Cone Beam Computed Tomography in theAssessment of Dental ImpactionsDa

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modental profession, the dentists access to ad-vanced imaging has become facilitated while sig-nificantly lowering the radiation dose to the pa-tient, as complicated diagnostic challenges were

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DiaE-mth is usually done using the buccal objectle, as well as taking two radiographic imagesright angles to one another, usually a peri-ical and an occlusal view.1 Diagnosis andatment planning is often confounded withe presence of one or more impacted teeth atusual relationships to the erupted denti-n, as well as important anatomical land-

often sent for medical CT evaluation in the past.CBCT can show the location of the impactedteeth, as well as their relationship and effect onthe surrounding dentition, and the data ac-quired during imaging can be reformatted toshow sequential slices through the oral and max-illofacial complex in the axial, coronal, and sag-ittal planes. These same data can further bemanipulated to produce 3D reconstructions ofthe area of interest, giving the dentist a clearerpicture of the exact location and behavior of theteeth in question. 3D reconstruction helps elim-inate the confusion often encountered when at-tempting to view teeth in each of the threeanatomical planes, an exercise not usually in-cluded in traditional dental training. In addi-tion, panoramic reconstruction of the data canbe performed to give the dentist a more familiarradiographic image to evaluate without the pres-

From 3D Diagnostix, Brighton, MA.Conflict of interest: Dr. Tamimi is a consultant for 3D Diag-tix, who provided the 3D reconstructions of the examples used inarticle. Mr. ElSaid is the president of 3D Diagnostix.Address correspondence to Dania Tamimi, BDS, DMSc, 3Dgnostix, 167 Corey Road, Suite 111, Brighton, MA 02135.ail: drtamimi@3ddx.com 2009 Elsevier Inc. All rights reserved.1073-8746/09/1501-0$30.00/0doi:10.1053/j.sodo.2008.09.007

57Seminars in Orthodontics, Vol 15, No 1 (March), 2009: pp 57-62nia Tamimi and Khaled ElSaid

Radiographic interpretation and diagnoassociated pathology have long posedimpactions can occur due to pathologwhich can be evaluated more accurateraphy (CBCT) imaging. Three-dimensioand determination of the type of immultiplanar reformats of the CBCT datstruction to give the clinician a sense oand their relationship to their adjacentplanning for extraction, the location oaccurately. The advent of CBCT has bethe diagnostic options and capabilitiefull utilization of its many options cantreatment planning tool. (Semin OrthoAll rights reserved.

adiographic interpretation and diagnosisof dental impactions and different asso-

ted pathology have long posed a challengethe clinician. Plain film radiography offersof dental impactions and differentchallenge to the clinician. Dentalr developmental factors, both ofing cone beam computed tomog-ocalization of the impacted teethion can be performed using thewell as three-dimensional recon-

e position of the teeth in the boneuctures, In the event of treatmenttal structures can be determinedmonumental event for improvingthe orthodontist. Familiarity andovide the dentist with a valuable009;15:57-62.) 2009 Elsevier Inc.

rks that must be evaluated should extrac-n or other surgery be considered.With the advent of cone beam computed to-graphy (CBCT) and its widespread use in the

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58 D. Tamimi and K. ElSaidion usually associated with conventional pan-amic imaging.For 3D reconstruction, CT images are con-ted from axial slices into a 3D image using aies of steps. The first step is called threshold-, where a Hounsfield range (grayscale mea-red in Hounsfield units [HU]) of the desiredatomy is specified. For example, if one is seg-nting the mandible, a threshold between 300and 1800 HU is selected. This thresholding

eration will exclude soft tissue and air fromimages. The resulting segmentation will con-

n some artifact due to scatter from metal ob-ts and fillings. This artifact is cleaned in thext step, manual cleanup, where the operatores through the images one by one, cuttingay the artifact and extraneous objects fromimages. Region growing is the third step,

ere the operator selects a seed point withinstructure of interest that has been alreadymented in the first two steps. That seed pointl grow into the complete region of interestOI). For example, region growing for thendible will usually remove the spine from themented mask. Finally, the resulting segmen-ion of the individual slice is combined to-ther by interpretation creating a 3D recon-uction.2 Examples of these images are shownthis article.

termining the Etiology for Dentalpaction

paction implies the failure of the tooth topt into the oral cavity after development of

e roots is complete (closure of the apices). Ath with open apices is considered une-pted until the root is fully developed. Care-l radiographic examination can determinee stage of development, and may deem anerupted tooth likely to become impacted iforientation of its long axis does not lie in the

th of eruption.Dental impactions can occur due to two fac-s: (1) pathological, such as a tumor, cyst, oral or systemic bone pathology that increasese density of bone that can displace or im-de the eruption of the tooth, and (2) devel-mental, such as jaw size, eruption pattern ofteeth, supernumerary teeth, or ankylosis. De-mining the reason for the impaction greatlysurgery may be included in the treatmentn before the commencement of orthodonticatment.

