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20 14 년 월2

석사 학위 논문

김 영 재

2014년 2월 석사학위 논문

입천장뼈 두께의

두부방사선사진 계측값과 CBCT 계측값 비교

조 선 대 학 교 대 학 원

치 의 학 과

김 영 재

[UCI]I804:24011-200000264406

(3)

입천장뼈 두께의

Comparison of cephalometric measurements and cone-beam

computed-tomography-based measurements of palatal bone thickness

2014년 2월 25일

치 의 학 과

김 영 재

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입천장뼈 두께의

지도교수 임 성 훈

이 논문을 치의학 석사학위신청 논문으로 제출함

2013년 10월

치 의 학 과

김 영 재

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김영재의 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

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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

--- 11

Re f e r e nc e s

--- 12

Tabl e s

--- 14

Fi gur e s

---18

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표 목 차

TableI. Samplecharacteristics ---14 TableII. Descriptionofreferenceplanesandlandmarks---15 TableIII. Frequencyofencounteringtheincisivecanalormaxillarysinus

alongthemeasurementlineduringCBCT measurements---16 TableIV.Comparisonofpalatalbonethicknessesmeasuredfrom

thecephalogram (ceph)andCBCT images(inmm)---17

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도 목 차

Fig1. Schematicofthemagnificationofpalatalboneat5mm

off-center---18 Fig2. Cephalometricmeasurementsofpalatalbonethickness---19 Fig3. MeasurementofpalatalbonethicknessonaCBCT image---20 Fig4. Bland-Altmanplots:differenceagainstthemeanoftheCBCT

andcephalometricmeasurements---21 Fig5. ComparisonofpalatalbonethicknessesinCBCT-based

measurementsat5mm off-center,7.5mm off-center,

andminimum thickness,andcephalometricmeasurements---22 Fig6. ComparisonofpalatalbonethicknessesinCBCT-based

measurementsat1.5mm off-centerand10mm off-center,

andcephalometricmeasurements---23 Fig7. Changeinnasalcrestheightfrom P1P2toM1M2--- 24

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ABSTRACT

Compar i son ofcephal omet r i cmeasur ement sand

cone-beam comput ed-t omogr aphy-basedmeasur ement sof pal at albonet hi ckness

Young-jaeKim

Advisor:Prof.Sung-Hoon Lim,DDS,MSD,PhD DepartmentofDentistry

GraduateSchoolofChosun University

Introduction:이 연구의 목적은 입천장뼈 두께를 측정하는데 있어 측모두부계측방사 선사진에서의 계측값과 cone-beam computedtomography(CBCT)영상에서의 계측값 사이의 관계를 결정하기 위한 것이다.

Methods:환자 30명의 CBCT 영상과 측모두부계측방사선사진이 사용되었다.입천장 뼈 두께는 전후방적으로 P1P2(제1소구치와 제2소구치 사이)에서 M1M2(제1대구치와 제2대구치 사이)까지 두 영상 방법 모두에서 측정되었고 횡적으로는 1.5 mm off-center에서 10mm off-center까지 CBCT 영상에서만 측정되었다.반복계측분산분석 을 사용하여 두 계측값 간의 차이를 분석하였다.

Results:Bland-Altmanplots에서 5mm off-center에서의 95% limitsofagreement가 가장 작게 나타났다(-0.2±1.7mm).5mm off-center에서의 계측값만이 모든 전후방적 위치에서 두부계측방사선사진에서의 계측값과 통계적으로 유의한 차이를 보이지 않았 다.1.5 mm off-center에서의 계측값은 P2M1 (제2소구치와 제1대구치 사이)에서 M1M2까지만 두부계측방사선사진에서의 계측값보다 더 유의적으로 두껍게 나타났다.

Conclusions:계측된 모든 영역 중에서,5mm off-center에서의 골이 측모두부계측방 사선사진에서의 입천장뼈 형태를 가장 잘 나타낸다.

