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2 0 1 4 년

2 월 석 사 학 위 논 문 부 정 교 합 환 제 에서

CBCT

를 이 용 한 절 치、 견 치、 소 구 치 의 치 관 과 치 근 길 이 계 측 김 선 영

2014년 2월 석사학위 논문

부정교합 환자에서 CBCT를 이용한 절치,견치,소구치의

치관과 치근 길이 계측

조 선 대 학 교 대 학 원

치 의 학 과

김 선 영

[UCI]I804:24011-200000264315

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치관과 치근 길이 계측

Cr ownandr ootl e ngt hofi nc i s or s ,c a ni ne sand pr e mol ar sme as ur e dbyc one -be am c omput e d

t omogr a phyi npat i e nt swi t hmal oc c l us i on

2014년 2월 25일

치 의 학 과

김 선 영

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치관과 치근 길이 계측

지도교수 임 성 훈

이 논문을 치의학 석사학위신청 논문으로 제출함

2013년 10월

치 의 학 과

김 선 영

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김선영의 석사학위 논문을 인준함

위원장 조선대학교 교 수 김 흥 중 ( 인) 위 원 조선대학교 교 수 임 성 훈 ( 인) 위 원 조선대학교 조교수 강 성 남 ( 인)

2013년 11월

조 선 대 학 교 대 학 원

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목 차

표목차

--- ii

도목차

--- iii

ABSTRACT

--- iv

I . I nt r oduc t i on

--- 1

I I .Mat e r i al sandMe t hods

--- 3

Ⅲ.Re s ul t s

--- 6

Ⅳ.Di s c us s i on

--- 7

Ⅴ.Conc l us i ons

--- 10

Re f e r e nc e s

--- 11

Tabl e s

--- 15

Fi gur e s

--- 19

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표 목 차

Table1. CharacteristicsofthesubjectsfortheCBCT-basedincisor,canine, andpremolarlengthmeasurements---15 Table2. ComparisonoftheCBCT-basedanddirecttoothlength

measurementsoftheextractedpremolars---16 Table3. ComparisonoftheCBCT-basedtoothlengthmeasurementsofthe

maleandfemalesubjects---17 Table4. CBCT-basedrootlengthmeasurementsoftheincisors,canines,

andpremolarsbygender---18

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도 목 차

Fig1. Schematicofthelandmarksusedformeasuringthetotaltooth, crown,androotlengthsoftheextractedpremolars---19 Fig2. Alignmentprocedureofmultiplanarreconstructionwindowsfor

theCBCT-basedlengthmeasurements---19 Fig3. Bland-AltermanplotsoftheCBCT-basedanddirectlength

measurementsoftheextractedpremolars---22

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ABSTRACT

Cr ownandr ootl e ngt hofi nc i s or s ,c a ni ne sandpr e mol ar s me as ur e dbyc one -be am c omput e dt omogr aphyi npa t i e nt s

wi t hmal oc c l us i ons

Seon-YoungKim

Advisor:Prof.Sung-HoonLim,DDS,MSD,PhD DepartmentofDentistry

GraduateSchoolofChosunUniversity

Objective:이 논문의 목적은 cone-beam computedtomography (CBCT)를 이용 하여 계측한 치관과 치근 길이를 교정치료를 위하여 발치한 소구치의 길이와 비 교함으로써 CBCT의 정확성을 평가하고 CBCT를 이용하여 부정교합 환자에서의 전치,견치,소구치의 길이의 데이터를 얻고자 하였다.

Methods:CBCT 영상은 CB MercuRay (Hitachimedical,Osaka,Japan)를 이용 하여 얻어졌다.금속 수복물이 없는 94개의 발치된 소구치의 실제 길이와 CBCT 에서 계측한 길이를 비교하기 위하여 pairedt-test가 시행되었다.부정교합 환자 에서의 전치,견치,소구치 길이의 데이터를 얻기 위하여 62명의 환자의 CBCT 영상에서 길이 계측이 시행되었으며 Pearson상관계수를 각 치아의 치관과 치근 길이 사이의 관계를 살펴보기 위해 구하였다.

