ORIGINAL ARTICLE

Three-dimensional soft-tissue and hard-tissuechanges in the treatment of bimaxillaryprotrusion

R. Christian Solem,a RichardMarasco,b Luis Guiterrez-Pulido,b Ib Nielsen,c Seong-Hun Kim,d andGerald Nelsone

San Francisco, Calif, and Seoul, Korea

aOrthScienbDentcProfeUnivedProfeUniveeProfeScienAll auPotenReprinDivisiSan FSubm0889-Copyrhttp:/

218

Introduction: Facial convexity related to bimaxillary protrusion is prevalent in many populations.Underlying skeletal protrusion combined with increased dentoalveolar protrusion contributes to facial muscleimbalance and lip incompetence, which is undesirable for many patients. In this study, we evaluated therelationship between soft-tissue and hard-tissue changes in an orthodontically treated Asian population.Methods: Twenty-four consecutive adult Asian patients (mean age, 24 years), diagnosed with severebimaxillary dentoalveolar protrusion, were evaluated using pretreatment and posttreatment cone-beamcomputed tomography. The patients were treated with 4 first premolar extractions followed by anteriorretraction with either skeletal or intraoral anchorage. Serial cone-beam computed tomography radiographswere registered on the entire cranial base and fossa. Soft-tissue and hard-tissue changes were determinedthrough landmark displacement and color mapping. Results: Upper lip retraction was concentrated betweenthe nasolabial folds and commissures. Lower lip retraction was accompanied by significant redistribution ofsoft tissues at pogonion. Soft-tissue changes correlated well with regional facial muscle activity. Significantretractions (2-4 mm) of the soft tissues occurred beyond the midsagittal region. Use of skeletal anchorageresulted in 1.5 mm greater lower lip retraction than intraoral anchorage, with greater retraction of the maxillaryand mandibular incisor root apices. Conclusions: Profound soft-tissue changes accompanied retraction ofthe anterior dentition with both treatment modalities. (Am J Orthod Dentofacial Orthop 2013;144:218-28)

Bimaxillary protrusion is a common dentofacialtrait particularly prevalent in Asian and Africanpopulations and present in almost every ethnic

group.1-6 Underlying skeletal prognathism anddentoalveolar protrusion produce a convex lower facialprofile, procumbent lips, and a protrusive anteriordentition, often resulting in lip incompetence, mentalisstrain, and excessive gingival display. This situation is

odontic resident, Division of Orthodontics, Department of Orofacialces, University of California, San Francisco.al student, School of Dentistry, University of California, San Francisco.ssor emeritus, Division of Orthodontics, Department of Orofacial Sciences,rsity of California, San Francisco.ssor, Department of Orthodontics, School of Dentistry, Kyung Heersity, Seoul, Korea.ssor and acting chair, Division of Orthodontics, Department of Orofacialces, University of California, San Francisco.thors have completed and submitted the ICMJE Form for Disclosure oftial Conflicts of Interest and none were reported.t requests to: R. Christian Solem, Department of Orofacial Sciences,on of Orthodontics, University of California, 707 Parnassus Ave,rancisco, CA 94143; e-mail, Richard.Solem@ucsf.edu.itted, November 2012; revised and accepted, March 2013.5406/$36.00ight � 2013 by the American Association of Orthodontists./dx.doi.org/10.1016/j.ajodo.2013.03.018

esthetically unacceptable to some patients, and theyseek treatment by an orthodontist or oral surgeon.Both orthodontic and surgical treatments can improvefacial balance. Orthodontic treatment can correctdentoalveolar protrusion by uprighting and retractingthe anterior teeth, typically after the extraction of 4premolars. Surgical treatment reduces protrusion byrepositioning segments of the jaws. Both treatmentapproaches can reduce facial convexity and improve lipposture significantly.

Improvement of the soft-tissue profile depends onmany variables related to the anatomy of the face,including lip thickness, facial muscle activity, andethnicity.7-12 The relationship between dentoalveolarmovement and soft-tissue change is complex andcontingent on soft-tissue relationships in all 3 planesof space.13-21 Previous studies have focused on lipchanges only in the midsagittal plane, usingsuperimposed lateral cephalograms and facial photos.6

However, the 2-dimensional approach fails to considerthe complex 3-dimensional (3D) geometry of the humanface.13,22 In particular, soft-tissue changes in the frontalview are judged more severely by patients but are often

Fig 1. A, Initial cephalometric measurements were madeusing a section centered at the midsagittal plane andaligned to the Frankfort horizontal plane. Dentoalveolarprotrusion was quantified bymeasuring the horizontal dis-tance from the most anterior point on the maxillary andmandibular incisors to the hard tissue A-point–pogonionline. Lip thickness was measured from the most anteriorpoints on the upper and lower lips to the cervical aspectsof the maxillary and mandibular incisors, respectively.B, Changes to the lips between pretreatment andposttreatment were measured by dividing the intercom-missure distance into 5 sagittal planes and placinglandmarks at the most anterior point on the upper andlower lips in each plane.

Solem et al 219

overlooked in clinical studies.23 Computer simulationsthat predict soft-tissue changes from orthodontic andsurgical movement rely on relationships derived fromthe midsagittal plane. Accurate treatment predictionsrequire data on the 3D relationships between hard-tissue and soft-tissue changes. Advances in 3D imagingwith cone-beam computed tomography (CBCT) and 3Dphotography can be used for global evaluation of thesechanges.13,14,22,24-27

This study was designed to evaluate the 3D changesin soft tissues resulting from hard-tissue changesproduced by orthodontic treatment of bimaxillaryprotrusion. The goals were to (1) characterize the 3Dchanges to the face and skeleton resulting fromretraction of the anterior teeth, (2) identify and quantifyrelationships between incisor and lip movement outsidethe midsagittal plane, and (3) test differences in resultsusing skeletal and nonskeletal anchorage mechanics inthe treatment of bimaxillary protrusion.

