Soft tissue stability after segmental distraction of the anterior mandibular alveolar process: a 5.5 year follow-up

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Article

Reference

Soft tissue stability after segmental distraction of the anterior mandibular alveolar process: a 5.5 year follow-up

JOSS, C U, et al.

Abstract

Soft tissue changes were analysed retrospectively in 17 patients following distraction osteogenesis (DO) of the mandibular anterior alveolar process. Lateral cephalograms were traced by hand, digitized, superimposed, and evaluated at T1 (17.0 days), after DO at T2 (mean 6.5 days), at T3 (mean 24.4 days), at T4 (mean 2.0 years), and at T5 (mean 5.5 years). Statistical analysis was carried out using Kolmogorov-Smirnov test, paired t-test, Pearson's correlation coefficient, and linear backward regression analysis. 5.5 years postoperatively, the net effect for the soft tissue at point B' was 88% of the advancement at point B while the lower lip (labrale inferior) followed the advancement of incision inferior to 24%. Increased preoperative age was correlated (p

JOSS, C U, et al . Soft tissue stability after segmental distraction of the anterior mandibular alveolar process: a 5.5 year follow-up. International Journal of Oral and Maxillofacial Surgery , 2013, vol. 42, no. 3, p. 345-51

DOI : 10.1016/j.ijom.2012.10.020 PMID : 23182400

Available at:

http://archive-ouverte.unige.ch/unige:29129

Disclaimer: layout of this document may differ from the published version.

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Clinical Paper Orthognathic Surgery

Soft tissue stability after

segmental distraction of the anterior mandibular alveolar process: a 5.5 year follow-up

C. U. Joss,A. Triaca,M. Antonini,S. Kiliaridis,A.M. Kuijpers-Jagtman:Soft tissuestabilityaftersegmentaldistractionoftheanteriormandibularalveolar process:a5.5yearfollow-up. Int.J.OralMaxillofac.Surg.2013;42:345–351.

#2012InternationalAssociationofOralandMaxillofacialSurgeons.Publishedby ElsevierLtd.Allrightsreserved.

C.U.Joss^1,2,A.Triaca³, M.Antonini³,S.Kiliaridis², A.M.Kuijpers-Jagtman¹

1DepartmentofOrthodonticsandCraniofacial Biology,RadboudUniversityNijmegen MedicalCentre,Nijmegen,TheNetherlands;

2DepartmentofOrthodontics,Universityof Geneva,Switzerland;³PyramideKlinik, Zu¨rich,Switzerland

Abstract. Softtissuechangeswereanalysedretrospectivelyin17patientsfollowing distractionosteogenesis(DO)ofthemandibularanterioralveolarprocess.Lateral cephalogramsweretracedbyhand,digitized,superimposed,andevaluatedatT1 (17.0days),afterDOatT2(mean6.5days),atT3(mean24.4days),atT4(mean2.0 years),andatT5(mean5.5years).Statisticalanalysiswascarriedoutusing Kolmogorov–Smirnovtest,pairedt-test,Pearson’scorrelationcoefficient,and linearbackwardregressionanalysis.5.5yearspostoperatively,theneteffectforthe softtissueatpointB⁰was88%oftheadvancementatpointBwhilethelowerlip (labraleinferior)followedtheadvancementofincisioninferiorto24%.Increased preoperativeagewascorrelated(p<0.05)withmorehorizontalbackward movement(T5–T3)forlabraleinferiorandpogonion⁰.HigherNL/ML⁰angleswere significantlycorrelated(p<0.05)tosmallerhorizontalsofttissuechangeatlabrale inferior(T5–T3).TheamountofadvancementatpointBwassignificantly correlatedwithanupwardmovement(T5–T3)oflabraleinferior(p<0.01)and stomioninferior(p<0.05).Itcanbeconcludedthatfurtherchangeinsofttissues occurredbetween2.0and5.5yearspostoperatively.Thephysiologicalprocessof ageingandlossofsofttissueelasticityshouldbeconsideredaspossiblereasons.

Keywords: distractionosteogenesis;softtissue stability; soft tissue to hard tissue ratio; soft tissue change;cephalometry; mandibularadvancement.

