Cursos Online de Ortodoncia - Three-dimensional computed … · 2017. 12. 22. · (SARME).6-8 Although the skeletal and dental effects of SARME have been evaluated in several clinical

ORIGINAL ARTICLE

Three-dimensional computed tomographicanalysis of changes to the external featuresof the nose after surgically assisted rapidmaxillary expansion and orthodontictreatment: A prospective longitudinal study

Anders Magnusson,a Krister Bjerklin,b Hyungmin Kim,c Peter Nilsson,d and Agneta Marcussone

J€onk€oping and Link€oping, Sweden, and Boston, Mass

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Introduction: The aim of this prospective, longitudinal study was to evaluate changes to the external shape andform of the nose after surgically assisted rapid maxillary expansion and orthodontic treatment. The changeswere registered using a 3-dimensional computer tomography technique, based on superimposition onthe anterior base of the skull. Methods: The subjects comprised 35 patients (mean age, 19.7 years; range,16.1-43.9 years). Low-dose, helical computerized tomography images were taken at treatment start and afterorthodontic treatment, about 18 months postsurgery. The 3-dimensional models were registered andsuperimposed on the anterior cranial base. Results: There were in general significant widening and overallanterior and inferior displacement of the nasal soft tissues. The changes varied in size and direction. Nocorrelation was found between the initial and final widths of the nose, or between the initial and final widths ofthe nostrils. Conclusions: After surgically assisted rapid maxillary expansion, the most obvious changes tothe external features of the nose were at the most lateral alar bases. The difference in lateral displacementprofoundly influenced the perception of a more rounded nose. Patients with narrow and constrained nostrilscan benefit from these changes. The 3-dimensional superimposition applied in this study is a reliable method,circumventing projection and measurement errors. (Am J Orthod Dentofacial Orthop 2013;144:404-13)

Transverse maxillary hypoplasia is associated pri-marily with functional impairments, such asposterior crossbite, dental crowding, reducednasal respiratory function, or anteroposterior skeletal

r consultant, Department of Orthodontics, Institute for Postgraduatel Education, J€onk€oping, Sweden.ciate professor, Department of Orthodontics, Institute for Postgraduatel Education, J€onk€oping, Sweden.octoral research fellow, Department of Radiology, Brigham and Women'stal, Harvard Medical School, Boston, Mass.ciate professor, Department of Oral and Maxillofacial Surgery, Institute forraduate Dental Education, J€onk€oping, Sweden.ciate Professor, Department of Dentofacial Orthopaedics, MaxillofacialUniversity Hospital, Link€oping, Sweden.thors have completed and submitted the ICMJE Form for Disclosure oftial Conflicts of Interest, and none were reported.rted by Futurum, the Academy for Healthcare, County Council, J€onk€oping,he Medical Research Council of Southeast Sweden.t requests to: Anders Magnusson, Department of Orthodontics, Institutestgraduate Dental Education, Box 1030, SE-551 11 J€onk€oping, Sweden;l, [email protected], January 2013; revised and accepted, April 2013.5406/$36.00ight � 2013 by the American Association of Orthodontists./dx.doi.org/10.1016/j.ajodo.2013.04.013

anomalies, and less with facial esthetics.1-5 A widelyrecognized treatment modality for this condition iscorrection of the underlying skeletal anomaliesby surgically assisted rapid maxillary expansion(SARME).6-8

Although the skeletal and dental effects of SARMEhave been evaluated in several clinical and radiographicstudies, little is known about its effect on the shape andform of the nose.9-11 The soft-tissue changes can bequite obvious, and most clinicians have observedpatients in whom SARME has been associated withpronounced changes to the nose. In some patients,this might be regarded as an untoward side effect; inothers, it could improve facial esthetics.