Results:실제 길이와 CBCT 계측 길이는 통계적으로 유의한 차이가 나지 않았 다.95% 신뢰구간의 2SD 범위는 치관 길이에서 -0.90~0.90mm,치근 길이에 서 -1.23~1.18mm 였다.치관과 치근 길이 사이에는 하악 견치와 소구치에서 만 약한 상관관계가 관찰되었다.

Conclusions:CBCT 계측 길이는 치근 길이에서 가장 넓은 범위의 신뢰구간의

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2SD범위를 보였다.이 연구에서 계측된 CBCT 계측 길이는 금속 수복물을 갖지 않은 부정교합 환자들의 치근 길이와 치근 흡수를 평가하는데 참고치로 사용될 수 있다.

Keywords:Computedtomography;Anatomy;Rootresorption

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Ⅰ.I nt r oduct i on

Inflammatory root resorption is an unavoidable pathologic consequence of orthodontic tooth movement.¹^–3The incidence ofrootresorption is reportedly 1– 86% in nonorthodontically treated patients and 19–93% in orthodontically treated patients.⁴Evaluationoftheseverityofrootresorptionrequirestheestablishmentof referencedataon thenormalrootlength.Early studies⁵^–1¹used extracted teeth to derive these measurements,butthe difficulty in collecting undamaged extracted teeth always limited the sample size.In many other studies,¹²^–1⁹ periapicalor panoramic radiographs were used to measure root length. However, two-dimensionalimagesdonotallow accuratemeasurement:periapicalradiographs are distorted depending on the angle between the film and the tooth¹²^–1⁴ and panoramic radiographs show verticalmagnification.¹⁵^–19Panoramic radiographs are alsosensitivetopatientpositioning;evenunderoptimalconditions,theyarefraught withuncertainty,particularlyintheanteriorjaw regions.²⁰

Cone-beam computed tomography (CBCT) is an alternative technology for evaluating rootlength orresorption before,during,andafterorthodontictreatment. Sherrard etal²¹ compared CBCT images and periapicalradiographs ofextracted porcine teeth to determine the accuracy and reliability of CBCT-based measurementsand reported thattheCBCT-based measurementsofthetotaltooth androotlengthsdid notdiffersignificantly from theactuallengths.Further,Lund etal²⁰measuredrootlengthandthemarginalbonelevelin13livingpatientsand1 dry skull and concluded that CBCT yielded a high level of measurement reproducibility.CBCT-basedmeasurementsofpatientscanbemoredifficultdueto patientmovementduringimaging.

Thepurposes ofthisstudy wereto determine theaccuracy ofcrown and root length measurements of premolars by CBCT by comparing them with direct measurements of subsequently extracted premolars and to provide reference CBCT-basedmeasurementdatafortheincisors,canines,andpremolarsofpatients with malocclusions.Thenullhypothesiswasthatthereisnodifferencein crown,

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root, and tooth length measurements between CBCT-based and direct measurements.

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Ⅱ.Mat er i al sandMet hods

This work was approved by theethics committee ofChosun University Dental Hospital,Gwangju,Korea (CDMDIRB 1218-85).All the subjects gave written consentafterthepurposesofthestudywereexplainedtothem.

AssessmentoftheaccuracyofCBCT-basedlengthmeasurementsofpremolars

Fifty-twoKorean patientswhoneeded premolarextraction wereselected from a population of patients who visited the Department of Orthodontics, Chosun University Dental Hospital for orthodontic assessment. The premolars were extracted after the patients had undergone CBCT imaging. Among the 152 premolars extracted, 58 were excluded because of the presence of metal restorations,incomplete growth of the root apex or presence of obvious root resorption,presenceofa periapicallesion,presenceofsevereocclusalattrition,or poorCBCT-imagequality.Finally,94premolarsextractedfrom 21male(meanage, 22.3 ± 3.0 years;age range,16–30 years)and 21 female (mean age,20.3 ± 4.1 years;agerange,16–33years)patientswereusedasspecimens.