MATERIAL AND METHODS

The study population consisted of 24 consecutivenongrowing Asian patients with bimaxillary dentoalveo-lar protrusion treated in the orthodontic clinic at theUniversity of California, San Francisco. All were treatedwith extraction of 4 first premolars and retraction ofthe anterior dentition using controlled maxillaryanchorage. Institutional review board approval for thestudy was obtained from the University of Californiabefore treatment.

The inclusion criteria for the patients were Class Imolar and canine relationships, mild or no crowding,severe dentoalveolar protrusion, and complete pretreat-ment and posttreatment CBCT radiographs and photos.Only Asian adults were included. The group was mostlyfemale (n5 20), with ages ranging from 20 to 29 years.Initial protrusion was quantified by measuring thedistance between the most anterior point on the maxil-lary and mandibular incisors to the A-point–pogonionalong a line parallel to the Frankfort horizontal (Fig 1,A). Lip thickness was measured from the cervical aspectof the maxillary and mandibular incisors to the mostanterior point on the upper and lower lips (labralesuperius and labrale inferius), respectively (Fig 1, A).All patients had greater than 2 SD of protrusion of themaxillary and mandibular incisors relative to Asianmeans (Table I). The degrees of maxillary and mandibu-lar incisor protrusion, skeletal protrusion (defined bySNA and SNB angles), sagittal jaw relationship(defined by ANB angle), lip thickness, and maxillaryand mandibular crowding were similar between thetreatment groups (Table I). The differences were notstatistically significant (P .0.05).

American Journal of Orthodontics and Dentofacial Orthoped

Patients meeting the inclusion criteria were dividedinto 2 treatment groups based on the type of anchorageused. Both groups were treated with extraction of 4 firstpremolars and full fixed appliances with an 0.018-in slotand twin brackets (3M Unitek, Monrovia, Calif; orEnsignia; Ormco, Orange, Calif). After the resolution ofanterior crowding, the mandibular anterior teeth wereretracted en masse in both groups as shown (Fig 2). Inthe skeletal anchorage group (n 5 11), bilateral C-tubetemporary skeletal anchorage miniplates28 wereplaced mesially to the maxillary first molar (Fig 2). Themaxillary anterior teeth were then retracted en masseon a 0.016 3 0.022-in stainless steel archwire usingelastomeric chain ligated from the C-tube to a canineretraction arm placed close to the height of the centerof resistance. In the nonskeletal anchorage group(n 5 13), the maxillary canines were first retractedsegmentally on a 0.016 3 0.022-in stainless steelarchwire using a soldered 0.032-instainless steel trans-palatal archbar or arch between the maxillary first molarsfor anchorage (Fig 2). After retraction of the canines, themaxillary incisors were retracted en masse usingintrusion-retraction loops placed distally to the lateral

ics August 2013 � Vol 144 � Issue 2

Table I. Population characteristics

Nonskeletalanchoragemean (SD)

Skeletalanchoragemean (SD)

Pvalue

U1i-A Pg (mm) 10.67 (2.38) 11.58 (2.57) 0.68L1i-A Pg (mm) 6.43 (3.19) 6.81 (3.26) 0.91SN/MP (�) 34.02 (5.84) 36.22 (5.64) 0.40U1/PP (�) 122.10 (6.70) 119.58 (5.74) 0.45L1/MP (�) 99.40 (5.35) 98.23 (4.98) 0.62SNA (�) 83.79 (3.81) 83.29 (4.10) 0.45SNB (�) 80.35 (4.42) 80.34 (3.45) 0.91Maxillary crowding (mm) �3.90 (2.02) �3.85 (0.84) 0.94Mandibular crowding (mm) �2.60 (0.75) �2.85 (0.57) 0.99UL thickness (mm) 11.59 (1.45) 10.65 (2.59) 0.33LL thickness (mm) 12.62 (1.64) 12.88 (2.08) 0.71Age (y) 21.6 (7.1) 27.4 (7.9) 0.10Sex (% female) 91 70 0.22

U1i, Maxillary incisal edge; A Pg, hard-tissue A-point to pogonionline; L1i, mandibular incisal edge; U1, maxillary central incisor;MP, mandibular plane; PP, palatal plane;UL, upper lip; LL, lower lip.

220 Solem et al

incisors. Finishing was performed on a 0.0175-in squarestainless steel archwire.

CBCT scans were taken at pretreatment andposttreatment using a CB MercuRay machine (Hitachi,Tokyo, Japan). Both scans were taken with the patientin maximum intercuspation with the lips and face in re-pose, as instructed by the technician. A scan captured512 images with a 12-in diameter spherical volume en-compassing the face, jaws, and entire cranial base. Thevoxel dimension was 0.376 mm3. DICOM data setswere converted into Amira mesh files (Visage Imaging,San Diego, Calif) and manipulated with the Amira soft-ware (version 5.4.2, Visage Imaging).