Acceptedforpublication19October2012 Availableonline20November2012

Thecombinationoforthodontictreatment andmaxillofacialsurgeryaimstoprovide optimal function and the best aesthetic resultsforthepatient.Theclinicianneeds preciseinformationtoincreasehisability to predict the surgical effect of skeletal displacement on the patient’s overlying soft tissueprofile.Commonly,ina two-

dimensional analysis the amount of change necessaryto provide appropriate softtissueprofilechangebymaxillofacial surgeryisdeterminedbytheuseofratios betweenthesofttissuesandtheunderlying skeletalanddentalbase.

Littleisknownabouttheeffectofman- dibular DOon the change in shapeand

positionofthesofttissueprofile^1–3when compared with bilateral sagittal split osteotomy (BSSO) for mandibular advancement.^4–9 Commonly used lateral cephalograms canonlyreproduceatwo- dimensionalpre-andpostoperativesitua- tionwhereasinrecentyearstherehasbeen a trend in quantifyingsoft tissueprofile

http://dx.doi.org/10.1016/j.ijom.2012.10.020,availableonlineathttp://www.sciencedirect.com

0901-5027/030345+07$36.00/0 #2012InternationalAssociationofOralandMaxillofacialSurgeons.PublishedbyElsevierLtd.Allrightsreserved.

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changes using three-dimensional evaluation(i.e.opticallasersurfacescanners,¹⁰ stereophotogrammetrywithcameras,¹¹or computed tomography assisted ima- ging¹²).

Recently, skeletal and soft tissue changes2yearsafter DOoftheanterior mandibular alveolar segment have been examined.^2,13,14Theneteffectofthesoft tissue at point B⁰ was 100% of the advancement at pointBwhile thelower lip(labraleinferior)followedtheadvance- mentofincisioninferiorto46%examined 2.0yearspostoperatively.¹³Skeletally,5.5 years after DO the horizontal backward relapse measured 0.3mm or 8.3% at pointBand1.8mmor29.0%atincision inferior.¹⁴ To the authors’ knowledge, evaluation of the soft tissue profile and itschangeinthelong-termislacking.The aimofthepresentstudywastoevaluate softtissuechanges5yearsaftertreatment in adult patients treatedwith DOof the anterior mandibularalveolarprocess and torelateittodifferentparameters.

Materialsandmethods

The study represents a follow-up of an initial sample of 33 patients published previously.^2,13 Theinitialpatientsample consisted of 33 Caucasian patients (27 females and six males) aged 16.5–56.0 years (mean age 30.3 years, SD 10.7).

Of these 33 patients, 17 patients could be re-examined. The follow-up group (T1) consisted of 17 Caucasian patients (14femalesandthreemales);aged16.5–

56.0years(meanage29.8years,SD11.9).

Ethical approval was obtained from the ethic committee of the Kanton Zu¨rich, Switzerland (number 593). All subjects gavewritten,informedconsent.

All patients were treated orthodonti- callybyoneorthodontist(MA)andunder- went DO of the anterior mandibular alveolarprocesstocorrectaskeletalClass IIandlargeoverjetwithorwithoutincisor crowdingatthePyramideClinicinZu¨rich, Switzerlandintheyears1998–2004.The femalepatientsinthefollow-upgrouphad ameanageof31.7years(17.1–56.0years, SD12.0years)andthemalepatients21.5 years (16.5–31.4years, SD8.6years) at T1.Thesurgicalprocedurewasperformed byoneexperiencedmaxillofacialsurgeon (AT); the technique has been published previously.^15,16 Patients receiving other surgical procedures simultaneously on themandibleandmaxilla,suchasgenio- plasty,BSSO,andLeFort,wereexcluded.

Syndromic or medically compromised patients were excluded. Five cephalograms were taken: the first on average

17.0daysbeforesurgery(T1);thesecond (T2) between 0 and 12 days (mean 6.5 days)aftertheosteotomyandbeforeany distractionwascarriedout;thethird(T3) between13and92days(mean24.4days);

thefourth(T4)between0.9and3.7years (mean 2.0 years), and the fifth (T5) between 2.7 and 8.3 years (mean 5.5 years) after distraction of the anterior mandibularalveolarprocess.Thedistrac- tionwas completedatT3 andtheortho- dontictreatmentatT4.Thepositionofthe lowerincisorswasretainedwithabonded onlyoncaninetocanineretainer.TheDO procedure has been described previously.^15,16

Cephalometricanalysis

Soft tissue changes were evaluated on profile cephalograms taken with the teeth in the intercuspal position, and including a linear enlargement of1.2%.