Theteethweremeasuredbyusingadigitalcaliperwitharesolutionof0.01mm (Mitutoyo Corp.,Kawasaki,Japan).The following definitions were used forboth thedirectandtheCBCT-basedmeasurements(Figure1):

1 Crown length: distance between the buccal cusp tip and the buccal cementoenameljunction(CEJ)

2.Rootlength:distancebetweenthebuccalCEJandtherootapex 3.Toothlength:distancebetweenthebuccalcusptipandtherootapex

In teeth with twoapices,thebuccalrootapex wasused forthemeasurements. Images were obtained using a CBCT scanner (CB MercuRay,HitachiMedical, Osaka,Japan)with the following parameters:149.5 × 149.5 mm field ofview,15 mA,120kV,9.6-sscantime,0.292-mm isometricvoxelsize,and12-bitgrayscale.

Measurements were derived from the CBCT images using OnDemand3D 1.0

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software(Cybermed,Inc.,Seoul,Korea).Thewindowing width andlevelwereset according totheCB MercuRay tooth preset(width,1726HU;level,870HU;range, 7–1733HU)tomaintain aconstantviewing condition.Toenhanceedgedetection, acolorgradientmap(rainbow colorpalettepreset)wasappliedby using thecolor palettedialog toolunderthe“finetuning”tab oftheOnDemand3D program.This toolgenerates color-mapped images according to HU values.The rainbow color palette presetconverts pixels over 1733 HU into red,pixels under 7 HU into purple,andpixelsfrom 7to1733HU intorainbow colorsbetween redandpurple. Thealignmentprocedureofthemultiplanarreconstruction windowsisdepicted in Figure2.

CBCT-basedmeasurementsofincisors,canines,andpremolars

Thetotal,crown,and rootlengthsoftheincisors,canines,and premolarswere measured by using pretreatmentCBCT imagesof31maleand 31femalepatients with malocclusions. The sample characteristics are shown in Table 1. A preliminary study showed no significantdifference between therightand theleft teeth;therefore,maxillaryrightteethandmandibularleftteethweremeasured.

Themeasurementprocedureswerethesameasthoseused fortheCBCT-based measurementsin thefirstpartofthestudy (Figure2).Fortheanteriorteeth,the incisaledgeorcusptipwasusedasthereferencepointinsteadofthebuccalcusp tip.In addition,the root-to-crown (R/C)ratios ofthe teeth were calculated by dividingtherootlengthbythecrownlength.

Statisticalanalysis

Allofthemeasurementsoftheextractedpremolarswererepeatedafter2weeks by one investigator (S.Y.K),and Dahlberg's formula was used to quantify the method error. The Kolmogorov–Smirnov normality test revealed that normal distributions could be assumed for the direct and CBCT-based length measurements of the extracted premolars and the CBCT-based length measurements of the incisors, canines, and premolars. However, when the

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CBCT-based length measurements ofthe incisors,canines,and premolars were divided according to gender,the assumption ofnormaldistribution was rejected.

The paired t-testand Bland–Altman plots were used to compare the directand CBCT-basedlengthmeasurementsoftheextractedpremolars.Pearson'scorrelation coefficients were used to analyze the relationship between the crown length and the root length of each tooth type.The Mann–Whitney U-test was used to evaluate gender differences.The Kruskal–Wallis test and multiple comparisons were used to testthe difference in rootlength among the tooth types in each gender.

The results were considered significantatP < 0.05.Bland–Altman plots were generated by using MedCalc 12.4.0 software (MedCalc Software, Mariakerke, Belgium),and the otheranalyses were performed in SPSS 12.0 software (SPSS Inc.,Chicago,IL,USA).