Soft-tissue changes after corrective orthognathicsurgery have been described in a number ofstudies.12-15 Consistent findings after maxillaryadvancement and maxillary impaction are labialchanges and widening of the nose.16 Most surgeonsare aware of these phenomena and use differenttechniques to reduce these effects.17,18

Delta:1_given nameDelta:1_surnameDelta:1_given nameDelta:1_surnameDelta:1_given namemailto:[email protected]://dx.doi.org/10.1016/j.ajodo.2013.04.013

Magnusson et al 405

The size and shape of the nostrils and the width ofthe alar base are considered to play important rolesin respiration. It is suggested that the site responsiblefor sensing airflow and stuffiness is in the nasalvestibule.19,20 Guenthner et al21 associated modifica-tions in the shape of the external nares with changedairway patency. This finding was supported by Cole,22

who found significant associations between minoralterations in this region and improvement or deteriora-tion in respiratory function. Moreover, Magnusson et al4

concluded that even small changes to the soft tissues inthe most anterior part of a narrow nose can be critical tothe subject's perception of nasal obstruction.

However, with reference to SARME, little is knownabout associated soft-tissue changes and the effectson facial esthetics and respiration.

SARME is often followed by second-stage surgerythat can have a further impact on the soft tissues andrespiration. Thus, it is essential to identify soft-tissuechanges associated with SARME to predict or preventthese effects.

Previous studies on SARME and its effects on softtissues have been limited by the methods available atthe time for quantifying soft-tissue changes. Nganet al23 and Filho et al24 used traditional 2-dimensional(2D) lateral cephalograms. When applied to assesschanges in the soft-tissue profile, 2D cephalometricshave major disadvantages. It is difficult to quantifysoft-tissue alterations adequately from a frontalperspective. Berger et al25 used serial frontal photo-graphs to measure soft-tissue changes, and Ramieriet al26,27 used laser scanning and 3-dimensional (3D)morphometry. In the 3D analysis, the superimpositionmethod is crucial. The major disadvantage of thesemethods is the potential error associated with uncertainsuperimposition, which is related to approximations oraveraged data.

Recently, there have been impressive advancesin computed tomography and imaging techniques,offering new, precise, and accurate approaches to super-imposition.

The purpose of this prospective study was to evaluatechanges to the external features of the nose after SARMEand orthodontic treatment, using a 3D imagingtechnique and registration based on superimpositionon the anterior cranial base.

MATERIAL AND METHODS

Our prospective sample comprised patients sched-uled to undergo SARME. The inclusion criterion forSARME was a real transverse discrepancy according toJacobs et al.28 The magnitude of the skeletal discrepancy(.5 mm) was primarily assessed clinically and on study

American Journal of Orthodontics and Dentofacial Orthoped

models in Class I relationships.1 Transverse assessmentswere also done on computed tomography models.29

This sample was previously evaluated by Magnussonet al4 with reference to skeletal changes after SARME.The same orthodontic, surgical, and radiographicprocedures were applied in both studies.

According to power and size calculations, a priori, theminimum sample size was set at 34 patients, a 5 0.05,and power of 80%. To ensure that the sample size metthese requirements, 40 patients were recruited consecu-tively at the Department of Orthodontics, Institute forPostgraduate Dental Education, J€onk€oping, Sweden,and at the Department of Dentofacial Orthopaedics,Maxillofacial Unit, University Hospital, in Link€oping,Sweden. Participation in the study was voluntary:3 patients declined to participate, and 2 patients wereexcluded because their computed tomography recordswere incomplete. The sample thus comprised 35 patients(14 male, 21 female). The mean age at treatment startwas 19.7 years (range, 16.1-43.9 years).

The study was approved by the ethics committee ofthe Faculty of Health Sciences, Link€oping University, inSweden (reference: M746-04).

The presurgical orthodontic preparation included thefollowing. The maxillary expansion appliance compriseda tooth-borne device activated by means of aconventional hyrax expander (hyrax II; Dentaurum,Ispringen, Germany) with a soldered framework andorthodontic bands (Fig 1). The degree of expansionwas calculated for each patient, including a generalbilateral overexpansion of half a molar-cusp width.The patients were instructed to activate the jackscrew1 turn (approximately 0.225-0.250 mm) twice a dayafter a postoperative latency period of 5 days. Postoper-ative control was scheduled for 12 days postsurgery andincluded a periapical radiograph to ensure clinicallysymmetrical interdental separation and a medialdiastema.30 In patients with a “bad separation”—ie,intra-alveolar separation and risk for periodontalinjuries—prophylactic treatment was initiated. Atthat time, the amount of additional expansion wascalculated.