The cephalograms were taken with the subject standing upright in the natural headpositionandwithrelaxedlips. The sameX-raymachineandthesamesettings wereusedtoobtainallcephalograms.

Thelateralcephalogramswerescanned and evaluated with the Viewbox 3.1¹ program(dHalsoftware,Kifissia,Greece).

Theconventionalcephalometricanalysis forT1,T2,T3,T4,andT5wascarriedout by one author (CUJ) and included the reference points and lines shown in Fig.1. Horizontal(x-values)andvertical (y-values) linear measurements were obtained by superimposing the tracings of the different stages (T2, T3, T4 and T5)onthefirstradiograph(T1), andthe reference lines were transferred to each consecutivetracing.Duringsuperimposi- tion,particularattentionwasgiventofit- tingthetracingsofthecribriformplateand the anterior wall of the sella turcica which undergo minimal remodelling.¹⁷ 346 Jossetal.

Fig.1. Referencepointsandlinesusedinthecephalometricanalysis.Thecoordinatesystem haditsoriginatpointS(sella),anditsx-axisformedanangleof78withthereferencelineNSL.

G,glabella;S,sella;NSL,nasion-sella-line;N,nasion;x,horizontalreferenceplane;NL,nasal line; Cm,columella;Sn,subnasale;ILs, upperincisal line;Ans,anteriornasalspine; Pns, posterior nasalspine;As,apexsuperior;pointA;pointA⁰,softtissuepointA;Ls,Labrale superior;Ss,stomionsuperior;Ii,incisioninferior;Is,incisionsuperior;Si,stomioninferior;Li, labraleinferior;Go,gonion;ML⁰,mandibularlineprime;Ai,apexinferior;pointB;pointB⁰, softtissuepointB;Pg,pogonion;Pg⁰,softtissuepogonion;Me,menton;Me⁰,softtissuementon;

S-Line;andy,verticalreferenceplane.

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Atemplateoftheoutlineofthemandible ofthepreoperativecephalogram(T1)was madetominimizeerrorsforsuperimpos- ingonsubsequentradiographs.

Conventionalcephalometricvariablesas well as the coordinates of the reference pointswerecalculatedbythecomputerpro- gram.Thecoordinatesystemhaditsoriginat pointS(Sella),anditsx-axisformedanangle of78withthereferencelineNSL(Fig.1).

Overjetandoverbitewerecalculatedfrom the coordinates of the points Is (incision superior)andIi(incisioninferior).

The lateral cephalograms of T2 were only used to locate the cephalometric point,calledthealveolarsurgicalanterior base(Asab)beforepostoperativedistrac- tion of the alveolar process was carried out.Asabisthemostanteriorandinferior pointoftheloweranteriorsegmentresult- ingfromthesurgicalosteotomy(Fig.2).

Thiscephalometricpointwas introduced to evaluate the movement (rotation vs.

translation)oftheloweranteriorsegment baseincomparisontothelowerincisorsas theratio ^Iiðx-value; T3T2Þ

Asabðx-value; T3T2Þ

Errorofthemethod

Todeterminetheerrorofthemethod,21 randomlyselectedcephalogramswerere- traced and re-analysed after a 2 week interval.Horizontal(x-values)andvertical (y-values) linear measurements were re- obtainedbysuperimposingthetracingsof thedifferentstages(T2,T3,T4andT5)on thefirstradiograph(T1).Theerrorofthe method (si) was calculated with the formula si¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Pd²=2n q

whered is the differencebetweentherepeatedmeasure- ments and n is the number ofduplicate determinations.¹⁸

Statisticalanalysis

Statisticalanalyseswereconductedusing SPSSsoftware(version 19.0,SPSSInc., Chicago, IL, USA). Normal distribution was confirmed with the Kolmogorov–

Smirnov test. The effect of treatment (i.e.thedifferencesbetweenthevariables andco-ordinatesatT3andT1,T5andT1, T5andT3,T5andT4)wastestedwitha paired t-test. The relationships between soft tissue and skeletal variables, age, andgenderwereanalysedwiththePear- son’sproduct momentcorrelationcoeffi- cient and linear backward regression analysis. The drop-outanalysis included the unpaired t-test tocompare drop-outs with the remaining patients for age and cephalometricfeaturesatT1,T2,T3and T4,andthex²testforgenderandage.

