-
Cone Beam Computed Tomography in theAssessment of Dental
ImpactionsDa
sisa
ic oly usnal lpacta, asf thstrf vien as ofprd 2
Rciatotwo-dimensional (2D) representation of three-dimensional
(3D) structures that often lie atvarious angles to the conventional
axial, coro-nal, and sagittal planes. Localization of
theseteeruataptrethuntio
matio
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
nosthis
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: [email protected] 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
-
ence of distortion, magnification, or superimpo-sitor
verseringsuanmeHUopthetaijecnegoawthewhthesegwil(Rmasegtatgestrin
DeIm
Imeruthtoorufuthunthepa
torlocthpeoptheter
impacts on treatment planning, as the appropri-ateplatre
Pa
OnnigpenatumsocmaanantioatoliaodboroufibmusynCBleswetio
De
ThthicidapbupatenlondusevThmiits(altheantioofcotoores
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
-
takcaustrgraCBmethoectthapeod
asnode
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
wh
Figu(B)imp
-
cotoocooratirelturocfulmaphno
Ty
Imthewhplapaaxoflarthdpaalidetyp(F
using plain film radiography, and may
warranttheagthrasstheingivtiostrprthe
Fighotio(Bshoanthefrothesio
Figstrmopaleftio
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)
-
EfSu
Theruthecodehaima catoocosligof
TrM
OnthodetheitywilThanmeolamaorthethedeassfactiomi
Figinglosne
Figstrpaan(C
Figanrioop
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