Surgical treatment was undertaken by 2 experiencedsenior oral and maxillofacial surgeons (P.N. and another)at the Department of Oral and Maxillofacial Surgery,Institute for Postgraduate Dental Education, J€onk€oping,Sweden, and at the Department of DentofacialOrthopaedics, Maxillofacial Unit, University Hospital,Link€oping, Sweden, with a technique similar to thatdescribed by Glassman et al.31

The surgery was carried out under general anesthesiaand nasotracheal intubation. The mucoperiostealincision in the maxillary vestibule extended from the

ics September 2013 � Vol 144 � Issue 3

Fig 1. Skeletal maxillary transverse discrepancyexceeding 5 mm. Tooth-borne maxillary expansionappliance, activated by a conventional hyrax expander(Hyrax II; Dentaurum, Ispingen, Germany).

406 Magnusson et al

right to the left second premolar. Osteotomies wereperformed on the maxillary lateral walls, from thepiriform aperture to the pterygoid plates. The pterygo-maxillary sutures were kept intact. The linings of thefloor and lateral walls of the nasal passage werereflected. A vertical osteotomy at the anterior nasal spineand the median palatal suture was carried out to ensureseparation of the maxillary halves. The hyrax expanderwas activated by 12 turns to verify the success of theosteotomy and to ensure visible symmetrical separation;it was then deactivated by the same amount.

Depending on their physical condition, the patientswere discharged from the hospital on the same day orthe day after surgery.

The postsurgical orthodontic procedures includedthe following. After a mean active expansion period of15 days (range, 11-17 days), the appliance was used asa passive retainer for 90 days. At that time, the hyraxexpander was replaced by a modified transpalatal arch,and fixed appliance treatment began.

On completion of the active treatment phase, thetranspalatal arch was removed, and fixed appliancetreatment continued with stiff rectangular archwires toadjust the transverse width and to control and correctthe buccal root torque of the molars.

All transverse discrepancies were corrected by the endof treatment (mean, 18 months postoperatively), and theorthodontic treatment period was then concluded. Atthis point, 26 patients were referred for second-stageorthognathic surgery. In the remaining 9 patients, thefixed appliance was debonded, and a Hawley plate wasprovided as a retainer.

The computed tomography examinations were un-dertaken at the Center for Medical Image Science andVisualization at University Hospital, Link€oping, Sweden,

September 2013 � Vol 144 � Issue 3 American

and at the Department of Radiology, Ryhov CountyHospital, J€onk€oping, Sweden, 1 week before surgeryand at the end of the active orthodontic treatment phase(mean, 18 months postoperatively).

A helical computed tomography machine (SomatomeSensation 64 CT-scanner; Siemens Medical Solutions,Erlangen, Germany) with a low-dose protocol(CARE dose 4D; Siemens Medical Solutions) was usedat 120 kV and 55 mA. The rotation time was 1 second,and the pitch factor was 0.9, with a collimation of0.6 mm. The increment was 0.3 mm. According to themanufacturer, the isotopic resolution or voxel size was0.33 mm. The patient's head was positioned so thatthe Frankfort horizontal plane was vertical.

The scanned area comprised the anterior cranial baseto the mandibular base. After examination, the imageswere processed at a radiologic workstation (SectraImtec AB, Link€oping, Sweden) with a slice thicknessof 0.75 mm and slice increments of 0.3 mm inKernel H 60s sharp FR, to allow further segmentationand registration.

The data were processed to visualize and measuresoft-tissue changes caused by SARME, using a modifiedversion of a technique described by Cervidanes et al.32,33

This process involves image segmentation, registration,and visualization (Fig 2).