The pretreatment and posttreatment scans wereregistered on stable structures in the cranial base.Regions of the scan volumes were individually defined asa reference, masking structures outside the volume. Thisregion included the entire cranial base, zygomatic arches,maxillary sinuses, frontal bone, and posterior cranial fossa(Fig 3). These structures are stable in nongrowingpatients.29-32 The masked posttreatment volume wasthen reoriented via isometric rigid translation androtation onto the cranial base of the pretreatment scanusing an automated, voxel-based algorithm thatmaximizes mutual information between the volumes.25,27

After the volumes were registered on the cranial base,the hard-tissue skeleton and exterior soft-tissue surfacewere isolated using voxel-value based segmentation.The segmentation values were selected for optimalrendering and kept constant for all time points andpatients. Triangular mesh surfaces were then generatedrepresenting the skeleton, teeth, and exterior facialsoft tissues. To quantify the relative changes between

August 2013 � Vol 144 � Issue 2 American

the pretreatment and posttreatment surfaces, vectorswere calculated from each vertex on the pretreatmentsurface to the nearest point on the posttreatmentsurface, with a length equal to the Euclidean distancebetween the points. To determine the degree of changerelative to the surface, the component of the vectorperpendicular to the pretreatment surface was calcu-lated, representing either outward (positive) or inward(negative) displacement of the surface. Surface distanceswere converted into a color scale, with longerwavelength colors (red) representing inward displace-ment, and shorter wavelength colors (blue) representingoutward displacement (Fig 3). Green indicated nodisplacement. The color maps are a global approxima-tion of actual surface displacements.

The accuracy of the cranial base registration wasverified by visualizing the surface displacement map ofthe interior surface of the cranial fossa. The onlydeviation occurred at the boundary of the scans, whichare not identical because of differences in patientorientation. Based on the color scale, differences betweenthe surfaces was less than 0.5 mm over the region of thecranial fossa. CBCT registrations were repeated by 2 inde-pendent observers (R.C.S. and R.M.) to verify consistency.Two-dimensional slices were taken through the maxillaryand ethmoid sinuses to confirm the superimposition ofthe trabeculae and finer structures in the sinus.

To quantify absolute changes to the dentition andsoft tissues, landmark points were defined on the teethand lips with InVivo software (InvivoDental5.0;Anatomage, San Jose, Calif). A coordinate system wasconstructed using an adjusted Frankfort horizontalplane passing through sella prime, right porion, andright orbitale. Orthogonal vertical planes passingthrough nasion were defined relative to the horizontal.Twelve hard-tissue landmarks were selected on the seg-mented surfaces of the skull and teeth. These landmarksincluded the right and left maxillary and mandibularcentral incisor edges and root apices, and the maxillaryand mandibular first molar crowns and mesiobuccalroot apices. Ten soft-tissue landmarks were definedby dividing the lips into 5 equally spaced slices span-ning the intercommissure length (Fig 1, B). The mostanterior points on the upper and lower lips were land-marked in each sagittal section (Fig 1, B). Vectors werethen determined at each landmark between thepretreatment and posttreatment surfaces, representingmovement at each location between time points.A separate mandibular superimposition using establi-shed stable structures was performed to measure themovement of the mandibular incisors.31

Digital 2-dimensional cephalometric tracings weregenerated and superimposed on the cranial base by

Journal of Orthodontics and Dentofacial Orthopedics

Fig 2. Clinical photos of the space-closing mechanics used in the 2 treatment groups. The mandibulararch was treated the same in both groups. After alignment and resolution of crowding, the mandibularanterior dentition from canine to canine was retracted en masse on 0.016 3 0.022-in stainless steelwire in 0.018-in slot brackets using elastomeric chains ligated from the first molar to the canine. Inthe skeletal anchorage group, the maxillary anterior dentition was retracted en masse with a 0.0163 0.022-in stainless steel archwire passing through the labial c-tube temporary skeletal anchorageminiplates placed mesially to the maxillary first molar. Elastomeric chains were ligated from hookson the archwire to the C-tube for retraction. In the nonskeletal anchorage group, the maxillary canineswere retracted segmentally on a 0.0163 0.022-in stainless steel archwire using a transpalatal archbaror arch between the maxillary first molars for anchorage.

Solem et al 221

using TIOPS software (Roskilde, Denmark; www.tiops.com). Lateral cephalograms were generated from theCBCT data with Dolphin software (version 11.7; DolphinImaging, Chatsworth, Calif).

Statistical analysis

Displacement vectors for landmarks on the centralincisors and lips were determined between pretreatmentand posttreatment on the CBCT radiographs. The

American Journal of Orthodontics and Dentofacial Orthoped

inclination changes of the incisors were measured asthe change in axial inclination between pretreatmentand posttreatment. The vertical and anteroposteriorcomponents of each vector were averaged betweenthe right and left incisors. The anteroposterior compo-nents of lip movement were averaged across 5 planesspanning the intercommissure length for the upperand lower lips to determine the average anteroposteriormovement for each lip.

ics August 2013 � Vol 144 � Issue 2

Fig 3. Registration method for the pretreatment and posttreatment CBCT scans. Hard tissue wassegmented, and the cranial fossawas separated from the skull. The scanswere registered using a rigid,automated, voxel-wise registration algorithm maximizing mutual information. Surface discrepanciesbetween registered hard-tissue surfaces at both times are shown at 0.5 mm resolution. Green, No dif-ference; blue, �0.5 mm difference; red, 10.5 mm difference.