thological Factors

e of the radiologic hallmarks of cysts and be-n tumors is the displacement of teeth. To im-de eruption, the lesion should be located coro-l to the tooth. The most common odontogenicors are odontomes, and 70% of them are as-iated with abnormalities such as impaction,lpositioning, diastema, aplasia, malformation,d devitalization of adjacent teeth.1 Benign cystsd tumors that have been known to cause impac-n include dentigerous cysts, odontogenic ker-cysts (OKC), ameloblastomas, calcifying epithe-l odontogenic cysts (CEOT), and adenomatoidontogenic tumors (AOT).1 Also, diseases ofne that increase the density of the bone sur-nding the tooth may cause impaction, such asrous dysplasia, and syndromes associated withltiple supernumerary teeth such as Gardnersdrome can show impaction of these teeth.1,3

CT evaluation of impacted teeth due to suchions can help in localization of these teeth, asll as assessment of the extent of change/destruc-n to the surrounding structures (Fig 1).

velopmental Factors

e teeth most commonly impacted, after therd molars, are the maxillary canines. The in-ence of maxillary ectopic canines occurs inproximately 3% of the population. The distri-tion and location has been reported at 80%latally and 20% buccally. These teeth are of-crowded out of the arch as they have thegest period of development, follow the mostbious course in their eruption, and occupyeral developmental positions in succession.e size of the jaw and length of the arch deter-ne how much space the dentition has to alignelf into occlusion.4 The tube shift methodso known as the parallax technique) has beentraditional method of locating these canines

d provides an arbitrary position and approxima-n of the level of difficulty for the managementthe canine. This investigative technique uses twonventional radiographs and the location of theth identified by the movement of the objectspectively to the way in which the radiograph was

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59Assessment of Dental Impactionsen. In addition, the extent of the pathologysed by the ectopic tooth and its surroundinguctures has also been evaluated by these radio-phs.5,6 A recent report found that the use ofCT technology could add value to the manage-nt of patients with such anomalies.7 The au-rs used the technology to precisely locate theopic canines and to design treatment strategiest allowed for minimally invasive surgery to berformed and helped to design effective orth-ontic strategies (Fig 2).The presence of supernumerary teeth, sucha mesiodens or a fourth molar, may or mayt be associated with impaction of the teeth,pending on the arch length and alignment ofrest of the dentition. The most common sitesingle supernumerary teeth is in the maxil-

y incisor area, and multiple supernumeraryth occur most frequently in the premolarion, usually in the mandible.1 CBCT can helplocalization of these supernumerary teeth ination to the surrounding teeth and other struc-es by reformatting the data acquired in theee anatomical planes and examining the teeththese planes, giving the diagnostic process theded advantage of buccolingual evaluation ofch individual section without superimposition ofadjacent teeth and structures (Fig 3).Another reason for impaction is ankylosis,ich is characterized radiographically by a dis-

re 1. Multiplanar reformats in the (A) axial,coronal, and (C) sagittal planes of a third molaracted due to a dentigerous cyst.theforlarteereginrelturthrinadeathe

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60 D. Tamimi and K. ElSaidntinuity of the PDL space surrounding theth, thus creating an inflexible tooth-to-bonentact causing the tooth to become impactedsubmerged.3 CBCT imaging can aid in evalu-on of the orientation of the tooth and itsation and effect on the surrounding struc-es (Fig 4), as well as its position in relation toclusion if the images are taken with the teethly occluded. Actual lamina dura evaluationy be more accurate using periapical radiogra-y, as the evaluation of fine bone detail mayt be optimal using CBCT.

pes of Impaction

pactions are usually evaluated by examiningangle of the long axis of the tooth. A tooth

ose long axis lies in the horizontal or verticalne is called horizontally or vertically im-cted respectively (Figs 2 and 5). If the longis is tilted with the crown closer to the midlinethe jaw than the root apex, it is mesioangu-ly impacted. Conversely, if the crown is fur-er from the midline than the apex, it isistoangularly impacted. A horizontally im-cted tooth may be oriented in a manner thatgns the axis of the tooth at a right angle to thentition (ie, faciolingually), and any of thesees of impactions can have a buccolingual tiltig 6). Evaluation of these teeth is complicated

ure 2. Superior view of a three-dimensional recon-uction of the maxilla with the bone digitally re-ved to show the position of the horizontally im-cted right maxillary canine and vertically impactedt maxillary canine in relation to the erupted denti-n. (Color version of figure is available online)use of advanced imaging (CBCT). This im-ing modality can provide a spatial picture inee dimensions for the clinician to accuratelyess and plan treatment. 3D reconstruction oforal and maxillofacial complex can further aidevaluation by eliminating the guesswork, anding the clinician a clear visual aid for the posi-n of the teeth in relation to their supportinguctures. In the case of mixed dentition, theimary teeth can be digitally removed to evaluateunerupted permanent dentition (Fig 3).