Results

Errorofthemethodanddrop-out analysis

TherandomerrorsarepresentedinTable 1. The measurement of the nasiolabial

angle(Cm–Sn–Ls)andmenton⁰(x-value) were excluded dueto theincreased ran- dom error. No systematic errors were found when the values were evaluated withapairedttest.

No significant differenceswere found betweenthedrop-outsandtheremaining patientsforage,genderandcephalometric featuresatT1,T2,T3 andT4.

Horizontalandverticalchanges

Table2showsthedescriptivestatisticsfor theselectedcephalometricvariablesatT1 and T5. The mean changes, standard deviations, and ranges (horizontal and verticaldirection)beforesurgeryanddur- ingthesubsequentobservationperiodsare giveninTables3and4.

Negativevaluesimplyabackward,and positive values a forward, movement of thepointinthehorizontalplane.Negative values imply an upward, and positive values a downward, movement of the pointintheverticalplane.

Softtohardtissueratios

Theneteffect(T5–T1)inlabraleinferior was 24%oftheadvancementinincision inferior. The corresponding value for point B⁰ to point B was 88% and for labralesuperiortoincisioninferior11%.

Correlationsandlinearregression In the period T5–T3, an increase in the patient’sage wassignificantly correlated withadownwardmovementofthevertical or y-value of pogonion⁰ (p=0.014;

R=0.538). Increased patient’s age was significantly correlated to a backward movement of the horizontal or x-values oflabraleinferior(p=0.045;R=0.492) andpogonion⁰(p=0.036;R=0.512)in theperiodT5–T3.

Softtissuestabilityafterdistractionosteogenesis

Fig.2. ReferencepointsusedinthecephalometricanalysisofthelowerapicalbaseinDO patients.Ii,incisioninferior;pointB;Ai,apexinferior;Asab,apicalsurgicalanteriorbase;Pg, pogonion;andMe,menton.Asabisthemostanteriorandinferiorpointoftheloweranterior segmentresultedbythesurgicalosteotomy;thereasonforitsintroductionisgiveninthetext.

Table1. Randomerrors(Si)ofthecephalometriclandmarksandvariables.

Variable Si Variable Si Referencepoint Si(mm)

X Y

SNA(8) 1.14 Overjet(mm) 0.36 Incisionsup. 0.48 0.21

SNB(8) 0.82 Overbite(mm) 0.53 Incisioninf. 0.58 0.55

ANB(8) 0.48 Cm–Sn–Ls(8) 3.32 PointB 0.28 0.45

NSL/NL(8) 0.86 G–Sn–Pg⁰(8) 1.14 Asab 0.35 0.25

NSL/ML⁰(8) 1.01 Ls/Cm–Pg⁰(mm) 0.67 Pogonion 0.37 1.19

NL/ML⁰(8) 0.84 Li/Cm–Pg⁰(mm) 0.49 Menton 0.89 0.45

IsL/NSL(8) 1.52 Labralesup. 0.78 1.30

IsL/NL(8) 1.31 Stomionsup. 1.68 0.99

IiL/ML⁰(8) 1.39 Labraleinf. 1.07 1.01

IsL/IiL(8) 1.63 Stomioninf. 1.15 0.85

PointB⁰ 1.20 1.10

Pogonion⁰ 1.19 1.15

Menton⁰ 3.07 1.21

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Theamountofadvancement(T3–T1,x- value)atpointBwassignificantlycorre- lated to an upward movement of the y- values of labrale inferior (p=0.006;

R=0.637) and stomion inferior (p=0.019; R=0.561). Theamount of

advancement(T3–T1,x-value)atincision inferior and the ratio ^Iiðx-value; T3T2Þ

Asabðx-value; T3T2Þ

was not significantly correlated to the amount of change (T4–T3, x- and y- values)measuredatsofttissuepoints.

A preoperative larger NL/ML⁰ angle (T1) was significantly correlated (p=0.044;R=0.494)withasmallerhor- izontalchangeatlabraleinferior(T5–T3, x-value).Nosignificantcorrelationswere 348 Jossetal.