222 Solem et al

The validity of superimposition and landmarkplacement was determined by having 2 independentobservers (R.C.S. and R.M.) perform multiple observa-tions on the records of 10 randomly selected patientsfrom the combined groups. These calibrated observersrepeated superimposition and landmark placement at2-week intervals to determine interobserver and intraob-server errors. The variability in the anteroposterior andvertical components of the displacement vectors be-tween observations was used to calculate intraclass cor-relation coefficients to test reliability. These values forintraobserver and interobserver correlations were allgreater than 0.85. In addition, Bland-Altman plots33

were made to analyze the interobserver differences.Histograms were constructed for all variables to assessnormality. Because of the small sample size and thelack of normality, nonparametric methods were used.Intergroup differences were compared using theWilcoxon rank sum test. Interactions between variableswere mostly linear, as determined from testing in linearand quadratic models. The nonparametric Spearmanrank correlation coefficient was calculated for eachcomparison and adjusted for multiple comparisons us-ing the Holm-Sidak correction. The Stata software

August 2013 � Vol 144 � Issue 2 American

package (StataCorp, College Station, Tex) was used forstatistical calculations.

RESULTS

The profiles of our patients were characterized byconvexity of the lower facial third. The typical lip profilewas protrusive, demonstrating either mentalis strain oran interlabial gap at rest. The variability in lip thicknesswas relatively low in the population (mean SD of 1.94mm). Crowding was mild (\4 mm) in each arch andnot significantly different between groups (Table I).The skeletal sagittal jaw relationship was within normallimits in both groups. There were no statisticallysignificant (P.0.05) differences in the dental or skeletalparameters between the groups.

The maxillary incisor edges were retracted 1.47 mmmore posteriorly on average in the skeletal anchoragegroup than in the nonskeletal group (P 5 0.13;Table II). The root apices of the maxillary incisors inthe skeletal anchorage group were retracted approxi-mately 0.9 mm on average, with little apical rootretraction in the nonskeletal anchorage group(P 5 0.053; Table II). This movement was accompaniedby 3.36� of greater reduction on average in maxillary

Journal of Orthodontics and Dentofacial Orthopedics

Table II. Intergroup differences

Mean movement (pretreatment-posttreatment)

Nonskeletal anchorage Skeletal anchorage

Difference P valueMean (SD) Mean (SD)UL retraction (mm) 2.26 (0.33) 2.67 (0.36) �0.49 NSLL retraction (mm) 2.63 (0.40) 4.12 (0.73) �1.49 0.051U1i retraction (mm) 4.16 (0.74) 5.63 (0.66) �1.47 0.13U1i extrusion (mm) 1.79 (0.37) 1.84 (0.37) �0.04 NSU1 root retraction (mm) �0.081 (0.33) 0.89 (0.47) �0.97 0.053L1i retraction (mm) 3.39 (0.74) 3.14 (0.71) �0.25 NSL1i intrusion (mm) 0.40 (0.23) 0.54 (0.37) �0.13 NSU1 retroclination (�) 13.18 (2.60) 9.82 (1.59) �3.36 NSL1 retroclination (�) 8.75 (1.45) 9.89 (1.72) �1.14 NSU6 crown A-P (mm) 1.95 (0.40) �0.45 (0.55) 2.40 0.008*U6 root A-P (mm) 1.81 (0.33) �0.53 (0.32) 2.34 0.0004*U6 crown extrusion (mm) 0.02 (0.23) 0.83 (0.46) �0.81 0.17

Lip retraction was measured as the mean anteroposterior retraction at 5 landmarks spanning the intercommissure distance.UL, Upper lip; LL, lower lip; U1i, maxillary incisal edge; U1, maxillary central incisor; L1i, mandibular incisal edge; L1, mandibular central incisor;U6, maxillary first molar; A-P, anteroposterior.*P\0.05; NS indicates P .0.2.

Solem et al 223

incisor proclination in the nonskeletal anchorage group.These differences, however, were not statisticallysignificant with the available sample size. Movementof the maxillary incisor edge followed a consistentinferior and posterior vector, with a high degree ofcorrelation between anteroposterior and vertical move-ment (P 5 0.0005; Table III). The sagittal and verticalmovements of the maxillary incisors were highly corre-lated with the degrees of retroclination (P 5 0.0002;Table III), indicating primarily an apex-centered tippingmovement, especially in the nonskeletal anchoragegroup.

The reduction in mandibular incisor proclinationwas not significantly different between treatmentgroups. Movement of the mandibular incisors wasmore variable in both groups. Coordination bet-ween vertical and horizontal movement was low(r 5 �0.10; Table III), indicating significant variabilityin the vector of movement. Retraction of the anteriorteeth was accompanied by significant remodeling ofthe supporting alveolar bone. In both groups, remodel-ing of alveolar bone was measured around the roots ofthe maxillary and mandibular anterior teeth, and it wasapproximately 1 to 2 mm in magnitude (Figs 4,A2-C2, and 5, A2-C2).

The maxillary first molars moved significantly moremesially (2.40 mm) in the nonskeletal anchorage group(P 5 0.008; Table II). No significant difference was de-tected in the vertical movement of the maxillary molars.However, there was considerable variability in verticalmovements between subjects. This vertical movementproduced measurable degrees of forward (Fig 4, A1) orbackward (Fig 5, C1) rotation of the mandible.

