
A maxillar; a jawbone.


maxillary (mak´siler´ē),
adj
 left canine was accurately localized, and revealed to be in a horizontal, palatal pal·a·tal
adj.
Palatine.


palatal (pal´t
 position. This was done, by obtaining various views, such as plain axial, sagittal sagittal /sag·it·tal/ (saj´i-t'l)
1. shaped like an arrow.

2. situated in the direction of the sagittal suture; said of an anteroposterior plane or section parallel to the median plane of the body.
 CT slices, as well as superior, sagittal and superior-oblique views of the maxillary dentition. Walker, Enciso and Mah (10) have also reported the advantages of 3D imaging in the management of impacted canines. In addition, cysts of the jaws, supernumeraries and ectopic/buried teeth can also be visualized using this technique.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

3. Temporomandibular Joint Assessment

Coronal cor·o·nal
adj.
1. Of or relating to a corona, especially of the head.

2. Of, relating to, or having the direction of the coronal suture or of the plane dividing the body into front and back portions.
, sagittal and axial views of the temporomandibular joint obtained from the CT scan can be correlated with the occlusal views. Functional shift of the joints can be occasionally detected as differences between the left and right TMJ TMJ
abbr.
temporomandibular joint syndrome


Temporomandibular joint pain (TMJ)
Pain and other symptoms affecting the head, jaw, and face that are caused when the jaw joints and muscles controlling them don't work
 views. In addition, 3D CT studies on patients who underwent orthognathic surgery, have allowed better evaluation of post surgical condylar con·dy·lar
adj.
Relating to a condyle.


condylar (kän´dilur),
adj pertaining to the mandibular condyle.

condylar axis,
n See axis, condylar.
 resorption resorption /re·sorp·tion/ (re-sorp´shun)
1. the lysis and assimilation of a substance, as of bone.

2. reabsorption.


re·sorp·tion
n.
 (11).

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

4. Surgical patients and those with syndromes and clefts

Surgical planning for patients with jaw asymmetry, e.g. Hemifacial Microsomia can benefit from 3 D imaging. This allows measurement of true jaw dimensions without the customary problems of magnification, superimposition and distortion, inherent in 2 D cephalograms. Use of virtual "cutting tools" and "collision tools" to plan out surgery on the 3D images, means that orthognathic surgery as well as distraction osteogenesis osteogenesis /os·teo·gen·e·sis/ (os?te-o-jen´e-sis) the formation of bone; the development of the bones.osteogenet´ic

osteogenesis imperfec´ta
 can be carried out with a far greater degree of precision, leading to more predictable results. (12) In patients with clefts, bone and soft tissue defects can be understood much better.

5. Facial Analysis

A conventional photograph is a simple two-dimensional representation that is not correlated with the supporting skeleton. The 3 D volume can provide any frontal, lateral or user-defined view of the face, and by changing the translucency of the image, one can determine the specific relationship of the soft tissues to the skeleton. This has significant implications in the planning of tooth movements, orthodontic extractions, orthognathic surgery, and other therapies that could alter facial appearance.

6. Tongue size and Posture

Volume measurements of the tongue could provide a more objective assessment of size, to aid in the diagnosis of open bites and arch-width discrepancies.

7. Airway assessment

Volume measurements of the airway could assess patency pa·ten·cy
n.
The state or quality of being open, expanded, or unblocked.



patency

the condition of being open.
, especially in patients suspected of mouth-breathing, adenoid hypertrophy or obstructive sleep apnea. Nasal morphology and turbinates can also be clearly seen in CT scans. This would mark a significant improvement over the use of 2 dimensional lateral cephalograms.

8. Root resorption

3 D CT images can show areas of root resorption on central and lateral incisors adjacent to impacted canine teeth. Walker, Enciso and Mah (10) showed that incisor incisor /in·ci·sor/ (I) (-si´zer)
1. adapted for cutting.

2. incisor tooth.


in·ci·sor
n.
 resorption adjacent to impacted canines is present in 66.7% of lateral incisors and 11.1 % of central incisors. A correlation was found between the proximity of impacted canines to the incisors and their resorption. Current CT machines may have too low resolution to detect early stages of root resorption as a result of orthodontic movement, but this may be possible in the future (6).