The image registration and superimposition of thepreoperative and postoperative 3D models were donebefore segmentation with a volumetric registrationmethod: specifically, normalized mutual information,based on the anterior cranial base. The cranial fossaeand the ethmoid bone surfaces are regarded as stableareas, with growth completed before puberty.34,35

Once the preoperative and postoperative volumes areregistered, they share the same coordinate system,which compensates for any discrepancies betweenbefore and after volumes, and diminishes the risks ofprojection and measurement errors.

Segmentation is the process of outlining the shape ofa structure—in this case, anterior cranial base, and theouter surfaces of the nasal and midface soft tissues.The segmentation was performed semiautomatically inAMIRA (Mercury Computer System, Berlin, Germany)by an author (H.K.). In the semiautomatic segmentationtechnique, the region of interest is outlined with mouseclicks in the cross-sections of a data set, and algorithms(simple thresholding and region growing) are applied, sothat the path that best fits the edge of the image isshown. With simple thresholding, is it possible to selecta range of gray values (in Hounsfield units, HU). In thisstudy, the lower threshold in bony structures was setto 300 HU, and values above this level were automati-cally selected. The threshold value was interactively

Journal of Orthodontics and Dentofacial Orthopedics

Fig 2. Helical computed tomography images were taken for each patient before and after treatment.Visualization and segmentation involve creation of a 3D model and delineation of the anatomicstructures of interest. The 3D models were superimposed on the anterior cranial base by means ofa volumetric registration method. A graphical user interface-based application (Di2Mesh) was usedfor 3D analysis and measurements.

Magnusson et al 407

adjusted to achieve better contours. Semiautomatictools in AMIRA were effectively used to accelerate theprocess.

A landmark-based, nonrigid mapping technique,thin-plate spline, was used to determine the correspond-ing soft-tissue points between the presurgery andpostsurgery 3D models.36 This was done by a pipelineprocedure according to the method of Kim et al.37

Di2Mesh software (Institute for Surgical Technology& Biomechanics, University of Bern, Bern, Switzerland) isa graphical user interface-based application allowing theuser to compute surface-to-surface distances in anyspecified direction and visualize them with a colormap.37

Fifteen validated landmarks were used for themeasurements (Fig 3).12,38,39 The landmarks wereidentified and digitized by the first author (A.M.). Thenonrigid transformation model, thin-plate splinedeformation, and closest-point matching were used toshow displacements.37 The software (Di2Mesh)computed the closest-point relationship between thepresurgical and postsurgical landmarks in a 3DEuclidean space coordinate system.


The displacement vectors were normalized with theFrankfort horizontal plane coordinate system accordingto the method of Xia et al.40 The transversal plane isdefined by right and left porion, and the averagedcoordinates of right and left orbitale. The frontal planeis perpendicular to the transversal plane, through rightand left porion. The sagittal plane is perpendicular tothe transversal and frontal planes, through nasion.This means that the zero point of the Frankforthorizontal plane will be the center of left and rightporion. As shown in Figure 4, lateral displacement onthe x-axis, superior displacement on the y-axis, andanterior displacement on the z-axis were recorded aspositive values.

The transverse displacements of corresponding land-marks on the x-axis were also summarized. TheEuclidean distances—ie, the shortest distances between2 landmarks—were measured to evaluate the heightand width of the nose and nostrils (Fig 5).

Ten computed tomography volumes were randomlyselected. The anatomic landmarks were located anddigitized in each 3D model. The same observer(A.M.) repeated the procedure 4 weeks later, and the


Fig 3. Landmarks:1, pronasale, the most anteriormidpoint of the nasal tip; 2 and 3, alar right and left, themost lateral point on each alar contour; 4 and 5, alarcurvature right and left, the point located at the facialinsertion of each alar base; 6, columella, the midpointon columella at the level of the superior nostrils(landmarks 8 and 9); 7, subnasale, the midpoint onthe nasolabial soft-tissue contour between thecolumella crest and the upper lip; 8 and 9: nostril superiorright and left, the most superior points of the nostril;10 and 11, nostril inferior right and left, the most inferiorpoints of the nostril; 12 and 13, nostril lateral rightand left, the most lateral points of the nostril; 14 and 15,alar base right and left, the most lateral points of thealar base.