American Journal of Orthodontics and Dentofacial Orthoped

Three-dimensional soft-tissue displacement variedconsiderably between patients and treatment groups(Figs 4, A3-C3, and 5, A3-C3). Significant redistribu-tions of soft tissues were measured at the submentalsulcus and soft-tissue pogonion. The lip changeextended to the nasolabial folds laterally, the columellasuperiorly, and the mentolabial sulcus inferiorly. Pa-tients beginning with a resting interlabial gap showedthe greatest change in lower lip position in response tomaxillary incisor retraction (Figs 4, A3 and C3, and 5,C3). Changes outside the lip region were seen in thelateral views in several patients, notably in themasseter region and cheeks, where inward soft-tissuemovements were detected (Figs 4, C3, and 5, C3).Some patients experienced significant changes inweight during the treatment period, as noted in theirfacial photographs, consistent with generalizedretraction of soft tissues in the cheeks. In patients inwhom the mandibular plane angle decreased due tomaxillary molar intrusion, the chin moved anteriorly,as shown in the skeletal and soft-tissue projections(Fig 4, A1 and A3).

Mean lower lip retraction was greater in the skeletalanchorage group by 1.49 mm, but this was notstatistically significant (P 5 0.051; Table II). Retractionof the lower lip was significantly correlated with theanteroposterior movements of the mandibular incisors(r 5 0.71; Table III), with little correlation (r 5 0.52;Table III) with upper incisor anteroposterior movement.Retraction of the upper lip was highly correlated withanteroposterior movement of the maxillary incisors(r 5 0.74; Table III) and slightly correlated withanteroposterior movement of the mandibular incisors

ics August 2013 � Vol 144 � Issue 2

Table III. Soft-tissue and hard-tissue variable correlations both groups combined

UL ret LL ret U1i y U1i z U1 retro L1 retro L1i y L1i zUL ret – 0.69 0.74* �0.60 0.53 0.26 0.63 �0.27LL ret 0.08 – 0.52 �0.24 0.26 0.30 0.71* �0.14U1i y 0.02* 0.50 – �0.81* 0.83* 0.25 0.51 �0.36U1i z 0.16 NS 0.0005* – �0.89* �0.05 �0.30 0.44U1 retro NS NS 0.0002* \0.0001* – 0.13 0.25 �0.36L1 retro NS NS NS NS NS – 0.23 �0.14L1i y 0.10 0.016* NS NS NS NS – �0.10L1i z NS NS NS NS NS NS NS –

Both groups combined (n5 24). Spearman rank correlation coefficients (r) are in the upper right half of the table; significance levels are in the lowerleft half.UL ret and LL ret, Mean anteroposterior retraction of the upper and lower lips, respectively; U1i, maxillary incisal edge; y, anteroposterior incisaledge movement; z, vertical incisal edge movement; U1, maxillary central incisor; retro, retroclination; L1, mandibular central incisor; L1i,mandibular incisal edge.*P\0.05; NS indicates P .0.5.

224 Solem et al

(r5 0.63; Table III). Correlation with vertical movementof the maxillary incisors was observed, but it was notstatistically significant (r5�0.60; Table III). Significantlip retraction occurred in vertical sections away from themidline, diminishing only slightly toward the nasolabialfold (Figs 4, A3-C3, and 5, A3-C3). The retractionvector progressed from an anteroposterior direction atthe midsagittal plane to a more laterally orientedvector near the commissures. The lower lip retractionzone was narrower, bounded by the submentalsulcus inferiorly and the commissures laterally(Figs 4, A3-C3, and 5, A3-C3).

DISCUSSION

Interpretation of the true soft-tissue displacement iscomplicated by confounders such as weight change,variations in head posture, and facial muscle activ-ity.9,34 We observed significant retraction of the upperand lower lips during treatment; this correspondedwith values from previous studies.5,6,21,35-38 There wasconsiderable individual variability in lip retraction.Three-dimensional studies of soft-tissue changes aftersurgical midface LeFort I advancement showed similarpatterns of change, bounded by the nose mediallyand the nasolabial fold laterally.13 The soft-tissuechange after surgical advancement of the maxillaryalveolar process was concentrated in a triangular areaspanning the nasolabial folds, similar to our measure-ments.13

The shape of the nasolabial fold is specifically influ-enced by muscle activity and age, and the nasolabial folddisappears in a paralyzed face.39 It is made up of densefibrous tissue and striated muscle bundles, with inser-tions for the levator muscles of the upper lip. This con-nective tissue plane might function as a boundary toupper lip retraction, accompanied by changes in resting

August 2013 � Vol 144 � Issue 2 American

muscle activity in the lip levator and orbicularis oris mus-culature. Other studies have noted significant changes atthe soft-tissue pogonion level from orthodontic retrac-tion or anterior segmental osteotomy.40 These changesmight be related to relaxation of the mentalis muscleand redistribution of the soft tissues in response to den-tal retraction.40 Three-dimensional evaluation of lowerlip changes after surgical mandibular setback followeda similar pattern, with changes concentrated over thecentral portions of the lower lip and chin.22 Orthodonticretraction in this study produced lower lip changes thatdiminished toward the commissures in proportion to thedegree of retraction. However, in patients with signifi-cant lower lip eversion, the extent and zone of retractionwas significantly greater, extending beyond the commis-sures to the buccal regions.

