225

Characteristics of bony changes and tooth displacement in the mandibular cystic lesion involving the impacted third molar

Jin-Hyeok Lee1, Sung-Min Kim1, Hak-Jin Kim2, Kug-Jin Jeon3, Kwang-Ho Park1, Jong-Ki Huh1

1Department of Oral and Maxillofacial Surgery, Gangnam Severance Hospital, Yonsei University College of Dentistry, Seoul, 2Departments of Oral and Maxillofacial Surgery and 3Oral and Maxillofacial Radiology,

Yongin Severance Hospital, Yonsei University College of Dentistry, Seoul, Korea

Abstract (J Korean Assoc Oral Maxillofac Surg 2014;40:225-232)

Objectives: The purpose of this retrospective study is to find the differentiating characteristics of cystic and cystic-appearing lesions that involve the impacted mandibular third molar by analyzing panoramic radiographs and computed tomography images, and to aid the preoperative diagnosis. Materials and Methods: Eighty-one patients who had a mandibular cystic or cystic-appearing lesion that involved impacted mandibular third molar and underwent cyst enucleation were included in the study. The preoperative panoramic radiograph and computed tomography findings were analyzed in accordance to the histopathologic type. Results: Most of the cystic lesions containing the mandibular third molar were diagnosed as a dentigerous cyst (77.8%). The occurrence of mesio-distal displacement of the third molar was more frequent in the odontogenic keratocyst (71.4%) and in the ameloblastoma (85.7%) than in the dentigerous cyst (19.1%). Downward displacement was primarily observed in each group. Odontogenic keratocyst and ameloblastoma showed more aggressive growth pattern with higher rate of bony discontinuity and cortical bone expansion than in dentigerous cyst.Conclusion: When evaluating mandibular cystic lesions involving the impacted mandibular third molar, dentigerous cyst should first be suspected. However, when the third molar displacement and cortical bone absorption are observed, then odontogenic keratocyst or ameloblastoma should be con-sidered.

Key words: Third molar, Dentigerous cyst, Odontogenic cysts, Ameloblastoma, Mandible[paper submitted 2014. 7. 4 / revised 2014. 8. 23 / accepted 2014. 9. 7]

easilydetectedbypanoramicradiograph,whichiscommonly

usedindentalclinics2,buttheyusuallyshowsimilarradio-

graphicfeatures3.Thisoftenleadstounsuspectedpostopera-

tivehistologicfindingscontradicting thepredicted lesion

basedonradiographicfindings.Becausethegrowthpattern

andrecurrenceratedependonthehistologicalfeaturesofle-

sions,theinitialdifferentialdiagnosisiscrucialtoestablish-

ingtheappropriatetreatmentplanandpreventingpostopera-

tiverecurrence4.Inaddition,mandibularcysticlesionsoften

involveorareassociatedwith impactedmandibular third

molars(IMTMs),whichareoftenvisiblydisplacedinthese

cases.Thepresentstudyanalyzedthepanoramicradiograph

andcomputedtomography(CT)findings,andinvestigated

thecysticlesiongrowthpatternsandthirdmolardisplace-

mentdirectionsaccordingtothetypeoflesion,includingDC,

OKC,andAB,tocorrelatethehistopathologicandradiologic

characteristicsofcysticandcystic-appearinglesions.

I. Introduction

Thetypesofodontogeniccysticlesionsmostfrequently

encountered in theoralandmaxillofacial region include

dentigerouscyst(DC),radicularcyst,andodontogenickera-

tocyst(OKC)1.Ameloblastoma(AB),abenigntumor,may

alsoexhibitradiolucencyasacysticlesioninsomecases.

Differenttypesofcysticandcystic-appearinglesionscanbe

ORIGINAL ARTICLE

Jong-Ki HuhDepartment of Oral and Maxillofacial Surgery, Gangnam Severance Hospital, Yonsei University College of Dentistry, 211 Eonju-ro, Gangnam-gu, Seoul 135-720, KoreaTEL: +82-2-2019-4560 FAX: +82-2-3463-4052E-mail: omshuh@yuhs.ac

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

CC

Copyright Ⓒ 2014 The Korean Association of Oral and Maxillofacial Surgeons. All rights reserved.