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Ⅰ.I nt r oduct i on

The palate is a preferred area for orthodontic mini-implant placementbecause there is little danger ofdamaging anatomicalstructures other than the incisive foramen.¹^,²Also,thereisa relatively largebonemassin themedian and flanking regionsofthepalatewithdensesofttissuesonthesurfaceofthehardpalate,thus facilitating theformation ofcompactconnectivetissuesaround thecervicalpartof theimplant.³^,⁴

The most appropriate length for a mini-implant should be determined from measurementsofthepalatalbonethicknesstoensurethatthemaximum thickness of palatalbone is utilized without penetrating the palate.Although cone-beam computedtomography(CBCT)canbeusedtomeasurepalatalbonethickness,Jung etal⁵ and Winsaueretal⁶ suggested thatCBCT needs to be used only in rare casesofborderlinepalatalbonethickness.

A cephalogram can beused tomeasurepalatalbonethickness,butcaremustbe taken due to the presence ofmagnification,which is typically 110%.^7,⁸ Because a cephalogram is a two-dimensional view of a three-dimensional object with a perspective projection,the magnifications of the rightand left structures differ, resulting in an unequaloverlapoftherightand leftstructures.Thelocation ofan object between the X-ray source and the film determines the magnification of image,with structures closerto the X-ray source appearing larger.The distance between thesourceand themidsagittalplaneofthesubjectistypically 1500mm, and thedistancebetween themidsagittalplaneofthesubjectand thedetectoris 150mm,with thecentralray passing through thecenterofthemechanicalporion.

Thehalfofthepalatalbonethatisclosertothesourceisprojectedonthefilm as ifitwerepositioned moreinferiorly and soitappearslargerthan thehalfon the contralateralside.To illustrate the typicalmagnification in the cephalogram of palatalbonethicknessat5mm off-center,considerthefollowing assumptions(see Fig 1):the palatalbone thickness at5 mm off-centeris 5 mm,and the vertical distance from the centralray to the superiorside ofthe palatalbone is 25 mm.

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According tothecalculationofmagnificationillustratedinFig 1,a5mm thickness ofpalatalboneat5mm off-centerwillbeprojected ontothefilm asa thickness of5.7mm,which isamagnificationof114%.Jung etal⁹reportedthatthevertical dimensionson lateralcephalometry reflecttheminimum thicknessofbone,andnot the maximum thickness in the median plane.In thatstudy⁹ the nasalfloors and palates of dry skulls were covered with tinfoil before the radiographs were obtained.In this condition the bony palate willprobably appear thinner in the cephalogram because its apparent thickness willbe determined by the oblique X-rays passing through the tinfoilon the nasalfloorcloserto the X-ray source and thetinfoilon thepalatalsidecloserto thefilm.Covering thenasalfloorand palate with tinfoil from the center to 5 mm off-center will result in 106%

magnification instead of 114% when the same conditions shown in Fig 1 are assumed.

Severalstudies^1,^2,¹⁰^-13 using CBCT orcomputed tomography have found thatthe palatalbone thickness tends to decrease laterally orposteriorly.Wehrbein etal¹⁴ reported that the thicknessof the anterior and median hard palate was 2 mm thickerthan thatshown in lateralcephalograms.Cephalograms may notdepictthe maximum thickness ofmedian palate,^9,¹⁴ butno previous study has investigated whichpartofthepalateinthetransverseaspectisdepictedonthecephalogram.

Thepurposeofthepresentstudy wastotestthenullhypothesisthatthereisno relationship between thepalatalbonethicknessvaluesin varioustransverse areas asmeasuredcephalometricallyandusingCBCT.