Fig 4. The displacement vectors were normalized withthe Frankfort horizontal plane coordinate system andrecorded as positive values laterally in the x-axis, superi-orly in the y-axis, and anteriorly in the z-axis.

408 Magnusson et al

displacements of the landmarks were calculated. Theerror of the measurements was calculated by intraclasscorrelation coefficient (ICC) for single measurements;this is an expression of intraobserver reliability. An ICCabove 0.75 indicates excellent reliability. The ICC valueswere between 0.851 and 0.992. Landmarks 1, 6, and 7 inthe midline showed the weakest ICC values.

Statistical analysis

Statistical analyses were undertaken using theStatistical Package for the Social Sciences III (version20.0; SPSS, Chicago, Ill). The distribution of data wastested with the 1-sample Kolmogorov-Smirnov test.The results showed normal distribution of the data,but because of the sample size, nonparametric testswere also warranted. Median values and percentileswere used to describe the changes and distributions.The Wilcoxon signed rank nonparametric test was usedto evaluate pretreatment and posttreatment differences.The level of significance was set at P \0.05. TheSpearman rho was applied to assess the correlationsbetween the changes at the nose.


RESULTS

There were in general significant widening andoverall anterior and inferior displacement at the nose.

For the x-axis (lateral displacement, left and right), alllandmarks at the alar wings showed lateral displacement(Table I). The displacements on the left and right sideswere symmetrical and most obvious at the lateral alarbases (Fig 3; landmarks 14 and 15). The amount ofdisplacement of the lateral alar bases decreasedgradually toward pronasale and toward the facialinsertion of the nostrils.

The most pronounced lateral change to the nostrilswas at the utmost lateral point of the inner contour ofthe nostrils, which decreased in the anterior and inferiordirections of the x-axis.

Landmarks 1, 6, and 7 in the midline (Fig 3) showedno significant lateral displacements; neither did land-marks 10 and 11 at the most inferior point of the nostrils(Fig 3). There were significant correlations (P \0.001)between the lateral displacements at the alar wingsand between the lateral displacements in the nostrils.

For the y-axis (superior and inferior displacement),most landmarks showed moderate inferior displacement(Table I). The most significant displacements, albeitminor, were found at pronasale and subnasale (Fig 3;landmarks 1 and 7). The amounts of displacement atpronasale and subnasale decreased gradually in theposterior and lateral directions on the y-axis.

For the z-axis (anterior and posterior displacement),the most significant and obvious displacement occurred


Fig 5. A, The shortest distances without orientation in space were measured for nose height(landmarks 1 and 7), nose width I (landmarks 2 and 3), nose width II (landmarks 4 and 5), and nosewidth III (landmarks 14 and 15); B, and for nostril length (landmarks 8 and 10, and 9 and 11), nostrilwidth I (landmarks 12 and 13), and nostril width II (landmarks 10 and 11).

Table I. Median displacements and changes at the nose measured at 15 landmarks (in mm) (Fig 3)

Landmark

X-axis Y-axis Z-axis

Medianchange p10 p90

Wilcoxontest


Wilcoxontest


Wilcoxontest

1 0.11 �0.64 0.86 NS �0.26 �1.40 0.28 z 0.03 �0.14 0.80 y2 1.10 0.06 1.89 z �0.25 �1.34 1.23 NS 0.46 �1.23 2.28 *3 0.70 �0.13 1.91 z �0.04 �1.85 1.04 NS 0.63 �0.72 2.39 z4 0.59 �0.62 2.16 y �0.27 �1.84 1.06 NS 1.14 �0.17 2.82 z5 0.58 �1.22 1.85 * �0.48 �1.91 1.11 * 1.18 �0.40 3.45 z6 0.10 �0.54 1.38 NS �0.11 �1.20 0.61 NS 0.41 �0.59 2.04 y7 0.09 �1.22 1.20 NS �0.51 �2.28 0.59 y 0.07 �1.32 1.41 NS8 0.42 �0.47 1.67 NS �0.20 �1.52 1.00 NS 0.26 �0.36 1.57 y9 �0.10 �1.44 1.00 NS �0.35 �1.29 0.62 * 0.22 �0.50 1.31 *