http://dx.doi.org/10.5125/jkaoms.2014.40.5.225pISSN 2234-7550·eISSN 2234-5930

J Korean Assoc Oral Maxillofac Surg 2014;40:225-232

226

1. Displacement of the IMTM

UsingpanoramicradiographsandCTimages,theposition

anddisplacementoftheIMTMwasassessed.Thepositional

relationshipbetweenthecysticlesionandIMTMwasdeter-

minedasfollows:

1)Mesio-distal(MD)displacementanddirectionofIMTM

DisplacementoftheIMTMwascategorizedbydirection

asdiagnosedonpanoramicradiographs.Ifthecenterofthe

thirdmolarwaspositionedbelowthelinepassingthroughthe

roottipsoftheadjacentnormaleruptedsecondmolar,then

thedisplacementwascategorizedasdownward.Ifthecenter

ofthethirdmolarwaspositionedabovetheextendedlineof

theocclusalplane,thenthedisplacementwascategorizedas

upward.WhenthethirdmolarwasdisplacedbeyondtheMD

widthoftheadjacentsecondmolartowardsthedistalsideof

thesecondmolar,thenthedisplacementwascategorizedas

backward.Incasesofmissing,rootresorption,orectopicdis-

placementofthemesiallypositionedmolarteeth,theregion

II. Materials and Methods

Ofthe262patientswhounderwentcystenucleationbe-

tweenSeptember2005andApril2014afterbeingdiagnosed

withmandibularcysticorcystic-appearing lesionsat the

DepartmentofOralandMaxillofacialSurgeryinGangnam

SeveranceHospital,81patientswithobviouscysticlesions

involvingIMTMonpanoramicradiographswereselected

forthepresentstudy.Ofthese81subjects,53patientswere

male,28patientswerefemale,andtheirmeanagewas40.3

years.All81patientsunderwentpreoperativepanoramic

radiographs(Promax;Planmeca,Helsinki,Finland),and63

patientsunderwentCTimaging(SomatomSensation64scan-

ner;Siemens,Erlangen,Germany).Usingthepanoramicra-

diographsandCTfindingsofthemandibularcysticlesions,the

relationshipsbetweenthelesiongrowthpatternsandadjacent

teethwereinvestigatedbasedontheirrelationshipwithand

displacementofIMTM.Institutionalreviewboardapproval

wasgrantedattheinstitutionalreviewboardofYonseiUni-

versityGangnamSeveranceHospital(IRB#3-2014-0085).

Fig. 1. Tooth displacement patterns on panoramic radiographs. Any position that did not deviate from the described standard was consid-ered normal. A. a: Occlusal plane of the mesial teeth. b: The line parallel to (a), extending to the root tips of the second molar. c: The line per-pendicular to (a) and tangent to the height of the distal contour of the second molar. d: The line parallel to (c) and located behind the length of the mesio-buccal width of the second molar. B. Downward displacement. C. Backward displacement. D. Back-upward displacement.Jin-Hyeok Lee et al: Characteristics of bony changes and tooth displacement in the mandibular cystic lesion involving the impacted third molar. J Korean Assoc Oral Maxillofac Surg 2014

Fig. 2. Tooth displacement patterns on computed tomography imaging. A. No displacement. B. Lingual displacement. C. Buccal displacement.Jin-Hyeok Lee et al: Characteristics of bony changes and tooth displacement in the mandibular cystic lesion involving the impacted third molar. J Korean Assoc Oral Maxillofac Surg 2014

CA B

Radiographic characteristics of the mandibular cystic lesion involving the third molar

227

3. Growth pattern of mandibular cystic lesions

1)Anterior-posteriorgrowthpattern

Assumingthatacysticlesionoccurredinthenormalposi-

tionofthethirdmolarbehindthesecondmolar,thegrowth

patternofthecysticlesionwascategorizedasback-upward

whenthelesionexhibitedgrowthtowardsthecondylarhead

ofthemandible.Whenthelesionexhibitedgrowthtowards

themandibularborder,thegrowthpatternwascategorizedas

downward.Finally,whenthelesiongrowthwasdownward

towardsthesecondmolar,thegrowthpatternwascategorized

asdown-forward.(Fig.3)

2)BLgrowthpattern

Buccalandlingualgrowthwasdeterminedbyanalyzing

theCTaxialview.(Fig.4)

wasmeasuredassumingnormalposteriortootheruption.Any

positionthatdidnotdeviatefromthesestandardswasconsid-

erednormal.(Fig.1)

2)Bucco-lingual(BL)displacementoftheIMTM

IftheCTaxialviewshowedthat thecenterof thethird

molarwaspositionedonthearchcurvature,thenitwasdeter-

minedthatnodisplacementoccurred.Whenthecenterofthe

thirdmolardeviatedfromthearchcurvature,thedisplace-

mentofthethirdmolarwascategorizedasbuccalorlingual

displacement.(Fig.2)

2. Calculation of lesion size

IntheCTaxialview,thelargestMDwidthofthelesion

wasselectedandthelargestBLwidthperpendiculartothe

MDwidthwasmeasuredaccordingly.Theratiobetweenthe

BLwidthtotheMDwidthwasthencalculated5.