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Ⅲ.Resul t s

The method error values ofthe directlength measurements ofthe extracted premolarsweresmallerthan thoseoftheCBCT-based length measurements.The method errorvaluesofthedirectmeasurementsofcrown,root,and tooth lengths were 0.18, 0.33, and 0.10 mm, respectively, and those of the CBCT-based measurementswere0.29,0.82,and0.28mm,respectively.

With respectto totallength,the CBCT-based measurements were 0.18 ± 0.44 mm shorter than the directmeasurements (P < 0.001).However,no significant differences in crown and rootlengths were noted between the CBCT-based and direct measurements (Table 2).Bland–Altman plots showed only small mean differences,implying strong agreement(Figure 3).The 95% limits ofagreement were−0.90to0.90mm forcrown length,− 1.23to1.18mm forrootlength,and

− 1.04to0.68mm fortotallength.

The correlation coefficients between crown and rootlengths were 0.335 (P = 0.008) for the mandibular canine,0.264 (P = 0.038) for the mandibular first premolar,and 0.269 (P = 0.036) for the mandibular second premolar.No other significantcorrelationswereevident.

A significantgender difference in the CBCT-based length measurements was noted:the mean crown,root,and totallengths were significantly greaterin men (Table 3).However,the R/C ratio showed no significantgenderdifference (P = 0.807).

The Kruskal–Wallis testrevealed significantdifferences in rootlength among the tooth types in both the male and female subjects. Multiple comparisons revealedthatthemaxillaryandmandibularcanineshadthelongestrootswhilethe mandibularcentralincisorhadtheshortestrootinthemalesubjects;inthefemale subjects,themaxillary and mandibularcanines and mandibularfirstpremolarhad thelongestrootswhilethemandibularcentralincisorhadtheshortestroot(Table 4).

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Ⅳ.Di scussi on

When measuring tooth length from periapical radiographs, the likelihood of distortionrelativetotheprojectionangleoftheX-rayunitshouldbeconsidered.¹^2,¹⁴ Brezniak et al¹⁴ stated that the median CEJ is the best reference point for measuring rootlengthviaperiapicalradiographs.Toovercomethedrawbackofthe projection angle in periapical radiographs,R/C ratios were measured in some studies.¹^8,¹⁹Inthepresentstudy,thebuccalCEJwasusedasthereferenceforthe crown androotlengthmeasurementsbecauseitcan belocatedeasily on extracted teeth;moreover,in contrastto periapicalradiographs,no distortion ofthe buccal CEJoccursinCBCT images.

Stratemann et al²² reported that the differences between direct caliper measurements (the “gold standard”)and measurements generated from NewTom and CB MercuRay scanning were as low as 0.07 ± 0.41 and 0.00 ± 0.22 mm, respectively.Pinsky etal²³studiedtheaccuracyofCBCT-basedmeasurementsand reported that the mean width and height accuracies for the measurement of intraosseous defects were−0.07 mm and −0.27 mm, respectively. Moreover, Baumgaertel et al.²⁴ investigated the reliability and accuracy of dental measurements on CBCT images of30 skulls and reported thatthe compounded measurementsofCBCT likerequired spaceand availablespacetended to slightly underestimatetheanatomic values.In thepresentstudy,thedifferencesin crown and root length measurements were not significant. However, the limits of agreementintheBland–Altmanplotfortherootlengthmeasurementswerewider apartthan thoseforthecrown length measurements,ranging from −1.23to 1.18 mm.Thisfinding meansthatrootlength measured by CBCT willdifferfrom the truerootlengthby−1.23to1.18mm in95% ofcases.

Sherrard etal²¹ reported thatthe method error values oftooth measurements increase with the voxelsize:in theirstudy,the method errorvalues were 0.266 mm fortotallength and 0.440 mm forrootlength when the voxelsize was 0.3 mm.Ponderetal²⁵alsoreportedthatthemeasurementofrootresorptionwasmore

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accurate when CBCT was performed with a smaller voxelsize.In the present study,themethoderrorvaluesoftheCBCT-basedmeasurementswerelargerthan those ofthe directmeasurements ofthe extracted premolars.The CBCT-based measurementsofthecrownandtotallengthsexhibitedmethoderrorvaluessimilar toorslightlylargerthanthevoxelsize(0.292mm)used.