The relationship between lip retraction and anteriorincisor movement relies on complex multifactorial rela-tionships that depend on lip strain and thickness,12 den-tofacial morphology,21 and ethnicity and sex.5,6,16,41

Soft-tissue changes can be predicted using linearapproximations of these relationships. Studies of lipmovement after retraction of anterior teeth in Japanesepopulations showed that upper lip retraction correlatedstrongest with horizontal retraction of the maxillaryincisor, followed by vertical movement of the mandibu-lar incisor.6,35 Our measurements yielded similar results,indicating a strong correlation of upper lip retractionwith maxillary incisor anteroposterior retraction. Inaddition, we observed that upper lip retraction slightlycorrelated with mandibular incisor anteroposteriorretraction and maxillary incisor vertical movement,consistent with the results of previous studies.5,6,38

These studies also showed a strong correlationbetween lower lip retraction and both maxillaryand mandibular incisor anteroposterior retraction.

Journal of Orthodontics and Dentofacial Orthopedics

Fig 4. Two-dimensional cephalometric tracings (A1-C1), 3D hard-tissue (A2-C2), and soft-tissue(A3-C3) superimpositions of 3 patients (A-C) representing variations in the skeletal anchorage group.Two-dimensional tracings are superimposed on the cranial base. Black, Pretreatment; red, posttreat-ment. Hard-tissue and soft-tissue colored displacement maps are projected onto the pretreatmentCBCT scan. Color scale ranges from�2 mm (red, subtractive change) indicating inward displacement,to 12 mm (blue, additive change) indicating outward displacement; green, no change.

Solem et al 225

In contrast, our subjects showed lower lip retractionstrongly correlated only with anteroposterior retractionof the mandibular incisors. Brock et al38 showed a strongcorrelation of upper lip movement with displacement oflandmarks on the facial and cervical aspects of themaxillary incisor, consistent with our observations.

American Journal of Orthodontics and Dentofacial Orthoped

The ratio of maxillary incisor retraction to the meanupper lip retraction was 1.73:1 (Table IV); this is midwaybetween reported ratios from 1.5:142 to 2.5:137 inbimaxillary dentoalveolar protrusive Asian popula-tions.5,6,35,37,40-42 The ratio of mandibular incisorretraction to mean lower lip retraction in this study was

ics August 2013 � Vol 144 � Issue 2

Fig 5. Two-dimensional cephalometric tracings (A1-C1), 3Dhard-tissue (A2-C2), andsoft-tissue (A3-C3)superimpositions of 3 patients representing variations in the nonskeletal anchorage group. Hard-tissueand soft-tissue colored displacement maps are projected onto the pretreatment CBCT scan. Color scaleranges from �2 mm (red, subtractive change) indicating inward displacement, to12 mm (blue, additivechange) indicating outward displacement; green, no change.

226 Solem et al

0.83:1 (Table IV), correspondingly lower than the ratios of1.1242 to 1.32:135 reported in previous studies. However,these correlation coefficients considered only the antero-posterior component of incisormovement, when both themaxillary and mandibular incisors are also moving verti-cally. Significant intrusion and reduction of overbite

August 2013 � Vol 144 � Issue 2 American

weremeasured in both groups in this study; these changesalso contributed to anteroposterior lip retraction. Upperlip retraction was more sensitive to vertical incisor move-ment than was anteroposterior movement, with a ratio of�0.61 maxillary incisor vertical movement to upper lipanteroposterior retraction.Measurements of lip retraction

Journal of Orthodontics and Dentofacial Orthopedics

Table IV. Soft-tissue and hard-tissue variable interactions: linear regression slopes both groups combined

UL ret LL ret U1i y U1i z U1 retro L1 retro L1i y L1i zUL ret – 0.69 0.74* �0.60 0.53 0.26 0.63 �0.27LL ret 1.18 (0.51 to 1.84) – 0.52 �0.24 0.26 0.30 0.71* �0.14U1i y 1.73* (1.07 to 2.40) 0.71 (0.22-1.20) – �0.81* 0.83* 0.25 0.51 �0.36U1i z �0.61 (�0.98 to �0.24) NS �0.35* (�0.51 to �0.19) – �0.89* �0.05 �0.30 0.44U1 retro 4.00 (1.27 to 6.71)�/mm NS 2.72* (1.76-3.68)�/mm �6.35*

(�7.86 to �4.84)�/mm– 0.13 0.25 �0.36

L1 retro NS NS NS NS NS – 0.23 �0.14L1i y 1.07 (�1.84 to �0.29) 0.83* (0.45-1.22) 0.56 (0.19-0.93) NS NS NS – �0.10L1i z NS NS NS 0.84 (0.17-1.52) NS NS NS –

Values of the slope of linear regression. Spearman rank correlation coefficients (r) are in the upper right half of the table; linear regression slopes arein the lower left half. Dependent variables are indicated in the left column heading; independent variables are indicated in the upper row heading.Values in parentheses are the 95% confidence intervals.UL ret and LL ret, Mean anteroposterior retraction of the upper and lower lips, respectively; U1i, maxillary incisal edge; y, anteroposterior incisaledge movement, with posterior being positive; z, vertical incisal edge movement, with superior being positive; U1, maxillary central incisor; retro,retroclination; L1, mandibular central incisor; L1i, mandibular incisal edge.*P\0.05; NS indicates P .0.5.

Solem et al 227

lateral to the midline were also greater in many subjects,contributing to a greater average lip retraction thanseen with conventional 2-dimensional measurements. Asimilar effect was observed in 3D midfacial soft-tissuechanges resulting from surgical mandibular setback,with greater retraction away from the midline.22

The difference could also be related to severe pre-treatment lip strain in this group. Many patients in thisstudy exhibited a resting interlabial gap or an evertedlower lip in repose, indicating high lip strain when thelips are closed. Previous studies demonstrated greaterlip sensitivity in patients with either high lip strain orthin lips.9,12 Patients with a large resting interlabialgap showed the greatest lip retraction response permillimeter of incisor retraction. Retraction of theincisors in our study might have induced changes in lipposture and facial muscle balance that could haveamplified lip changes, resulting in lower ratios ofincisor to lip retraction. One could conclude that thelip response after treatment follows a nonlinearrelationship with respect to initial lip protrusion.