Table2. ValuesofselectedcephalometricvariablesatT1(beforesurgery)andT5(5.5yearsaftersurgery).

Variable T1 T5

Mean SD Range Mean SD Range

SNA(8) 80.9 3.7 73.1–85.7 80.0 2.8 74.0–84.4

SNB(8) 76.7 4.2 69.8–83.8 77.3 3.8 70.7–85.5

ANB(8) 4.2 2.2 0.3–7.1 2.7 3.0 2.9to6.3

NSL/NL(8) 7.4 4.1 1.9to15.0 7.6 3.7 0.1–13.0

NSL/ML⁰(8) 33.6 7.9 21.4–53.7 34.7 7.1 23.9–53.7

NL/ML⁰(8) 26.2 6.4 16.2–44.8 27.1 5.8 19.8–45.2

IsL/NSL(8) 109.3 9.8 81.7–120.5 105.0 7.1 91.3–117.0

IsL/NL(8) 116.7 9.4 91.0–126.7 112.6 6.2 99.0–121.8

IiL/ML⁰(8) 91.0 6.8 77.2–104.6 96.5 6.6 81.5–108.3

IsL/IiL(8) 126.2 14.0 106.9–157.3 123.8 6.6 81.5–108.3

Overjet(mm) 7.7 2.1 4.5–11.9 2.8 0.9 1.3–4.5

Overbite(mm) 4.4 1.7 1.0–7.3 3.0 1.5 0.2–5.5

Facialconvexity(8) 15.3 6.9 6.4–32.0 13.2 6.6 3.3to29.0

UpperliptoS-line(mm) 2.3 2.7 8.0to2.4 5.0 3.1 9.6to0.8

LowerliptoS-line(mm) 1.9 3.7 8.5to3.2 3.4 3.3 7.7to3.6

Facialconvexity,G–Sn–Pg⁰;upperliptoS-line,Ls/Cm–Pg⁰;lowerliptoS-line,Li/Cm–Pg⁰.

Table3. Changes(mmor8)inthevariablesandco-ordinatesofthemandibleandlowerincisorsastheimmediate(T3–T1)andfinal(T5–T1)result ofDOsurgery.

Variableorcoordinate T3–T1^a T5–T1^b

Mean p SD Range Mean p SD Range

Horizontal

x-Value(mm) Incisionsup. 1.1 ^** 1.4 1.3to3.2 0.4 ns 1.9 4.1to3.0

Incisioninf. 6.2 ^*** 2.5 0.5to10.9 4.6 ^*** 3.2 1.6to11.5

PointB 3.6 ^*** 2.0 0.21to7.6 3.2 ^*** 2.3 0.2to7.3

Asab 2.2 ^*** 2.1 1.1to5.4 1.2 ^* 2.1 2.2to4.7

Pogonion 0.1 ns 1.0 1.7to1.8 0.5 ^* 1.0 0.8to2.4

Labralesup. 0.9 ^* 1.4 1.3to3.8 0.5 ns 1.3 2.8to1.7

Labraleinf. 3.8 ^*** 2.6 0.1–8.7 1.1 ns 2.2 2.4to5.7

PointB⁰ 5.4 ^*** 2.1 1.9–10.5 2.8 ^*** 2.2 1.1to7.7

Pogonion⁰ 4.9 ^*** 1.9 1.5–8.6 3.0 ^*** 2.3 0.6to7.3

Menton⁰ 4.6 ^*** 2.9 0.3to8.6 3.8 ^*** 2.7 0.7to8.8

Vertical

y-Value(mm) Labralesup. 1.4 ^* 2.1 2.6to6.2 0.6 ns 1.5 2.9to1.9

Stomionsup. 0.6 ns 1.7 4.5to1.7 0.8 ^* 1.3 1.1to2.9

Labraleinf. 0.7 ns 2.1 2.8to4.2 0.2 ns 2.3 4.8to3.4

Stomioninf. 0.5 ns 2.2 3.6to7.2 0.3 ns 1.6 3.8to2.6

PointB⁰ 3.5 ^*** 3.3 3.5to8.2 2.6 ^** 3.3 2.8to7.3

Pogonion⁰ 0.2 ns 3.3 6.9to5.8 0.2 ns 4.6 9.7to8.5

Menton⁰ 0.9 ns 2.2 3.9to4.7 0.5 ns 2.6 3.6to5.5

Angular(8)andlinearmeasurements(mm)