However,the method error value for rootlength was nearly three times the voxelsize.Thesefindingshighlightthedifficulty inlocating arootapex onCBCT images.

Ozakietal¹⁰foundthatthemean valuesofalltooth dimensionsweregreaterin male subjects than in female subjects.In the presentstudy,the measurementof every tooth type investigated was significantly longer in the male subjects. Verhoeven et al⁶ reported that the centralincisor was longer than the lateral incisorinthemaxillaandthelateralincisorwaslongerthanthecentralincisorin themandible.Thetotallengthsexhibited asimilartendency in thepresentstudy, but the mandibular centralincisor had the shortest root and maxillary central incisorhadthesecondshortestroot,inaccordancetotheresultsofBlack.⁵

Weak positivecorrelationsbetween crown and rootlengthswereobserved only in themandibularcanineand premolars.Thisresultindicatesthattherootlength of patients with malocclusions cannot be estimated accurately from the crown lengthformosttoothtypes.Thecrownmeasurementwas1.04mm longerandthe rootmeasurementwas0.6mm shorterin thepresentstudy whencomparedtothe Kim etal²⁶study on Korean people.This difference mightbe attributable to the factthatKim etal²⁶measuredcrown length perpendiculartothelong axisofthe tooth,whereasitwasmeasuredfrom thecusptiptothebuccalCEJinthepresent study.Theshorterrootsapparentin thepresentstudy mightbeexplained by the factthatthesamplewascomprisedofonlypatientswithmalocclusions.

Hwang and Song²⁷ evaluated root resorption before orthodontic treatment in patientswithmalocclusionsandreportedthatthemaxillary centralincisorwasthe mostsusceptibleto substantialrootresorption.In thepresentstudy,themaxillary rightcentralincisorhad occlusalcontactin 41.9% ofthemalesubjectsand38.7%

of the female subjects. The low percentages of occlusal contact might have

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contributedtotheshortmaxillary centralincisorroot.Toelucidatetherelationship between root length and malocclusions,a comparative study of root length in normalocclusion andmalocclusionsshould beconducted.Furthermore,comparisons amongvarioustypesofmalocclusionsshouldbeundertaken.

A limitationofthisstudyisthatonlyoneHU rangewasusedforreconstructing theCBCT imagesto maintain a constantviewing condition.ThisHU range was chosen to highlightthe differentdensities oftherootapex and surrounding bone withoutdisappearance ofthe rootapex.Ifa higherHU range was chosen,the CBCT-based measurements ofrootlength mighthave been significantly shorter than thedirectmeasurements.Given thattheCBCT-based measurementsoftotal tooth length were significantly shorterthan the directmeasurements,the crown and rootlengthsmay havebeen underestimated.Themeasurementofrootlength is affected by tube voltage and current,voxelsize,and grayscale depth during CBCT imaging and theHU rangeused forimagereconstruction.Furthermore,the appropriate HU range for rootlength measurements can vary greatly when the CBCT scannerorimaging parametersorpositionischangedbecauseHU valuesof CBCT are notreliable.²⁸^,²⁹ The effectofthese factors should be studied in the future.Finally,molarswerenotmeasuredinthepresentstudybecauseoftheneed fordifferentalignmentduring CBCT imaging.Therefore,studies including molar measurementsarealsorequired.