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Ⅱ.Mat er i al sandMet hods

This work was approved by the localethics committee ofSchoolofDentistry, Chosun University (CDMDIRB 1218-86). Thirty sets of CBCT images and cephalograms(for15malesand 15females)wereselected from among theCBCT and cephalogram sets obtained from patients in whom CBCT was performed as partofanorthodonticexamination(TableI).Exclusioncriteriaincludedpathological findings,cleft palate,missing teeth or supernumerary teeth,and a history of previous orthodontic treatment. Lateral cephalograms and CBCT images were obtainedonthesameday.

Cephalometricmeasurements

Lateralcephalogramswereobtainedusing an orthopantomograph equippedwith a cephalostat (PM 2002 Proline, Planmeca, Helsinki, Finland). The following parameterswereused forlateralcephalometry:80 kV,12 mA,and exposuretime of1.4–1.6 seconds.Cephalograms were stored in a PACS (picture archiving and communications system) server after scanning the Computed Radiography (CR) cassette. Measurements were performed using STARPACS PiViewSTAR 5.0 (Infinitt,Seoul,Korea).Theocclusalplanewasused asareferenceplaneforboth cephalometric and CBCT-based measurements (Table II).The occlusalplane was determined as the plane passing the incisaledge of the maxillary left central incisorand themesiolingualcusp tipsoftherightand leftmaxillary firstmolars. Average points between the right and left landmarks were used in the cephalometricmeasurements.Lineswerethendrawnthatwereperpendiculartothe occlusalplaneand passed between thefirstand second premolars(P1P2)and the lingualcusps ofsecond premolars (P2),between the second premolars and first molars(P2M1),themesiolingualcuspsoffirstmolars(M1),and between thefirst and second molars(M1M2).In allcasestheaveragepointsbetween therightand

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leftlandmarkswereused.Palatalbonethicknessesweremeasuredalong theselines (TableII;Fig2).

To compare CBCT-based measurements and cephalometric measurements,the cephalometric measurements were converted to a 100% magnification. In the presentstudy,theX-ray sourcetoobjectdistancewas1510mm andtheobjectto film distance was 128 mm,resulting in a magnification of 108.5%.Therefore, conversion to 100% magnification was achieved by dividing the cephalometric measurementsofpalatalbonethicknessby1.085.

Measurementsin CBCT images

CBCT images were obtained using a CBCT scanner (CB MercuRay,Hitachi, Osaka,Japan)with the following parameters:field ofview of149.5 mm × 149.5 mm,120 kV,15 mA,scan timeof9.6 seconds,slicethickness of0.292 mm,and isometric voxel size of 0.292 mm. Measurements from CBCT images were performed using Ondemand3D 1.0 (Cybermed,Seoul,Korea).A presetofwindow leveling (level:805HU,width:2829HU)wasusedtomaintain aconstantviewing condition.Thiswindow leveling ensured thatonly thosevoxelshaving HU values from –609HU to2220HU weredisplayedin theprogram window.A midsagittal reference plane (MSR)was constructed as the plane passing through the crista galli,anterior nasalspine,and posterior nasalspine.Coronalsections thatwere perpendiculartotheocclusalplaneand passing therightand leftP1P2,P2,P2M1, M1,and M1M2 were selected.For each ofthese coronalsections,palatalbone thicknesses were measured along verticalmeasurementlines parallelto the MSR and offsetfrom itby 1.5,5,7.5,and 10 mm (Fig 3);these measurements were labeled as1.5,5,7.5,and 10mm off-center.Theminimum palatalbonethickness wasalsomeasuredwithintherangefrom theMSR to10mm off-center.Theright andleftmeasurementsmadeonCBCT imageswereaveragedforeachpatient.

When the incisive canal or maxillary sinus was encountered along the measurementline,thethicknessvaluewasnotrecorded(TableIII).Incaseswhere

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the maxillary sinus extends medially below the nasalcavity,the palatalbone thickness measurements willbe made from the floorofthe sinus to the inferior surface of the bony palate.Measurements made from the canalor sinus floor cannotbecompared with thecephalometricmeasurementsthataremadefrom the nasalfloor,which isthesameasthesuperiorsurfaceofthebony palate,and so thesemeasurementsweretreatedasmissingvalues.