9. Planning for placement of dental implants

Osseo-integrated implants may be used in orthodontics either for the prosthetic replacement of missing teeth, or as stationary anchorage to facilitate tooth movement. Optimal spacing as well as correct root angulations of adjacent teeth must be achieved in order to successfully place dental implants (13). Cone beam CT scanning could be used to accurately assess space availability, root angulations, as well as the quality of alveolar bone at the implant site. This would replace the use of panoramic and peri-apical radiographs currently used for the purpose.

10. Cephalometric Analysis

Conventional 2D cephalometric measurements can also be carried out, by rendering a 2D projection of the 3 D data, resembling a radiograph radiograph /ra·dio·graph/ (-graf?) the film produced by radiography.

ra·di·o·graph
n.
. For bilateral landmarks, the computer can calculate the midpoint between them. Undoubtedly, new cephalometric landmarks and analyses based on 3 D data shall be developed in the near future.

Conclusion

3 dimensional computed tomography represents the cutting edge of orthodontic imaging and diagnostic capability. While mainstream orthodontists are still living and practicing in a 2 D world, orthodontic residents in many universities are becoming 3 D savvy. The several distinct advantages of 3D CT imaging, with ever-decreasing radiation doses, mean that this is where the future of orthodontic imaging lies.

Received 1 August 2007; published online 18 December 2007

References

(1.) Broadbent B.H. A new technique and its application to Orthodontia. Angle Orthod 1931; 1: 45-66.

(2.) Baumrind S. Integrated Three Dimensional Craniofacial Mapping: Background, Principles, and Perspectives. Semin Orthod 2001:7:223-232.

(3.) Mah J.K, Danforth R.A, Bumann A, Hatcher D. Radiation absorbed in maxillofacial imaging with a new dental computed tomography device. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003; 96: 508-13.

(4.) Hatcher D.C, Aboudara C.L. Diagnosis goes digital. Am J Orthod Dentofacial Orthop 2004; 125: 512-5.

(5.) Carlsson C. Imaging modalities in x-ray computerized tomography and in selected volume tomography. Phys Med Biol 1999; 44: 23-56.

(6.) Demetrios. J. Halazonetis. From 2-dimensional cephalograms to 3-dimensional computed tomography scans. Am J Orthod Dentofac Orthop 2005; 127:627-637.

(7.) Kau C.H, Richmond S, Palomo J.M, M.G. Hans. Three-dimensional cone beam computerized tomography in orthodontics. Journal of Orthodontics 2005;32:282-293.

(8.) Huang J.H, Bumann A, Mah J. Three-Dimensional radiographic analysis in orthodontics. J Clin Orthod 2005; 36; 7: 421-428.

(9.) V. Ravinder, Nikhar Anand Verma, Ashima Valiathan. 3-Dimensional Computed Tomography-A new method for localization of Impacted Canines. J Ind Orthod Soc 2002; 35: 73-75.

(10.) Walker L, Enciso R, Mah J. Three dimensional localization of maxillary canines with cone-beam computed tomography. Am J Orthod and Dentofacial Orthop 2005; 128: 418-423.

(11.) Bailey LJ, Cevidanes LH, Proffit WR. Stability and predictability of orthognathic surgery. Am J Orthod Dentofac Orthop 2004; 126:273-7.

(12.) Troulis M.J, Everett P, Seldin E.B, Kikinis R, Kaban L.B. Development of a three-dimensional planning system based on computed tomographic data. Int J Oral Maxillofac Surg 2002; 31:349-357

(13.) Ravinder V, James Sunny P, Mariette D'Souza, Valiathan Ashima. Osseo-integrated implants for maxillary lateral incisors- Orthodontic considerations. Malaysian Dental Journal 2003; 24(1):79-86.

Ashima Valiathan *, Siddharthan Dhar, Nikhar Verma

Department of Orthodonics and Dentofacial Orthopaedics, Manipal College of Dental Sciences, Manipal, Karnataka 576 104 India

* corresponding author e-mail: available@yahoo.com
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Author:Valiathan, Ashima; Dhar, Siddhartha; Verma, Nikhar
Publication:Trends in Biomaterials and Artificial Organs
Geographic Code:9INDI
Date:Jan 1, 2008
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