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Ⅴ.Concl usi ons

Inthisstudy,CBCT imageswereobtainedusingaCB MercuRayscannerwitha 0.292-mm voxelsizeand12-bitgrayscaletocomparetotal,crown,androotlengths ofpremolars measured using CBCT and digitalcalipers.Because teeth without metalrestorationswereused asspecimens,theresultscannotbeapplied to teeth withsuchrestorations.Fortotallength,theCBCT measurementsweresignificantly shorterthan thedirectmeasurements,butno significantdifferencesin crown and rootlengths were observed between the methods.Therefore,the nullhypothesis wasrejected forthetotaltooth length measurementsand accepted forthecrown and root length measurements. The method error value of the CBCT-based measurements ofcrown length was similarto the voxelsize used in this study andthatofrootlengthwassomewhatlarger(0.82mm).Inaddition,the95% limits ofagreementwerewiderapartfortherootlength measurementsthan thecrown length measurements.Thedataobtained in thisstudy can beused asareference forevaluating CBCT-based measurements ofrootlength and resorption ofteeth withoutmetalrestorationsinpatientswithmalocclusions.

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Ref er ences

1. BrezniakN,WassersteinA.Orthodonticallyinducedinflammatoryroot resorption.PartI:Thebasicscienceaspects.AngleOrthod2002;72:175-9.

2. SameshimaGT,SinclairPM.Predictingandpreventingrootresorption:PartI. Diagnosticfactors.Am JOrthodDentofacialOrthop2001;119:505-10.

3. LupiJE,HandelmanCS,SadowskyC.Prevalenceandseverityofapicalroot resorptionandalveolarbonelossinorthodonticallytreatedadults.Am JOrthod DentofacialOrthop1996;109:28-37.

4. PletsJH,IsaacsonRJ,SpeidelTM,WormsFW.Maxillarycentralincisorroot lengthinorthodonticallytreatedanduntreatedpatients.AngleOrthod

1974;44:43-7.

5. BlackGV.Descriptiveanatomyofthehumanteeth.Philadelphia,Pa:TheS.S.

WhiteDentalManufacturingCo1902:16-21.

6. VerhoevenJW,VanAkenJ.VanderWeerdt.GP.Thelengthofteeth:A statisticalanalysisofthedifferencesinlengthofhumanteethforradiologic purposes.OralSurgery,OralMedicine,OralPathology1979;47:193-9.

7. MainaSW,WagaiyuCK.TheaveragehumantoothlengthsforblackKenyan population.Eastafricanmedicaljournal1990;67:33-8.

8. BjorndalAM,HendersonWG,SkidmoreAE,KellnerFH.Anatomic

measurementsofhumanteethextractedfrom malesbetweentheagesof17 and21years.OralSurgery,OralMedicine,OralPathology1974;38:791-803.

(22)

- 12 -

9. JayawardenaCK,AbesundaraAP,NanayakkaraDC,ChandrasekaraMS.

Age-relatedchangesincrownandrootlengthinSriLankanSinhalese.Journal oforalscience2009;51:587-92.

10. OzakiT,SatakeT,KanazawaE.Morphologicalsignificanceofrootlength variabilityincomparisonwithothercrowndimensions.I.Basicstatisticsand sexdifference.JNihonUnivSchDent1987;29:233-40.

11. OzakiT,SatakeT,KanazawaE.Morphologicalsignificanceofrootlength variabilityincomparisonwithothercrowndimensions.II.Correlationbetween crownandrootmeasurements.JNihonUnivSchDent1988;30:11-21.

12. BrezniakN,GorenS,ZoiznerR,ShochatT,DinbarA,WassersteinA,Heller M.Theaccuracyofthecementoenameljunctionidentificationonperiapical films.AngleOrthod2004;74:496-500.

13. JakobssonR,LindV.Variationinrootlengthofthepermanentmaxillary centralincisor.ScandJDentRes1973;81:335-8.

14. BrezniakN,GorenS,ZoiznerR,ShochatT,DinbarA,WassersteinA,Heller M.A comparisonofthreemethodstoaccuratelymeasurerootlength.Angle Orthod2004;74:786-91.

15. ThanyakarnC,HansenK,ÅkessonL.Measurementsoftoothlengthin panormaicradiogrphs.1.:Theuseofindicators.Dentomaxillofac.Radio 1992;21:26-30.