The difference in lower lip retraction betweenanchorage types was consistent with results fromprevious studies showing significantly greater lower lip re-traction in the skeletal anchoragegroup,withnodetectabledifference in upper lip retraction.36 However, this differ-ence represents only 35%of the total anteroposterior lowerlip retraction, which is not likely to be clinically significant.In contrast, studies in a dentally protrusive Chinese popu-lation showed the reverse, with greater upper lip retractionand no significant difference in the lower lip retraction.43

The intergroup difference in retraction of the maxillary in-cisor edges was measurable (1.47 mm) but not statisticallysignificant with the available sample size. Similarly, Liuet al43 reported a 2.27-mm difference in maxillary incisor

American Journal of Orthodontics and Dentofacial Orthoped

retraction in a similar study comparing anchorage typesin a bimaxillary protrusive Asian population. The inter-group difference in maxillary molar anchorage loss in ourstudy (2.4 mm) was less than the observed values in otherstudies (3.3-4.0 mm).36,43 This difference could be relatedto variations in the type of nonskeletal anchorage used inthe treatments; previous studies used either transpalatalarches43 or transpalatal bars,36 occasionally including sec-ond molar ligation and headgear.

CONCLUSIONS

1. Three-dimensional soft-tissue changes resultingfrom retraction of the anterior teeth in patientswith bimaxillary protrusion are variable butcorrelated with initial resting lip posture. Upper lipretraction is concentrated between the nasolabialfolds and commissures laterally. Lower lip retractionis concentrated at the midline, diminishing towardthe commissures. Significant redistribution of thesoft tissues near pogonion can occur.

2. Anteroposterior and transverse lip retraction iscorrelated with both anteroposterior and verticalmovement of the maxillary and mandibular incisors.

3. Clinical soft-tissue changes in bimaxillary protrusivepatients treated with first premolar extractionsare similar with either skeletal or nonskeletal formsof anchorage. Treatment with maxillary skeletalanchorage results in 2.4 mm less maxillary molaranchorage loss.

ACKNOWLEDGMENTS

We thank Earl Johnson and Arthur Miller for helpwith the editing and preparation of this manuscriptand John Huang for helpful analysis ideas.

ics August 2013 � Vol 144 � Issue 2

228 Solem et al

REFERENCES

1. Rosa RA, Arvystas MG. An epidemiologic survey of malocclusionsamong American Negroes and American Hispanics. Am J Orthod1978;73:258-73.

2. Scott SH, Johnston LE Jr. The perceived impact of extraction andnonextraction treatments on matched samples of African Ameri-can patients. Am J Orthod Dentofacial Orthop 1999;116:352-60.

3. Farrow AL, Zarrinnia K, Azizi K. Bimaxillary protrusion in blackAmericans—an esthetic evaluation and the treatment consider-ations. Am J Orthod Dentofacial Orthop 1993;104:240-50.

4. Lamberton CM, Reichart PA, Triratananimit P. Bimaxillaryprotrusion as a pathologic problem in the Thai. Am J Orthod1980;77:320-9.

5. Lew K. Profile changes following orthodontic treatment ofbimaxillary protrusion in adults with the Begg appliance.Eur J Orthod 1989;11:375-81.

6. Hayashida H, Ioi H, Nakata S, Takahashi I, Counts AL. Effects ofretraction of anterior teeth and initial soft tissue variables on lipchanges in Japanese adults. Eur J Orthod 2011;33:419-26.

7. Holdaway RA. A soft-tissue cephalometric analysis and its use in or-thodontic treatment planning. Part II. AmJOrthod1984;85:279-93.

8. Kusnoto J, Kusnoto H. The effect of anterior tooth retraction on lipposition of orthodontically treated adult Indonesians. Am J OrthodDentofacial Orthop 2001;120:304-7.

9. Burstone CJ. Lip posture and its significance in treatmentplanning. Am J Orthod 1967;53:262-84.

10. Kasai K. Soft tissue adaptability to hard tissues in facial profiles.Am J Orthod Dentofacial Orthop 1998;113:674-84.

11. Subtelny JD, Sakuda M. Muscle function, oral malformation, andgrowth changes. Am J Orthod 1966;52:495-517.

12. Oliver BM. The influence of lip thickness and strain on upper lipresponse to incisor retraction. Am J Orthod 1982;82:141-9.

13. KimYI, Kim JR, Park SB. Three-dimensional analysis ofmidfacial softtissue changes according to maxillary superior movement after hor-izontal osteotomyof themaxilla. J Craniofac Surg2010;21:1587-90.

14. Park SB, Kim YI, Hwang DS, Lee JY. Midfacial soft-tissue changesafter mandibular setback surgery with or without paranasalaugmentation: cone-beam computed tomography (CBCT) volumesuperimposition. J Craniomaxillofac Surg 2013;41:119-23.

15. Satravaha S, Schlegel KD. The significance of the integumentaryprofile. Am J Orthod Dentofacial Orthop 1987;92:422-6.

16. HersheyHG. Incisor tooth retraction and subsequent profile changein postadolescent female patients. Am J Orthod 1972;61:45-54.