Facialconvexity 3.3 ^*** 3.3 7.8to3.7 2.0 ^*** 2.0 7.2to0.9

LstoS-line 1.1 ^** 1.4 4.2to1.2 2.6 ^*** 1.5 5.4to0.2

LitoS-line 0.8 ns 2.1 2.5to4.4 1.5 ^** 1.7 4.0to1.5

Ii/Asab 1.8 7.5 22.4to9.7

Negativevaluesimplyabackwardandpositivevaluesaforwardmovementofthepointinthehorizontalplane.Intheverticalplane,negative valuesimplyanupwardandpositivevaluesadownwardmovementofthepoint.

T1,beforesurgery;T3,24.4daysaftersurgery;T5,5.5yearsaftersurgery.

aT3–T2forAsab,Ii(x-value,T3–T2)/Asab(x-value,T3–T2)insteadmeanvaluethemedianwastakenforthisratioandnopairedt-testwas possiblebecausemeasuredonasingleoccasion.

bT5–T2forAsab.

* p0.05.

** p0.01.

***p0.001.

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foundbetweenthechangeatT5–T3ofall softtissuepointsandgender.

Correlations were significant between horizontal (x-value) hard to soft tissue movements for point B and point B⁰ (T3–T1: p=0.003; R=0.681; T5–T3:

p=0.017;R=0.569),forincisioninferior and labrale inferior (T3–T1: p=0.005;

R=0.649;T5–T3:p=0.092;R=0.422), for incision inferiorand labralesuperior (T3–T1: p=0.067; R=0.454; T5–T3:

p=0.012;R=0.592).

Resultsforthelinearregressionanalysis areshowninTables5and6.

Discussion

Thisresearchrepresentsthecontinuation oftheauthors’previousstudies^2,13onsoft

tissuechangesinpatientsundergoingDO of the anterior mandibular alveolarpro- cess.Auniformgroupof17patientswas obtainedaspatientswithadditionalsurgi- cal procedures of the mandible (genio- plasty, BSSO) and maxilla were excluded.Anevaluationofalveolarseg- mentalDOwithouttheinfluenceofother confoundingsurgicalprocedureswasthus possible. Theeffectofgrowthasa con- foundingfactorwasexcludedbyexamin- ingonlyskeletallymaturepatients(mean age 30.3 years, SD 10.7). An inherent problem of long-termstudies is the loss of patients for follow-up examinations.

Theauthorsperformedadrop-outanalysis for all patients for whom they had no recordsatT5bycomparingtheircephalo- metric variables at all other time points

withtheremainingpatients.Theanalysis showedthatthedropoutsandtheremain- ingpatientswerecomparable,minimizing the risk of bias due to patients lost to follow-up.

Inthepresentstudyon17patients,point B⁰followedpointBto88%andlowerlip (labraleinferior)theadvancementofinci- sioninferiorto24%.Intheauthors’pre- vious study on 33 patients 2.0 years postoperatively,theneteffectofthesoft tissue at point B⁰ was 100% of the advancement at pointBwhile thelower lip(labraleinferior)followedtheadvance- ment of incision inferior to 46%.¹³ The effectsofageingandsofttissueelasticity have to be considered when analysing long-termeffectsofmaxillofacialsurgery on the lipsand chin. In hislongitudinal Softtissuestabilityafterdistractionosteogenesis Table4. Changes(mm,8orratio)inthevariablesandcoordinatesofthemandibleandlowerincisorsastherelapse(T5–T3)andthelong-term change(T5–T4)ofDOsurgery.