ure 3. (A) Axial view showing the position of arizontally impacted left mesiodens and cross-sec-n through a vertically impacted right mesiodens.) Three-dimensional reconstruction of the dataws the superior view of the same case. The boned primary teeth were removed digitally to showposition of the unerupted permanent teeth

m the superior aspect. Note the open apices ofdeveloping permanent dentition. (Color ver-

n of figure is available online)

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61Assessment of Dental Impactionsfect of Impacted Teeth onrrounding Structures

e impacted tooth may displace, impede theption, and/or cause external resorption ofadjacent teeth. Clinical reports using 3D

nventional CT scans have shown that the inci-nce of root resorption to the adjacent teeths been greater than previously thought.8 If thepacted tooth is partially erupted, it may act asplaque trap facilitating the development ofries in both it and the adjacent tooth. If theth is in contact with the buccal or lingualrtices of the jaw, it may cause thinning orht expansion corresponding to the anatomythe tooth and its follicle.

ure 4. Three-dimensional reconstruction show-impaction of a right second molar due to anky-

is and its relationship to the inferior alveolarrve. (Color version of figure is available online)

ure 5. Frontal view of a three-dimensional recon-uction of the mandible showing a horizontally im-cted canine that has migrated across the midlined is lying inferior to the right mandibular canine.olor version of figure is available online)eatment Planning for Removal oranipulation of the Impacted Tooth

ce surgical intervention has been decided on,rough radiographic examination is needed totermine the position of the adjacent teeth andimportant anatomical structures. The proxim-of the tooth to a cortex (ie, buccal or lingual)l determine the approach the surgeon will take.e area must be examined for proximity to nerved vessel canals (such as the incisive canal/fora-n of the anterior maxilla and the inferior alve-r nerve [IAN] canal and mental foramen forndibular third molar and premolar extractionmanipulation). The ability of CBCT to projectse structures in three different planes decreaseschances of injuring them and the remaining

ntition. The axial plane allows for buccolingualessment of the tooth position (ie, lingual vsial placement, proximity to a cortex, and posi-n of the incisive canal/foramen in relation todline supernumeraries). The coronal plane can

ure 6. Coronal view showing lingual orientation ofimpacted left third molar. The position of the infe-r alveolar nerve canal can be evaluated. Note theen apices of the developing permanent dentition.

show mesiodistal tilt of the anterior teeth in addi-tion to providing sequential cross-sectional slicesthrough the IAN canal for detailed evaluation ofposterior tooth proximity. The sagittal plane canshow the mesiodistal orientation of the posteriorteeth as well as the faciolingual tip of the longaccess of the anterior teeth (Fig 1).

The advent of CBCT has been a monumentalevent for improving the diagnostic options andcapabilities of the orthodontist. Familiarity and fullutilization of its many options can provide thedentist with a valuable treatment planning tool.

References1. White SC, Pharoah MJ: Oral Radiology Principles and

Interpretation. Philadelphia, Mosby, 2004

2. Bankman IN: Handbook of Medical Imaging, Processingand Analysis. San Diego, Academic Press, 2000

3. McDonald RE, Avery DR, Dean JA: Dentistry for the childand adolescent. Philadelphia, Mosby, 2004

4. Fonseca LC, Kodama NK, Nunes FCF, et al: Radiographicassessment of Gardners syndrome. Dentomaxillofac Ra-diol 36:121-124, 2007

5. Kau CH, Richmond S, Palomo JM, et al: Three-dimen-sional cone beam computerized tomography in orth-odontics. J Orthod 32:282-293, 2005

6. Chaushu S, Chaushu G, Becker A: The role of digitalvolume tomography in the imaging of impacted teeth.World J Orthod 5:120-132, 2004

7. Mah J, Enciso R, Jorgensen M: Management of impactedcuspids using 3-D volumetric imaging. J Calif Dent Assoc31:835-41, 2003

8. Ericson S, Kurol PJ: Resorption of incisors after ectopiceruption of maxillary canines: a CT study. Angle Orthod70:415-423, 2000

62 D. Tamimi and K. ElSaid

Cone Beam Computed Tomography in the Assessment of Dental ImpactionsDetermining the Etiology for Dental ImpactionPathological FactorsDevelopmental Factors

Types of ImpactionEffect of Impacted Teeth on Surrounding StructuresTreatment Planning for Removal or Manipulation of the Impacted ToothReferences