17. Angelle PL. A cephalometric study of the soft tissue changesduring and after orthodontic treatment. Trans Eur Orthod Soc1973;267-80.

18. Wisth PJ. Integumental profile changes caused by surgicaltreatment of mandibular protrusion. Int J Oral Surg 1975;4:32-9.

19. Wisth J. Soft tissue response to upper incisor retraction in boys. BrJ Orthod 1974;1:199-204.

20. Rains MD, Nanda R. Soft-tissue changes associated with maxillaryincisor retraction. Am J Orthod 1982;81:481-8.

21. Talass MF, Talass L, Baker RC. Soft-tissue profile changes resultingfrom retraction of maxillary incisors. Am J Orthod DentofacialOrthop 1987;91:385-94.

22. Kim M, Lee DY, Lim YK, Baek SH. Three-dimensional evaluation ofsoft tissue changes after mandibular setback surgery in Class IIImalocclusion patients according to extent of mandibular setback,vertical skeletal pattern, and genioplasty. Oral Surg Oral Med OralPathol Oral Radiol Endod 2010;109:e20-32.

23. Gosain AK, Amarante MT, Hyde JS, Yousif NJ. A dynamic analysisof changes in the nasolabial fold using magnetic resonance

August 2013 � Vol 144 � Issue 2 American

imaging: implications for facial rejuvenation and facial animationsurgery. Plast Reconstr Surg 1996;98:622-36.

24. Jung YJ, Kim MJ, Baek SH. Hard and soft tissue changes aftercorrection of mandibular prognathism and facial asymmetry bymandibular setback surgery: three-dimensional analysis usingcomputerized tomography. Oral Surg Oral Med Oral Pathol OralRadiol Endod 2009;107:763-71.

25. Cevidanes LH, Styner M, Proffit WR. Three-dimensional superim-position of the skull base for the longitudinal evaluation of theeffects of growth and of treatment. Orthod Fr 2009;80:347-57.

26. Nguyen T, Cevidanes L, Cornelis MA, Heymann G, de Paula LK, DeClerck H. Three-dimensional assessment of maxillary changesassociated with bone anchored maxillary protraction. Am J OrthodDentofacial Orthop 2011;140:790-8.

27. Cevidanes LH, Styner MA, Proffit WR. Image analysis and superim-position of 3-dimensional cone-beam computed tomographymodels. Am J Orthod Dentofacial Orthop 2006;129:611-8.

28. Chung KR, Kim SH, Kang YG, Nelson G. Orthodontic miniplatewith tube as an efficient tool for borderline cases. Am J OrthodDentofacial Orthop 2011;139:551-62.

29. Ford E. Growth of the human cranial base. Am J Orthod 1958;44:498-506.

30. Ford EH. The growth of the foetal skull. J Anat 1956;90:63-72.31. Bjork A, Skieller V. Normal and abnormal growth of the mandible.

A synthesis of longitudinal cephalometric implant studies overa period of 25 years. Eur J Orthod 1983;5:1-46.

32. Melsen B. The cranial base. Acta Odontol Scand 1974;32:86-101.33. Bland JM, Altman DG. Statistical methods for assessing agreement

between two methods of clinical measurement. Lancet 1986;1:307-10.

34. Zierhut EC, Joondeph DR, �Artun J, Little RM. Long-term profilechanges associated with successfully treated extraction and non-extraction Class II Division 1 malocclusions. Angle Orthod 2000;70:208-19.

35. Yasutomi H, Nakata S, Nakasima A, Counts A. Effects of retractionof anterior teeth on horizontal and vertical lip positions in Japa-nese adults with the bimaxillary protrusion. Orthod Waves 2006;65:141-7.

36. Upadhyay M, Yadav S, Nagaraj K, Patil S. Treatment effectsof mini-implants for en-masse retraction of anterior teeth inbialveolar dental protrusion patients: a randomized controlledtrial. Am J Orthod Dentofacial Orthop 2008;134:18-29.

37. Tan TJ. Profile changes following orthodontic correction ofbimaxillary protrusion with a preadjusted edgewise appliance.Int J Adult Orthod Orthognath Surg 1996;11:239-51.

38. Brock RA 2nd, Taylor RW, Buschang PH, Behrents RG. Ethnicdifferences in upper lip response to incisor retraction. Am J OrthodDentofacial Orthop 2005;127:683-91.

39. Rubin LR. The anatomy of the nasolabial fold: the keystone of thesmiling mechanism. Plast Reconstr Surg 1999;103:687-91.

40. Jayaratne YS, Zwahlen RA, Lo J, Cheung LK. Facial soft tissueresponse to anterior segmental osteotomies: a systematic review.Int J Oral Maxillofac Surg 2010;39:1050-8.

41. Bills DA, Handelman CS, BeGole EA. Bimaxillary dentoalveolarprotrusion: traits and orthodontic correction. Angle Orthod2005;75:333-9.

42. Park JU, Hwang YS. Evaluation of the soft and hard tissue changesafter anterior segmental osteotomy on the maxilla and mandible.J Oral Maxillofac Surg 2008;66:98-103.

43. Liu YH, Ding WH, Liu J, Li Q. Comparison of the differences incephalometric parameters after active orthodontic treatment applyingmini-screw implants or transpalatal arches in adult patients withbialveolar dental protrusion. J Oral Rehabil 2009;36:687-95.

Journal of Orthodontics and Dentofacial Orthopedics