Variableorcoordinate T5–T3 T5–T4

Mean p SD Range Mean p SD Range

Horizontal

x-Value(mm) Incisionsup. 1.5 ^** 1.7 5.4to1.2 0.1 ns 0.6 1.6to0.9

Incisioninf. 1.8 ^*** 1.9 5.4to0.6 0.2 ns 0.6 1.6to1.4

PointB 0.3 ns 1.3 2.7to3.3 0.3 ns 0.7 1.0to2.0

Asab 1.0 ^*** 0.9 2.4to1.1 0.1 ns 0.6 1.1to1.5

Pogonion 0.4 ns 1.0 1.6to2.9 0.1 ns 0.7 1.0to2.0

Labralesup. 1.3 ^** 1.8 4.5to2.9 0.2 ns 0.7 1.4to1.7

Labraleinf. 2.7 ^*** 2.0 9.2to0.4 0.6 ns 1.2 72.9to1.4

PointB⁰ 2.7 ^*** 1.4 5.0to0.6 0.3 ns 0.9 1.9to1.0

Pogonion⁰ 1.9 ^*** 1.8 6.8to1.5 0.1 ns 1.1 2.1to2.1

Menton⁰ 0.8 ns 2.5 7.9to2.9 0.5 ns 2.6 4.2to4.8

Vertical

y-Value(mm) Labralesup. 2.0 ^*** 1.8 5.2to1.1 1.0 ^* 1.6 3.3to2.2

Stomionsup. 1.4 ^*** 1.4 0.6to5.1 0.7 ^* 1.1 1.6to3.0

Labraleinf. 0.9 ns 2.5 6.3to2.5 1.0 ns 2.9 6.4to4.2

Stomioninf. 0.2 ns 2.4 5.4to2.6 0.4 ns 2.2 5.8to3.1

PointB⁰ 1.0 ns 2.0 5.3to2.3 0.5 ns 2.1 5.9to2.6

Pogonion⁰ 0.0 ns 3.1 6.0to8.0 0.5 ns 2.8 5.4to4.4

Menton⁰ 0.4 ns 1.9 3.6to3.8 0.6 ns 2.2 4.4to3.4

Angular(8)andlinearmeasurements(mm)

Facialconvexity 1.3 ns 2.9 5.3to4.8 0.3 ns 2.4 3.3to3.9

LstoS-line 1.5 ^** 1.7 4.8to1.1 0.4 ns 1.2 3.3to2.1

LitoS-line 2.3 ^*** 2.0 6.6to0.0 1.4 ^** 1.7 5.2to0.9

T3,24.4daysaftersurgery;T4,2.0yearsaftersurgery;T5,5.5yearsaftersurgery.Negativevaluesimplyabackwardandpositivevaluesaforward movementofthepointinthehorizontalplane.Intheverticalplane,negativevaluesimplyanupwardandpositivevaluesadownwardmovementof thepoint.

* p0.05.

** p0.01.

***p0.001.

Table5. Linearregression.Dependentvariable:pointB⁰(x-value)T5–T3.

Model B 95%confidenceintervalforB

Significance R R²

Lowerbound Upperbound

(Constant) 5.578 1.801 12.956 .125 0.791 0.626

Age .022 .067 .024 .324

IiL/ML⁰atT1 .082 .165 .001 .053

Iiðx-value; T3T2Þ

Asabðx-value; T3T2Þ .015 .051 .020 .358

PointB(x-value)T5–T3 .618 .169 1.066 .011

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studyonfacialgrowthForsberg¹⁹reported thatfromtheageof24to34yearsthenose grewforward, thelipsretruded,andsoft tissue pogonion moved backwards. This agrees with the authors’ findings when comparing their long-term data for 5.5 years withthatfoundearlierat2.0years after surgery.The neteffect ofpointB⁰ and the labrale inferior decreased over time. Another reason for the difference in pointB⁰ andlabraleinferiorcouldbe themissingdatafromthe16patientswho couldnotbere-examinedforthe5.5year follow-up.

5.5 years postoperatively, correlations were found between patient’s age and changes (T5–T3) of differentsoft tissue points. An increase in the patient’s age wassignificantlycorrelatedwithadown- wardmovementoftheverticalory-value ofpogonion⁰(p<0.05)andtoabackward movementofthehorizontalorx-valuesof labrale inferior and pogonion⁰ (both p<0.05). Thus it is possible that soft tissuestrengthwasreducedinthispatient samplebyfurtherageing.

Totheauthors’knowledge,thereisno otherpublisheddataonadultpatientsafter DO of the anterior mandibular alveolar processwhichmakesadirectcomparison ofthedataimpossible.Softtissuechanges compared to skeletal changes were reportedafterDOformandibularelonga- tion in children with hypoplastic mand- ibles evaluated on lateralcephalograms³ or photographs combined with postero- anterior cephalograms.¹ Melugin et al.³ found in27paediatricpatientsthatpoint B⁰ followed point B and pogonion⁰ to pogonion to 90% at post-consolidation.