10 0.35 �1.32 2.26 NS �0.19 �1.49 1.23 NS 0.85 �0.85 1.94 z11 0.29 �1.04 1.87 NS �0.12 �1.47 0.76 NS 1.07 �0.23 2.37 z12 0.81 �0.42 2.40 z 0.48 �1.79 0.71 y 0.18 �2.06 1.44 NS13 0.67 �0.33 1.76 z 0.47 �1.43 1.10 * 0.43 �0.94 2.12 y14 1.47 0.30 2.90 z 0.10 �1.12 1.66 NS 1.36 0.05 2.76 z15 1.41 0.46 2.60 z �0.04 �1.62 1.03 NS 1.98 0.37 3.25 z

Displacements were recorded as positive values laterally in the x-axis, superiorly in the y-axis, and anteriorly in the z-axis.p10, 10th percentile; p90, 90th percentile; NS, nonsignificant.*P\0.05; yP\0.01; zP\0.001.

Magnusson et al 409

anteriorly (Table I), particularly at landmarks near thefacial insertion (Fig 3; landmarks 4, 5, 10, 11, 14, and15). This anterior displacement was, however, notevident at subnasale (Fig 3; landmark 7), which showeda contrasting, posterior displacement.

The Euclidean distance (the shortest distancebetween 2 landmarks) was analyzed and calculated forheight and width of the nose and nostrils (Fig 5; TableII). Nose height, measured between pronasale andsubnasale (Fig 5, A), remained unchanged, but a


significant and evident widening was apparent at thealar wings and alar base (Fig 5, A; nose width I, nosewidth III). The nose width at the facial insertion persistedunchanged (Fig 5, A; nose width II). A significantwidening of the nostrils was obvious at the lateral alarwings (Fig 5, B; nostril width I) but not at the lowestpoint (Fig 5, B; nostril width II). The nostril lengthremained unchanged. No correlation was foundbetween the initial and final widths of the nose, orbetween the initial and final widths of the nostrils.


Table II. Median changes between landmarks withoutorientation in space (in mm) (Fig 5)


Wilcoxontest

Nose height(landmarks 1 and 7)

0.18 �1.38 2.15 NS

Nose width I(landmarks 2 and 3)

1.66 0.27 3.13 *

Nose width II(landmarks 4 and 5)

1.01 �0.65 2.72 NS

Nose width III(landmarks 14 and 15)

3.09 1.56 4.70 y

Nostril height(landmarks 8 and 10,9 and 11)

�0.47 �1.12 0.83 NS

Nostril width I(landmarks 12 and 13)

1.47 �0.08 3.19 y

Nostril width II(landmarks 10 and 11)

0.68 �1.51 2.29 NS

p10, 10th percentile; p90, 90th percentile; NS, nonsignificant.*P\0.01; yP\0.001.

410 Magnusson et al

DISCUSSION

The results show that after SARME there is a true 3Dchange in the nose: not only widening of the nose, butalso anterior and inferior displacement of the wholenasomaxillary complex. The displacements vary in sizeand direction, and the complexity of the changes isdifficult to assess without a valid and reliable method.

The computed tomography models and the refined3D methodology used in this study, with volumetricregistration based on the anterior cranial base, offerprecise and accurate superimpositions, which areessential for quantifying and determining spatialdisplacements. The vectors were normalized with theFrankfort horizontal plane coordinate system, whichallows analysis of changes in each direction. The 3Dbreakdown of the changes facilitates greater under-standing of the variations and might offer someindication of possible causes. Displacements withoutorientation in space were used to estimate and correlatethe magnitude of changes.