16. YassaeiS,Ezoddini-ArdakaniF,OstovarN.Predictingtheactuallengthof premolarteethonthebasisofpanoramicradiology.IndianJDentRes 2010;21:468-73.

(23)

- 13 -

17. LienLC,SohG.Accurayoftheorthopantomogram inassessmentoftooth lengthinorthodonticpatients.SingaporeDentJ2000;23:68-71.

18. HölttäP,Nyström M,EvälahtiM,AlaluusuaS.Rootcrownratiosof permanentteethinahealthyFinnishpopulationassessedfrom panoramic radiographs.EuropeanJournalofOrthodontics2004;26:491-7.

19. StramotasS,GeentyJP,DarendelilerMA,ByloffF,BergerJ,PetoczP.The reliabilityofcrown-rootratio,linearandangularmeasurementonpanoramic radiographs.ClinorthodRes2000;3:182-91.

20. LundH,GröndahlK,GröndahlHG.Conebeam computedtomographyfor assessmentofrootlengthandmarginalbonelevelduringorthodontic treatement.AngleOrthod2010;80:466-73.

21. SherrardJF,Rossouw PE,BensonBW,CarrilloR,BuschangPH.Accuracy andreliabilityoftoothandrootlengthsmeasuredoncone-beam computed tomographs.Am JOrthodDentofacialOrtohop2010;137:S100-8.

22. StratemannSA,HuangJC,MakiK,MillerAJ,HatcherDC.Comparisonof conebeam computedtomographyimagingwithphysicalmeasures.

DentomaxillofacialRadiology2008;37:80-93.

23. PinskyHM,DydaS,PinskyRW,MischKA,SarmentDP.Accuracyof three-dimensionalmeasurementsusingcone-beam CT.Dentomaxillofacial Radiology2006;35:410-16.

24. BaumgaertelS,PalomoJM,PalmoL,HansMG.Reliabilityandaccuracyof cone-beam computedtomographydentalmeasurements.Am JOrthod DentofacialOrthop2009;136:19-28.

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- 14 -

25. PonderSN,BenavidesE,KapilaS,HatchNE.Quantificationofexternalroot resorptionbylow-vshigh-resolutioncone-beam computedtomographyand periapicalradiography:A volumetricandlinearanalysis.Am JOrthod DentofacialOrthop2013;143:77-91.

26. Kim MS,Kim SH,Kim HJ,Kim HJ,ParkKP,ParkBG etal.DentalAnatomy andMorphology.Seoul,Korea:JeesungPublishing;2005:27.

27. HwangCJ,SongYY.A radiographicstudyonrootresorptioninthe malocclusionpatientsbeforeorthodontictreatment.KoreanJorthod 1999;29:219-37.

28. NackaertsO,MaesF,YanH,CoutoSouzaP,PauwelsR,JacobsR.Analysis ofintensityvariabilityinmultisliceandconebeam computedtomography.Clin OralImplRes2011;22:873–9.

29. PauwelsR,NackaertsO,BellaicheN,StamatakisH,TsiklakisK,WalkerA,et al.Variabilityofdentalconebeam CT greyvaluesfordensityestimations.Br JRadiol2013;86:20120135.

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- 15 - Male Mean± SD

Female Mean±SD

Total(n) 31 31

Age(years) 22.4± 3.0 21.2± 3.9 OB (mm) 1.0± 3.5 1.2± 1.3 OJ(mm) 1.1± 5.0 2.9± 2.9 FMA(°) 26.5± 3.0 29.8± 3.3 ANB(°) 0.8± 4.7 2.9± 3.2 Incisorcontact^* 41.9% 38.7%

Tabl es

Table1.Characteristics ofthe subjects forthe CBCT-based incisor,canine,and premolarlengthmeasurements

Valuesarepresentedasnumberasnumberormean± standarddeviation

*Percentageofthepresenceofocclusalcontactonmaxillaryrightcentralincisors. CBCT,Cone-beam computed tomography; OB,Overbite ; OJ,Overjet ; FMA, Frankfortmandibularplaneangle;ANB,ANB angle.