Statisticalanalysis

Allmeasurementsfor10sampleswererepeatedafter2weeksbyoneexaminer (Y.K.),andDahlberg'sformula¹⁵wasusedtoevaluatethemethoderrorofthe measurements:thiswas0.32mm incephalometricmeasurementsand0.24mm in CBCT-basedmeasurements.Kolmogorov-Smirnovnormalitytestsshowedthatthe dataconformedtoanormaldistributioninallmeasurementareas.Bland-Altman plots^16,¹⁷andrepeated-measuresANOVA wereusedtoexaminetherelationships amongcephalometricmeasurementsandvariousCBCT-basedmeasurements.The resultswereconsideredsignificantatP<0.05.Bland-Altmanplotsweregenerated usingtheMedCalc12.4.0software(MedCalcSoftware,Mariakerke,Belgium),and otheranalyseswereperformedusingSPSS 12.0(SPSS,Chicago,Ill).

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Ⅲ.Resul t s

The incisive canalwas encountered in 60% ofP1P2,13% ofP2,and 3% of P2M1 measurements in CBCT images at1.5 mm off-center.The maxillary sinus was encountered in 57% of 10-mm-off-center measurements and in 20% of 7.5-mm-off-centermeasurements(TableIII).

InBland-Altman plots,thelimitsofagreement(LOA)weredefinedas±1.96SD, andthe95% CIvaluesfortheLOA wereidentified(asmarkedinFig4).The95%

LOA were0.9±3.1 mm (mean±1.96SD)for1.5 mm off-center,–0.2±1.7 mm for5 mm off-center,–0.1±1.9 mm for 7.5 mm off-center,1.6±3.5 mm for 10 mm off-center,and–1.0±1.7mm fortheminimum bonethickness(Fig4).

The cephalometric measurements ofpalatalbone thickness decreased posteriorly from 9.91±2.10 mm atP1P2 to 2.52±1.35 mm atM1M2.The cephalometric and 5-mm-off-centermeasurementsdidnotdiffersignificantlyinanyareas.At7.5mm off-center,there was a significantdifference only in the M1M2 area.At1.5 mm off-center,P2M1,M1,andM1M2measurementsweresignificantly thickerthan the cephalometric measurements.Allmeasurements at 10 mm off-center except for M1M2 measurements were significantly thicker than the cephalometric measurements. Minimum measurements were significantly thinner than the cephalometricmeasurementsinallareasexceptP2M1(TableIV;Figs5and6).

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Ⅳ.Di scussi on

Thenullhypothesiswasrejectedinfavorofanalternatehypothesisthatthereis a strong correlation between cephalometric measurements and CBCT-based measurements of the palate especially at 5 and 7.5 mm off-center (Fig 4).In Bland-Altman plots, 5- and 7.5-mm-off-center measurements showed minimal mean differencesandrelatively smallLOA,with theLOA being smallestat5mm off-center(–0.2±1.7mm).Thisindicatesthattheboneat5mm off-centeristhe mostlikelyareatobedepictedincephalogramsaspalatalbonecontours.

ThehorizontalaxisoftheBland-Altman plotistheaverageofCBCT and100% cephalogram measurements, and this average increases from M1M2 to P1P2 becausethepalatalbonethicknesstendsto increaseanteriorly.TheBland-Altman plotfor10mm off-centershowedpositiveproportionality.Thismay beduetothe difference between 10 mm off-centerand the 100% cephalogram increasing from M1M2 to P1P2 whiletheaveragevalueofthetwo measurements increased from M1M2 to P1P2.The smallestdifference shown atM1M2 mightbe due to the 10-mm-off-centerarea becoming incorporated into the flatterarea atM1M2 and being depicted in the cephalogram as a palatal contour along with the 5-mm-off-centerarea.