Fig. 3. Growth patterns of the lesion on displayed panoramic radiographs. A. Back-upward (arrow). B. Downward (arrow). C. Down-forward (arrow). D. Down-forward and back-upward (arrow). Jin-Hyeok Lee et al: Characteristics of bony changes and tooth displacement in the mandibular cystic lesion involving the impacted third molar. J Korean Assoc Oral Maxillofac Surg 2014

Fig. 4. Growth patterns of the lesion shown on computed tomography imaging. A. Buccal (asterisk). B. Bucco-lingual. C. Lingual (asterisk).Jin-Hyeok Lee et al: Characteristics of bony changes and tooth displacement in the mandibular cystic lesion involving the impacted third molar. J Korean Assoc Oral Maxillofac Surg 2014

J Korean Assoc Oral Maxillofac Surg 2014;40:225-232

228

ityaroundthelesion,andtheMann-Whitneytestwasusedto

analyzetheBL/MDratiooflesions.

III. Results

Thepresent study investigated81casesofcysticand

cystic-appearinglesionsinvolvingtheIMTMbyperforming

acomparativeanalysisofthepanoramicradiographsandCT

scansoftherespectivelesionsandobtainedthefollowingre-

sults.

Ofthe81cysticlesions,DCwasthemostcommontypeat

77.8%(63/81cases),followedbyOKCandABat8.6%(7/81

cases)each.Theothers included3paradentalcystsand1

glandularodontogeniccyst.Themeanpatientageofthethree

majorgroupswas42.5,33.9,and22.9yearsintheDC,OKC,

andABgroup,respectively.(Table1)

ThepanoramicradiographsrevealedaMDdisplacement

incidenceof the thirdmolarsof28.4%(23/81cases)and

anincidencerateaccordingtolesiontypeof19.1%(12/63

cases),71.4%(5/7cases),and85.7%(6/7cases)fortheDC,

OKC,andABgroup,respectively.TheincidenceofMDdis-

placementintheDCgroupwassignificantlylowerthanthat

ofthenon-DCgroup,andtheoddsratiooftheIMTMwas

4. Occurrence of cortical bone expansion and loss

of bony continuity

Theoccurrenceofcorticalboneexpansionandlossofbony

continuityonthecysticlesionsweredeterminedbyanalyzing

theCTscans.

5. Root resorption

Rootresorptionofadjacenttoothwasassessedonlywhen

thelesioninvolvedtherootoftheadjacenttooth.

6. Statistical analysis

DatawereanalyzedusingthePASWStatistics18.0(IBM

Co.,Armonk,NY,USA).Lesionswereclassifiedintoeither

theDCgroupornon-DCgroup.Thenon-DCgroupincluded

OKCandAB.Becauseparadentalcystsandglandularodon-

togeniccystswereveryrare,wedidnotconsidertheminthe

statisticalanalysis.Fisher’sexacttestwasusedtoanalyze

MDandBLdisplacementoftheIMTM,corticalboneexpan-

sionofthelesionandrootresorptionoftheadjacenttooth.

Chi-squaretestwasusedtoanalyzethelossofbonecontinu-

Table 2. Displacement type of impacted mandibular third molar

Displacementtype

Displacement Direction DCNon-DC

Others Total P-valueOKC AB

Mesio-distal

Bucco-lingual

NoYes

TotalNoYes

Total

DownwardBackwardBack-upward

BuccalLingual

51(80.9)9(14.3)1(1.6)2(3.2)6345(91.8)0(0)4(8.2)49

2(28.6)4(57.1)0(0)1(14.3)74(80)0(0)1(20)5

1(14.3)3(42.9)2(28.6)1(14.3)76(85.7)1(14.3)0(0)7

4(100)0(0)0(0)0(0)42(100)0(0)0(0)2

58(71.6)16(19.8)3(3.7)4(4.9)81(100)57(90.5)1(1.6)5(7.9)63(100)