The magnitudeoftheadvancement, and age,andsexofthepatientshadnoeffect ontheseratios.

In contrast, Joss et al.²⁰systematically reviewed the effectof BSSO withrigid internal fixation (RIF) or wire fixation (WF)formandibularadvancementonsoft tissueratios. Short-and long-termratios forlowerliptolowerincisorinRIForWF can be described as50%. Nodifference between short- and long-term ratios for point B⁰ to point B and pogonion⁰ to pogonion couldbeobserved. Itcouldbe

characterizedasa1to1ratio.Theexcep- tionwasthatpogonion⁰topogonionwith RIFtendedtobehigherthana1to1ratio inlong-termresults.Theupperlipshowed mainlyretrusionbuthighvariability.The ratiosforthelowerlipandpointB⁰found in that review on BSSO for mandibular advancementinRIFandWF²areinaccor- dance with the present authors’ earlier data2.0yearsaftersurgery.Thedatafrom the presentstudyshowthatpointB⁰ fol- lowedpointBnotina1to1ratiobutonly to80%andlabraleinferioronlyto24%.

Theamountofadvancement(T3–T1,x- value)atpointBwassignificantly corre- latedwithanupwardmovementofthey- values oflabrale inferior(p<0.01) and stomion inferior (p<0.05). Joss et al.⁶ could not show anycorrelation between therelapseinsofttissueandtheamountof advancementatpointBintheirlong-term study onhard and soft tissuechange in patients with BSSO for mandibular advancementandRIF.Itisinterestingto notethattheamountandtype(rotational vs. translational) of advancement in the samepatientpopulationexaminedearlier were not correlated with the amount of skeletalrelapsemeasuredatincisioninfer- ior orpointB.^2,14

Animportantshort-termeffectofmax- illofacialsurgeryandaconfoundingvari- able is postoperative swelling (oedema fromretraction,irritations,andinflamma- tion).Forthisreason,theimmediateshort- termsofttissueprofilechangesmeasured on lateral cephalograms always include swellingandthicknessoftheorthodontic brackets.²⁰Furthermore,RIFintheform oftheminiplatesusedinthepresentstudy addsmorevolumetothelabialsurfaceof thechinbonewhichaffectsthesofttissue profileandlimitstheexactlocationofthe cephalometric landmarks. Miniplates werepresentatT2andT3 butsurgically removedbeforeT4inallbutonepatient.

Theremovaloftheminiplatescouldhave ledtoaslightincreaseinsofttissuechange (T4–T3) of point B⁰.¹³ In addition, the interface of the surgical section of the anterioraspectofthesymphysiswasmore susceptibletoresorptionandbonyremo- delling.^2,14

Inconclusion,thislong-termfollow-up of5.5yearsfoundthatfurtherchangein softtissuesoccurredbetween2.0and5.5 years postoperatively regarding pointB⁰ and labrale inferior. The physiological processofageing andloss ofsofttissue elasticityshouldbeconsideredaspossible reasons.

Competinginterest Nonedeclared.

Funding None.

Ethicalapproval

Yes.Ethicalapprovalwasadmittedbythe Ethic Committee of the Kanton Zu¨rich, Switzerland,number593.

Acknowledgements. This article is dedi- cated tothe memory of Dr. Med.Dent.

Michele Antonini who passed away in September 2009. He will always be rememberedforhiscontributiontoortho- dontics.

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Table6. Linearregression.Dependentvariable:labraleinf.(x-value)T5–T3.

Model B 95%confidenceintervalforB

Significance R R²

Lowerbound Upperbound

(Constant) .328 2.098 2.754 .773 0.721 0.520

Age .070 0.148 .008 .075

NL/ML⁰atT1 .013 .717 .742 .971

Incisioninf.(x-value)T5–T3 .049 .573 .671 .866

Incisionsup.(x-value)T5–T3 .599 .098 1.296 .086

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Address:

DepartmentofOrthodonticsand CraniofacialBiology

RadboudUniversityNijmegenMedical Centre

Nijmegen TheNetherlands Tel.:+31243614005

E-mail:christofjoss@hotmail.com Softtissuestabilityafterdistractionosteogenesis