A crucial factor for correct analysis is the validity andreliability of the measurements: ie, the accuracy of theselected landmarks and the error of the measurements.Landmarks for measurement were selected to show thedisplacements in different areas with good reliability. TheICC value was high (.0.977) for extreme landmarks atthe inner andouter contours of the alarwings. TheweakestICC scores, although still above 0.851, were for landmarksin the midline (pronasale, columella, and subnasale).

A source of bias in measuring soft tissues is theirsoftness and adaptability. The immediate postoperative


swelling after SARME will subside within a few weeks,but residual swelling will persist.41 To prevent this sourceof error, the soft-tissue registration was done at the endof treatment, at a mean of 18 months postoperatively.

The most obvious amount of widening was found atthe most lateral alar base (Fig 5, A; nose width III), amean of 2.88 mm, representing a mean increase of 9%of the initial width. Berger et al25 reported an increasein the nasal base width of up to 2 mm, and Ramieriet al27 found a mean widening of 1.4 mm. The wideningin our study was more pronounced than the values inprevious studies. This discrepancy cannot be readilyexplained but might be attributable to such factors asvariations in surgical techniques or differences in theaccuracy and reliability of the measuring methodsapplied in the studies.

Because candidates for SARME are patients withtransverse skeletal discrepancies, it would be logical toexpect most changes to occur in a transverse direction.The results showed lateral displacements, but thesewere accompanied by anterior and inferior displace-ments. A possible and rational explanation is theoccurrence of corresponding displacements in the softand hard tissues. According to Chung et al42 and Bretoset al,43 the anterior displacement in our study could berelated to the anterior displacement of the underlyingskeletal structures. However, Lagrav�ere et al44 foundno evidence for either anterior or inferior skeletaldisplacement after SARME. To resolve such contradic-tory findings, further studies are warranted, applyingappropriate modern measuring techniques to documentmaxillary displacement after SARME and correlationswith soft-tissue changes.

The soft-tissue changes not only are thus related tothe extent or direction of the skeletal displacements,but also are more likely multifactorial consequences ofdifferent elements, such as the surgical technique, theamount of soft tissues, the facial type, or a gain or lossin weight. It is nevertheless important for the clinicianto be aware of soft-tissue changes associated withSARME. Ideally, it should be possible to predict thetreatment outcome to prevent unwanted side effects.

On the x-axis, the most significant displacementswere found at the lateral parts of the nose, primarily atthe alar base (Fig 3; landmarks 14 and 15), secondarilyat the lateral alar wings (Fig 3; landmarks 2 and 3),and less significantly, at the insertions of the alar wings(Fig 3; landmarks 4 and 5). No significant lateral changeswere found in the midsagittal plane.

The difference in lateral displacements between thelateral landmarks played an essential role in theperception of a more rounded shape and an increasedsize of the nose. This, combined with more circular


Magnusson et al 411

nostrils, made the nostrils more visible in the frontal viewand gave a sense of an increased nasolabial angle, eventhough an overall anterior and inferior displacement ofthe nasomaxillary complex was evident. This outcomemight be attributable to the surgical technique used.The osteotomies were performed on the maxillary lateralwalls, from the piriform aperture to the pterygoid plates,including detachment of the mucosa and soft tissue onthe nasal floor and lateral walls. The detachment ofsoft tissues at the insertion of the alar wings (Fig 3; land-marks 4 and 5) might explain why this displacement wasmuch less pronounced than that in the attached softtissues at the lateral alar bases (Fig 3; landmarks 14and 15).

Whether this widening and the overall anterior andinferior displacement of the nose are beneficial to thepatient is a clinical judgment. The main purpose of thesurgical techniques available for controlling the widthof the nose is to diminish the width at the anterior inser-tions of the alar wings and nostrils. These techniques donot take into account the widening at the attachedlateral alar base.45 Such a procedure should be usedwith caution after SARME when there is a risk of anunesthetic accentuated rounding of the anterior nose.