0.0011

0.5582

(DC:dentigerouscyst,OKC:odontogenickeratocyst,AB:ameloblastoma,Others:paradentalcystandglandularodontogeniccyst)1Comparisonofmesio-distaldisplacementbetweentheDCandnon-DCgroups.2Comparisonofbucco-lingualdisplacementbetweentheDCandnon-DCgroups.Dataarepresentedasnumberornumber(%).Jin-Hyeok Lee et al: Characteristics of bony changes and tooth displacement in the mandibular cystic lesion involving the impacted third molar. J Korean Assoc Oral Maxillofac Surg 2014

Table 1. Age and sex distributions according to pathologic diagnosis

DiagnosisNumberofpatients

Meanage(yr) Total,n(%)Male Female

DentigerouscystOdontogenickeratocystAmeloblastomaParadentalcystGlandularodontogeniccystTotal

41362153

22411028

42.533.922.951.73840.3

63(77.8)7(8.6)7(8.6)3(3.7)1(1.2)81(100)

Jin-Hyeok Lee et al: Characteristics of bony changes and tooth displacement in the mandibular cystic lesion involving the impacted third molar. J Korean Assoc Oral Maxillofac Surg 2014

Radiographic characteristics of the mandibular cystic lesion involving the third molar

229

buccalandlingualgrowth,whereas,alloftheABandOKC

groups(5/5and7/7cases,respectively)exhibitedsimultane-

ousgrowthinthebuccalandlingualdirections.(Table4)

Corticalboneexpansionwasobservedin67.3%(33/49

cases)ofcases in theDCgroup.Both theOKCandAB

groupsexhibitedcorticalboneexpansionin100%ofcases

(5/5and7/7cases,respectively).Alossofbonecontinuity

wasobservedin36.7%(18/49)ofcasesintheDCgroup,

60%(3/5)ofcasesintheOKCgroup,and71.4%(5/7)of

casesintheABgroup.(Table5)

Rootresorptionintheadjacentsecondmolarwasfoundin

58.3%(21/36)ofcasesintheDCgroup,66.7%(2/3)ofcases

intheOKCgroup,and67.7%(4/6)ofcasesintheABgroup.

(Table6)

IV. Discussion

Themostcommonclinical symptomofamandibular

cysticlesionispain,sometimesaccompaniedbyswelling.

Otherclinicalsymptomsincludeparesthesia,toothdisplace-

ment,andtoothmobility.However,thepresenceorabsence

ofclinicalsymptomsdoesnotalwaysaid thedifferential

15.6(95%confidenceinterval,3.8to64.7).Thedirectionof

MDdisplacementwastypicallydownward,accountingfor

69.6%(16/23cases)ofthelesionsexhibitingdisplacement.

Otherlesiontypesshowednoevidenceoftoothdisplacement.

WhenBLdisplacementofthethirdmolarwasobservedon

theCTaxialview, thetoothwasmostcommonlyaligned

onthearchcurvaturein90.5%(57/63)ofcases;incontrast,

only7.9%(5/63)ofcasesexhibitedlingualdisplacement,and

1.6%(1/63)ofcasesexhibitedbuccaldisplacement.(Table2)

TheratiosofBLtoMDwidth(BL/MDratio)oftheOKC

andABgroupwere0.78and0.81,respectively,whichwere

significantlygreaterthantheBL/MDratiooftheDCgroup

(0.65).(Table3)

WhentheMDgrowthpatternofthelesionswasinvestigat-

ed,theDCgroupmostcommonlyexhibiteddown-forward

growthalonein41.3%(26/63)ofcases.IntheABandOKC

group,themajorityoflesionsexhibitedbothdown-forward

andback-upwardgrowthsimultaneously, in42.9%(3/7)

ofcasesand71.4%(5/7)ofcases,respectively,higherthan

15.9%(10/63)ofcasesintheDCgroup.