The Bland-Altman plotfor1.5 mm off-centershowed negative proportionality.

This may be due to the difference between 1.5 mm off-center and the 100% cephalogram decreasing from M1M2 to P2M1 whiletheaveragevalueofthetwo measurements increased from M1M2 to P2M1.The minimum measurements were significantlythinnerthanthecephalometricmeasurementsinallareasexceptP2M1. When compared tothecephalometricmeasurements,the5- and 7.5-mm-off-center measurements showed no significantdifferences,exceptin the M1M2 area at7.5 mm off-centerwheretheCBCT-basedmeasurementwassignificantlythinner.

Flatareas parallelto the centralray appearmore radiopaque than the curved areas in a cephalogram,owing to the overlapping ofcorticalbone in flatareas. The differences between 5 and 7.5 mm off-center were statistically insignificant

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exceptforthe M1M2 area at7.5 mm off-center,which suggestthatthese areas constituterelatively flatareasofthepalateandaredepictedinthecephalogram as the palatal bone contour except for the M1M2 area at 7.5 mm off-center. Considering that the maxillary sinus was involved in 20% of the 7.5-mm-off-center measurements, cephalograms are most likely to depict the corticalboneinthe5-mm-off-centerareaofthepalate.

Thepresentstudyselectedthe1.5-mm-off-centerarearatherthanthemidpalatal area,because the palatalbone at1.5 mm off-center should be thicker than the lengthofthemini-implantthatistobeinsertedintotheboneifpenetrationofthe palatalboneduring theplacementofthemini-implantisconsidered undesirableor unnecessary.Additionally,determination ofthe superiorend ofthe nasalcrestis difficultbecausethethinvomerboneisattachedoverthenasalcrest.¹

The 1.5-mm-off-center and cephalometric measurements did not differ significantly in the P1P2 and P2 areas, whereas the 1.5-mm-off-center measurements were significantly thicker than the cephalometric measurements in the otherareas.When the nasalcrestheightwas estimated indirectly using the difference in bone thicknesses measured at1.5 and 5 mm off-center,the nasal crest height increased from P2 to M1M2 (Fig 7).Although the cephalometric measurements of palatalbone thicknesses decreased continuously from P1P2 to M1M2,thepalatalbonethicknessesat1.5 mm off-centerwererelatively constant intheP2M1,M1,andM1M2areas.Thiscanbeattributedtotheincreasing height ofthe nasalcrestcompensating for the posteriorly directed gradualdecrease in overall palatal bone thickness in the 1.5-mm-off-center area. Considering the increasing height of the nasal crest (Fig 7), the bone thickness at 1.5 mm off-center can be roughly estimated from the cephalometric measurements by adding 1 and 2 mm to M1- and M1M2-area measurements,respectively.Because thebonethicknessin P1P2and P2areaswasthesamein 1.5-mm-off-centerand 100% cephalogram measurements,and the bone in P2M1 to M1M2 areas was thicker for 1.5-mm-off-center measurements than for the 100% cephalograms, CBCT may notbeneeded when planning mini-implantplacementin themidpalate when cephalograms exhibit sufficient bone thickness.However,if cephalograms

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show very thin palatalbone,then CBCT may berequired to evaluatetheprecise bonethicknessofthemidpalateand nasalcrest,ortoexploreothersuitableareas formini-implantplacement.