The most statistically significant changes were foundin the anterior direction (z-axis). The changes were inmost cases quite minor, but the uniformity in directionand the significance nevertheless demonstrate anteriormovement of the nose. The magnitude of the anteriordisplacements varied but, in accordance with the lateraldisplacement on the x-axis, was most obvious at themost lateral alar base (Fig 3; landmarks 14 and 15).

The displacements on the y-axis were less significant,small, and varied in direction and can perhaps be relatedto factors other than the effects of SARME. The mostsignificant displacements on the y-axis were found atsubnasale and pronasale. We found no correlationbetween the initial and final nostril widths, or betweenthe initial and final nose widths. This lack of correlationhighlights the complexity of all affected components.There is, however, a clear tendency toward overall lateral,anterior, and inferior displacement of the nose; theclinician should take these into account in treatmentplanning.

Some measurements were of particular note. Theheight of the nose measured from subnasale topronasale as well as the length of the nostrils remainedunchanged. These findings indicate increased nostrilarea associated with widening of the nostrils. Thechange in nostril shape from a narrow slit to a moreovoid or circular form postoperatively was obvious andsignificant. In this context, it is of interest that narrownostrils are associated with nasal obstruction,46 and


widening is associated with a subjective perception ofimproved nasal function.4 Consequently, patients withnarrow and constrained nostrils benefit from thesoft-tissue changes.

These data consisted of measurements of displace-ments at specific digitized landmarks at the nose. TheDi2Mesh software application can, without landmarks,also analyze any specified displacement and visualizethe displacements using a color map. The colorvisualization of the displacements in this softwareshowed major changes in the paranasal region. Thesechanges were not analyzed because of the lack ofreliable and valid landmarks in this area, but they willhave an indirect impact on the appearance of the noseand the midface. Furthermore, at the time of registra-tion, uncertain lip posture precluded evaluation ofchanges to the upper lip.

With respect to radiation exposure, it is importantthat ethical aspects are addressed, not only in thecontext of clinical studies, but also in routine practice.Radiation exposure should always follow the “as lowas reasonably achievable” principle.47 In this study, theassessed risk of radiation exposure was weighed againstachieving the required information: a 3D assessment ofchanges to the external shape and form of the nose. Thesample comprised nongrowing patients scheduled toundergo SARME; additional 2D images would haveincreased their radiation dose but provided only limitedor partial diagnostic information.

To secure a high diagnostic advantage in treatmentplanning, a low-dose helical computed tomographymachine was used, with a low-dose protocol. Cone-beam computed tomography scans would have beenan acceptable alternative but were not available at thetime. The submission to the board of ethics for approvalof the study included a discussion of radiation exposure.

CONCLUSIONS

There were in general significant widening andoverall anterior and inferior displacement of allnasomaxillary soft tissues.

The changes were most obvious laterally andanteriorly on the x-axis and y-axis.

There was variety in the size of the displacements thatrounded the shape of the nose in the frontal view.

Therewas significantwideningof thenostrils andan in-crease in nostril area. Patients with narrow and constrainednostrils can benefit from the soft-tissue changes.

There were no correlations between the initial andfinal widths of the nostrils, or the initial and final widthsof the nose.

It is questionable whether an alar cinch suture willprevent widening at the alar base.


412 Magnusson et al

ACKNOWLEDGMENTS

We thank Gunvor Johansson for her excellentassistance; Mauricio Reyes, head of the Medical ImageAnalysis group at the Institute for Surgical Technologyand Biomechanics at the University of Bern, Bern,Switzerland; Birgit Ljungquist, our statistician; andRune Lindsten, head of the orthodontic department ofThe Institute for Postgraduate Dental Education,J€onk€oping, Sweden.

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Three-dimensional computed tomographic analysis of changes to the external features of the nose after surgically assisted r ...Material and methodsStatistical analysis

ResultsDiscussionConclusionsAcknowledgmentsReferences

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Cursos Online de Ortodoncia - Three-dimensional computed … · 2017. 12. 22. · (SARME).6-8 Although the skeletal and dental effects of SARME have been evaluated in several clinical