Inthelesionsexhibitingabuccalorlingualgrowthpattern,

69.4%(34/49cases)oftheDCgroupexhibitedsimultaneous

Table 3. Ratio between bucco-lingual (BL) width and mesio-distal (MD) width of lesions

Widthandratio DCNon-DC

Others P-valueOKC AB

BLwidth(mm)MDwidth(mm)BL/MDratio

12.5720.660.65

14.9419.260.78

21.7427.930.81

12.7416.650.79

--

0.0041

(DC:dentigerouscyst,OKC:odontogenickeratocyst,AB:ameloblastoma,Others:paradentalcystsandglandularodontogeniccyst)1ComparisonofratiobetweentheDCandnon-DCgroups.Jin-Hyeok Lee et al: Characteristics of bony changes and tooth displacement in the mandibular cystic lesion involving the impacted third molar. J Korean Assoc Oral Maxillofac Surg 2014

Table 4. Growth pattern of mandibular cystic lesions

Image Growth DCNon-DC

Others TotalOKC AB

Panoramicview

CTview

InsidethereferencelineDownwardDown-forwardUp-backwardDown-forwardandup-backwardTotalCentralBuccalLingualBuccalandlingualTotal

7(11.1)7(11.1)26(41.3)13(20.6)10(15.9)633(6.1)1(2.0)11(22.4)34(69.4)49

0(0)1(14.3)1(14.3)2(28.6)3(42.9)70(0)0(0)0(0)5(100)5

0(0)0(0)1(14.3)1(14.3)5(71.4)70(0)0(0)0(0)7(100)7

0(0)2(50)2(50)0(0)0(0)40(0)0(0)0(0)2(100)2

7(8.6)10(12.3)30(37.0)16(19.8)18(22.2)81(100)3(4.8)1(1.6)11(17.5)48(76.2)63(100)

(DC:dentigerouscyst,OKC:odontogenickeratocyst,AB:ameloblastoma,Others:paradentalcystsandglandularodontogeniccyst,CT:computedtomography)Dataarepresentedasnumberornumber(%).Jin-Hyeok Lee et al: Characteristics of bony changes and tooth displacement in the mandibular cystic lesion involving the impacted third molar. J Korean Assoc Oral Maxillofac Surg 2014

J Korean Assoc Oral Maxillofac Surg 2014;40:225-232

230

lesionscaninfluenceprognosis,includingthepostoperative

recurrencerate.Assuch,amoreaccurateinitialdifferential

diagnosiswouldaidsurgeons4.Forinstance,patientsshould

bewarnedoftheaggressivegrowthpotentialandlikelihood

ofrecurrencepreoperatively;furthertreatmentsuchascuret-

tage,grindingorevenradicalresectionmightbeconsidered

whenOKCorABissuspectedbasedontheradiographicex-

aminations.

DCs,OKC,andABlesionsexhibitmorphologicdiffer-

encesduetotheirvaryinginternalcompositionsandborder

patterns.WhenOKCandDCarecompared,thehistopatho-

logicpatterns,particularlythepresenceofkeratin,determine

thelesionmorphology5.WhentheCTfindingsofABand

DClesionsarecompared,theformerexhibitsamoreaggres-

sivegrowthpatternthanthelatter6.Inaddition,theanatomic

position,growthperiod,andlesionsizecanleadtodiffer-

encesinlesionmorphology,andthedifferentgrowthpatterns

of thelesionscaninfluencedisplacementof theimpacted

tooth7.Consequently,thepresentstudysoughttoidentifythe

characteristicfindingsofthesedifferentlesionsbyinvestigat-

ingthegrowthpatternsofmandibularcysticlesionsandthe

displacementoftheIMTM.

diagnosis.Furthermore,earlylesionsareoftenasymptom-

atic,andinmostcases,lesionsaredetectedonroutinedental

radiographs,suchaspanoramicradiographs,priortoapatient

beingawareofthem3.Insuchsituations,thedentistshould

informpatientsaboutthediscoveredlesions.

Radiologicdifferentialdiagnosisofcysticlesionsisper-

formedbyconsideringthemorphologicfindingsandtherela-

tionshiptoadjacentstructures.Evenlesionsexhibitingiden-

ticalhistopathologicfindingscanshowvaryingradiologic

featuresdependingontheirposition,size,andgrowthstage.

Conversely,distincthistopathologiclesionsmayexhibitsimi-

larradiologicfeatures,thusposingdifficultiesindifferential

diagnosis4.

Althoughcysticlesionscanbeconfirmedbypreoperative

biopsyinsomecases,itisimpracticaltoperformabiopsyfor

everylesion.Therefore,preoperativeclinicalandradiologic

differentialdiagnosesareperformedinmanycases.Conse-

quently,thepostoperativehistopathologicfindingsafterbi-

opsymaydifferfromthepreoperativelypredictedresults3.