Among 1.5-mm-off-centermeasurements,60% ofP1P2 measurements and 13% of the P2 measurements encountered the incisive canal. Therefore, placing mini-implants using the fullthickness ofthe P1P2 or P2 midpalatalbone may result in involvement of the incisive canal. Also, the maxillary sinus was encountered in 7–17% and 0–7% of10- and 7.5-mm-off-center measurements, respectively. Caution is required when placing mini-implants in these areas. BecausethepresentstudyincludedCBCT-basedmeasurementsthatdidnotinvolve themaxillary sinusorincisivecanal,thepalatalboneofan actualpatientcan be thinnerthan the mean values obtained in the presentstudy,especially when the maxillary sinusextendsmedially below thenasalfloororwhen theincisivecanal ispositionedovertheP1P2area.Thepalatalbonewasfoundtobethickestin the P1P2 area;however,in this area 60% of the 1.5-mm-off-center measurements encountered the incisive canal,and 7% of the 10-mm-off-center measurements encountered the maxillary sinus. Therefore, the area between 5 and 7.5 mm off-centercan besaferwhileproviding similarquantity ofpalatalbone—theremay beathinnermucosaandbetterbonequalityinthemidpalatalareas.

Possible limitations to this study mustbe considered.Although there were no significant differences between 5-mm-off-center and 100% cephalogram measurements,this does not mean that the palatal bone thickness at 5 mm off-centercanbeaccuratelymeasuredusing thecephalogram.Althoughtheboneat 5mm off-centermaybedepictedincephalogramsaspalatalbonecontoursinmost cases,there could be large interindividualvariations.The characteristics of the depicted area willvary with the width of the palate.Also,a deep palate or V-shaped arch may show lessflatareas,resulting in blurring ofthepalatalbone contouron thecephalogram.When thereisaverticaldifferencebetween theright and leftsides ofthe palatalbone,or when there is verticalasymmetry ofthe externalauditory meatuscausing misalignmentofthehead and palate,thepalatal bonethicknessshown on thecephalogram can beexaggeratedwith someblurring.

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Thepresenceofthepalatalbonewith ablurred contouron acephalogram means thatcephalometricmeasurementsofthepalatalbonethicknessshould notbeused as a guide for mini-implantplacement.The CBCT-based measurements of the palate reported herein may be used as a guideline for planning mini-implant placementinthepalate.However,largeinterindividualvariationsinthepalatalbone contourandthicknessstillneedtobeconsidered.

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Ⅴ.Concl usi ons

Amongtheareasmeasuredinthepresentstudy,thepalatalboneat5mm off-center is mostlikely to bedepicted in cephalogramsaspalatalbone contours.Thickerbone existsat1.5mm off-centerthanisshownoncephalogramsintheareasfrom P2M1to M1M2owing totheincreasingheightofthenasalcrest.

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17.BlandJM,AltmanDG.Applyingtherightstatistics:analysesofmeasurement studies.UltrasoundObstetGynecol2003;22:85-93.

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Males(n=15) Females(n=15) Mean SD Mean SD Age(years) 19.6 3.4 19.7 3.8 ANB (°) 1.2 5.1 3.1 3.7 FMA (°) 26.5 4.7 28.0 4.1 ICW (mm) 36.0 2.6 35.7 2.1 IMW (mm) 38.7 3.2 38.2 3.3

Tabl es

TableI.Samplecharacteristics

ICW: intercanine width; IMW: intermolar width, the distance between the maxillary firstmolars as measured atthe pointofthe intersection ofthe lingual groovewiththegingivalmargin

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Plane/landmark Definition

Occlusalplane

A plane passing the incisaledge of the maxillary left centralincisorand cusp tips ofthe mesiolingualcusps of bothmaxillaryfirstmolars

MSR plane* A planeconstructed using thecrista galli,anteriornasal spine,andposteriornasalspine

P1P2 Contactpointofthemaxillaryfirstandsecondpremolars P2 Lingualcusptipofthemaxillarysecondpremolar

P2M1 Contactpointofthemaxillary second premolarand first molar

M1 Mesiolingualcusptipofthemaxillaryfirstmolar M1M2 Contactpointofthefirstandsecondmolars TableII.Descriptionofreferenceplanesandlandmarks

*UsedonlyfortheCBCT-basedmeasurements

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- 16 - 1.5mm

off-center

5mm off-center

7.5mm off-center

10mm off-center P1P2 Canal 18(60%) 1(3%)

Sinus 2(7%)

P2 Canal 4(13%)

Sinus 2(7%) 5(17%)

P2M1 Canal 1(3%)

Sinus 2(7%) 4(13%)

M1 Canal

Sinus 1(3%) 4(13%)

M1M2 Canal

Sinus 1(3%) 2(7%)

TableIII.Frequencyofencounteringtheincisivecanalormaxillarysinusalong the measurementlineduringCBCT measurements

Percentage values correspond to the numberofencounters divided by the total numberofsamples.