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CBCT Physical Difference Mean SD Mean SD Mean SD P

Toothlength(mm) 21.37 1.56 21.55 1.59 0.18 0.44 <0.001^* Crownlength(mm) 9.07 0.77 9.07 0.81 -0.00 0.46 0.994

Rootlength(mm) 13.10 1.33 13.12 1.36 -0.03 0.61 0.682 Table2.Comparison oftheCBCT-based and directtooth length measurementsof theextractedpremolars

Valuesarepresentedasnumberasnumberormean± standarddiviation

*P< 0.05bythepairedt-test.

CBCT,Cone-beam computedtomography.

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Male Female Mean SD Mean SD P

Toothlength(mm) 22.83 2.55 21.91 2.34 <0.001^* Crownlength(mm) 10.38 1.61 9.97 1.52 0.009^* Rootlength(mm) 13.53 1.77 12.91 1.71 <0.001^* R/C ratio 1.33 0.24 1.32 0.25 0.807 Table3.ComparisonoftheCBCT-basedtoothlengthmeasurementsofthemale andfemalesubjects

Valuesarepresentedasnumberasnumberormean± standarddiviation

*P< 0.05bytheMann-WhitneyU-test.

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- 18 - Toothtype

Male Female

Mean SD Group Mean SD Group Mxcentralincisor 12.30 1.55 B 11.75 1.46 B

Mxlateralincisor 13.25 1.20 B 12.66 1.07 B Mxcanine 15.83 1.49 A 15.23 1.78 A Mxfirstpremolar 13.24 1.30 B 12.40 1.53 B Mxsecondpremolar 13.18 1.72 B 12.55 1.51 B Mncentralincisor 11.56 0.87 C 10.99 0.88 C Mnlateralincisor 12.75 0.95 B 12.58 0.92 B Mncanine 15.02 1.52 A 14.21 1.28 A Mnfirstpremolar 13.77 1.23 B 13.56 1.02 A Mnsecondpremolar 13.58 1.11 B 13.16 1.10 A Table4.CBCT-basedrootlengthmeasurementsoftheincisors,canines,and premolarsbygender

Mx,maxillary;Mn,mandibular.

Meanswiththesamegroupletterarenotsignificantlydifferent. SD,Standarddeviation.

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- 19 -

Fi gur es

Fig1.Schematicofthelandmarksusedformeasuringthetotaltooth,crown,and rootlengthsoftheextractedpremolars.

Fig2A.

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- 20 - Fig2B.

Fig2C.

Fig2D.

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- 21 - Fig2E.

Fig 2. Alignment procedure of multiplanar reconstruction windows for the CBCT-based length measurements.The red,yellow,and blue lines indicate the sagittal,coronal,andaxialplanes,respectively.(A)Theintersection ofthesagittal andcoronalplanesisalignedwiththecenterofthepulpchamberintheaxialview ofthetooth tobemeasured.(B)Thesagittalplaneisrotatedin thecoronalview ofthetooth such thatitpasses through the buccalcusp and roottips.(C)The coronalplane in the sagittalview of the tooth is rotated such that it passes through thebuccalcusp and roottips,whileensuring thatthesagittalplanealso passesthroughthebuccalcuspandroottips.(D)Verificationthatthesagittaland coronalplanes pass through the buccalcusp and roottips by moving the axial slice untilthe cusp orroottip disappears.(E)Measurementofcrown,root,and totaltooth lengths in the sagittalview ofthe tooth.These measurements were performedsimilarlytothecorrespondingdirectmeasurements.

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- 22 - Fig3A.

Fig3B.

Fig3C.

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- 23 -

Fig3.Bland–AltmanplotsoftheCBCT-basedanddirectlengthmeasurementsof theextractedpremolars.TheCBCT-physicaldifference(dottedline),mean

difference(thicksolidline)and95% limitsofagreement(dashedlines)areshown.

(A)Crownlength.(B)Rootlength.(C)Totaltoothlength.