Themajorityofmandibularcystic lesionsarebenign,

butcertain lesionscanbeshowaggressiveordestructive

growth3.Thedifferinghistopathologiccharacteristicsofthe

Table 6. Root resorption of the adjacent second molar on computed tomography1

Rootresorption DCNon-DC

Others Total P-valueOKC AB

YesNoTotal

21(58.3)15(41.7)36

2(66.7)1(33.3)3

4(66.7)2(33.3)6

1(50)2

1(50)3

2

28(59.6)19(40.4)47(100)

0.7214

(DC:dentigerouscyst,OKC:odontogenickeratocyst,AB:ameloblastoma,Others:paradentalcystandglandularodontogeniccyst)1Onlyassessedwhentherootoftheadjacentsecondmolarwasinvolvedinthelesion.2Paradentalcyst,3glandularodontogeniccyst.4ComparisonofrootresorptionbetweentheDCandnon-DCgroups.Dataarepresentedasnumberornumber(%).Jin-Hyeok Lee et al: Characteristics of bony changes and tooth displacement in the mandibular cystic lesion involving the impacted third molar. J Korean Assoc Oral Maxillofac Surg 2014

Table 5. Occurrence of cortical bone expansion and loss of bony continuity on computed tomography image

Direction DCNon-DC

Others Total P-valueOKC AB

NoexpansionCorticalboneexpansion

Lossofbonycontinuity

Total

BuccalLingualBuccalandlingualYesNo

16(32.7)1(2.0)11(22.4)21(42.9)18(36.7)31(63.3)49

0(0)0(0)0(0)5(100)3(60)2(40)5

0(0)0(0)0(0)7(100)5(71.4)2(28.6)7

0(0)0(0)0(0)2(100)2(100)0(0)2

16(25.4)1(1.6)11(17.5)35(55.6)28(44.4)35(55.6)63(100)

0.0261

0.1022

(DC:dentigerouscyst,OKC:odontogenickeratocyst,AB:ameloblastoma,Others:paradentalcystsandglandularodontogeniccyst)1ComparisonofcorticalboneexpansionbetweentheDCandnon-DCgroups.2ComparisonoflossofbonycontinuitybetweentheDCandnon-DCgroups.Dataarepresentedasnumberornumber(%).Jin-Hyeok Lee et al: Characteristics of bony changes and tooth displacement in the mandibular cystic lesion involving the impacted third molar. J Korean Assoc Oral Maxillofac Surg 2014

Radiographic characteristics of the mandibular cystic lesion involving the third molar

231

shape6.Becauseof theelevated internalpressure induced

bykeratindepositionat theepitheliumofthecystandthe

strongosteoclastactivityofprostaglandinsgeneratedbythe

epithelialcells,OKCexhibitsafastergrowthpattern.ABis

alsoknowntoberelativelyinvasiveandaggressive14.Inthis

study,OKCandABshowedahighBL/MDratio,presum-

ablybecauseoftheirfastergrowthrateandmoredestructive

tendencycomparedtoDC.Therefore,thesetwolesionspre-

cipitatebuccalandlingualcorticalboneexpansion,further

acceleratingBLgrowthofthelesion.Consequently,thecys-

ticlesionscausedbythesetwoetiologieshaveamorecircu-

larshapeontheCTaxialviewcomparedtotheovalshaped

lesionsoftheDCgroup.Inthisstudy,aswell,theBL/MD

ratiowassignificantlyhigherintheOKCandABgroupthan

intheDCgroup.

Thegrowthdirectionofthelesionisalsopresumablyas-

sociatedwiththegrowthpatternof thelesion.WhenMD

growthofthelesionwasobserved,theDCgroup,whichhas

relativelyslowgrowing lesions,predominantlyexhibited

unilateralgrowth.WhenBLgrowthof thelesionwasob-

served,arelativelyhighproportionofDCs(22.4%)exhibited

unilateralgrowthtowardsthelingualside.Incontrast,100%

oftheABandOKCcasesexhibitedsimultaneousbuccaland

lingualgrowth.

Aslesionsgrow,largelesionsmaycausecorticalboneex-

pansion,lossofbonycontinuityandrootresorptionofthead-

jacenttooth14.Thefactthatcorticalboneexpansionandloss

ofbonycontinuitywasgreaterintheOKCandABgroups

thantheDCgroupdemonstratesthedifferentgrowthrates

andaggressivenessamongthedifferentlesions17.