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P1P2 P2 P2M1

n Mean SD Subgroup n Mean SD Subgroup n Mean SD Subgroup 100% ceph 30 9.91 2.10 bc 30 6.42 2.02 bc 30 4.42 1.79 c 1.5mm off-center 12 9.90 3.28 bc 26 5.60 1.37 bc 29 4.75 1.12 b 5mm off-center 29 9.54 2.33 c 30 5.84 2.08 c 30 4.33 1.83 c 7.5mm off-center 30 10.41 2.51 b 28 5.98 2.04 b 28 4.13 1.59 c 10mm off-center 28 12.91 2.72 a 25 8.26 2.65 a 26 6.05 2.31 a Minimum 30 8.62 2.37 d 30 4.95 1.95 d 30 3.61 1.54 c

M1 M1M2

n Mean SD Subgroup n Mean SD Subgroup 100% ceph 30 3.25 1.42 b 30 2.52 1.35 b 1.5mm off-center 30 4.43 1.12 a 30 4.86 1.10 a 5mm off-center 30 3.21 1.44 b 30 2.54 1.29 b 7.5mm off-center 29 3.02 1.48 b 29 2.09 1.21 c 10mm off-center 26 3.99 1.46 a 28 2.40 1.10 b Minimum 30 2.47 1.45 c 30 1.77 1.07 d

TableIV.Comparison ofpalatalbonethicknessesmeasured from thecephalogram (ceph)andCBCT images(inmm)

*Measurements with the same subgroup letter do not differ significantly for multiplecomparisons.

TableIV.Continued.

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Fi gur es

Fig1.Schematicofthemagnificationofpalatalboneat5mm off-center.A bone thicknessof5mm atthe5-mm-off-centerareawillbeprojectedontothefilm as a5.7-mm bonethickness.

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Fig2.Cephalometricmeasurementsofpalatalbonethickness.Thethicknessvalues weremeasuredalonglinesdrawnperpendiculartotheocclusalplaneandpassing throughit.

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Fig3.MeasurementofpalatalbonethicknessonaCBCT image.Incoronal sections,palatalbonethicknessesweremeasuredalongverticalmeasurementlines paralleltotheMSR andoffsetfrom itby1.5,5,7.5,and10mm.

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Fig4.Bland-Altmanplots:differenceagainstthemean(thicksolidmiddleblue line)oftheCBCT andcephalometric(ceph)measurements.TheLOA (dashed brownlines),95% CIoftheLOA (thinsolidbluelines),andregressionlines (dashedpinklines)areshown.A,1.5-mm-off-centermeasurements;B, 5-mm-off-centermeasurements;C,7.5-mm-off-centermeasurements;D,

10-mm-off-centermeasurements;andE,minimum-bone-thicknessmeasurements.

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Fig5.ComparisonofpalatalbonethicknessesinCBCT-basedmeasurementsat5 mm off-center,7.5mm off-center,andminimum thickness,andcephalometric measurements.

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Fig6.ComparisonofpalatalbonethicknessesinCBCT-basedmeasurementsat1.5 mm off-centerand10mm off-center,andcephalometricmeasurements.

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Fig7.Changeinnasalcrestheightfrom P1P2toM1M2.Nasalcrestheightswere estimatedindirectlyasthebonethicknessat1.5mm off-centerminusthebone thicknessat5mm off-center.DataaremeanandSD values.