Notably,whenrootresorptionrateswereinvestigatedin

caseswherealesioninvolvedtherootoftheadjacentsec-

ondmolar,theOKCandABgroupeachexhibiteda66.7%

rootresorptionrate.DCsalsoexhibitedarelativelyhighroot

resorptionrateof58.3%,thusdemonstratingthatrootresorp-

tionaloneisnotusefulfordifferentialdiagnosis.

Furtherresearchbasedonagreaternumbercasesincluding

othertypesofcysticlesionsisneededforfuturestudies.

V. Conclusion

MDdisplacementofIMTMandcorticalboneexpansion

weresignificantlyhigherintheOKCandABgroupsthanin

theDCgroup.However,BLdisplacement,lossofcontinuity

androotresorptiondonotseemtobehelpfulforthedifferen-

tialdiagnosisofcysticlesions.Whenacysticlesioninvolv-

inganIMTMappearsonpanoramicradiographs,DCmay

Themostcommontypeofodontogeniccyst,DC,ispres-

entin46%8to53%9ofimpactedthirdmolars10.OKCisalso

closelyassociatedwithanimpactedtoothandisthesecond

mostcommonodontogeniccyst11.Inastudyinvestigatingthe

prevalenceoftumorsandcysticlesionsassociatedwith9,994

impactedthirdmolars,cysticlesionsweremorecommonly

observed(2.31%;n=231) than tumorous lesions.Among

tumors,ABwas themost commonlyobserved (0.41%,

n=41)12andwasidentifiedasthemostcommonodontogenic

tumor4,12-14.Amongthe81cysticlesionsinvestigatedinthis

study,DCswere themostcommon, representing77.8%

ofcases,followedbyOKCandABin8.6%ofcaseseach.

WhenacysticlesioninvolvinganIMTMappearsonpan-

oramicradiographs,thereisahighprobabilitythatthecystic

lesionisaDC.

DCsareknowntooccurmorefrequentlyinpatientsaged

20yearsorolder8,9; themeanageoftheDCgroupinthis

studywas42.5years.OKCgenerallyoccursinpatientsbe-

tweenages20to50years15;themeanageoftheOKCgroup

inthisstudywas33.3years.ABmosttypicallyoccursinpa-

tientsbetweentheageof20to40years10,13;themeanageof

theABgroupinthisstudywas22.9years.

Thirdmolarsinvolvedincysticlesionsexhibitmoresevere

impactionpatternsthanthoseuninvolvedincysticlesions16.

Tsukamotoetal.7reportedthataggressiveproliferationof

a lesionisunlikelytocausetoothdisplacement,ascribing

thisobservationtotherapidgrowthoftheselesions,which

providesinsufficienttimeforthethirdmolartobecomedis-

placed.However,theincidenceofMDdisplacementwasthe

lowestintheDCgroupinthisstudy.Thisresultmayreflect

thefocusofthepresentstudy;ratherthanexaminingthecor-

relationbetweenlesionsizeanddisplacementseverity,this

studyfocusedontheabsenceorpresenceoftoothdisplace-

ment.Duetofocusingonlyonthepresenceoftoothdisplace-

ment, therewasahighprobabilitythatacysticlesionwas

OKCorABwhenMDdisplacementwasobserved.

WhenBLdisplacementofthethirdmolarwasobserved

ontheCTaxialview,therewasahigherincidenceoflingual

displacementcomparedtobuccaldisplacement,presumably

becausethecorticalboneisrelativelythinnerlingually,which

favors thirdmolardisplacement towards the lingualside.

However,thedifferenceintheincidenceofBLdisplacement

betweentheDCandnon-DCgroupwasnotstatisticallysig-

nificant.

Comparedtomaxillarylesions,mandibularlesionshave

limitedspaceforgrowthowingtobuccalandlingualfirm

corticalbone,andthus,growmesio-distallyinalongoval

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232

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firstbesuspected,becauseDCisthemostcommontypeof

cysticlesion.However,whenMDdisplacementofthethird

molarandcorticalboneresorptionareobserved,thenOKC

orABshouldbeconsidered.Thismayassistwithpreopera-

tivediagnosisandguidethetreatmentofcysticandcystic-

appearinglesionsinvolvinganIMTM.

Conflict of interest

Nopotentialconflictofinterestrelevanttothisarticlewas

reported.

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