Facial Asymmetry: Etiology, Evaluation, and Management · The etiology includes congenital disorders, acquired diseases, and traumat-ic and developmental deformities. The causes of

341Review Article

Facial Asymmetry: Etiology, Evaluation, and Management

You-Wei Cheong, MD; Lun-Jou Lo, MD

Facial asymmetry is common in humans. Significantfacial asymmetry causes both functional as well as estheticproblems. When patients complain of facial asymmetry, theunderlying cause should be investigated. The etiologyincludes congenital disorders, acquired diseases, and traumat-ic and developmental deformities. The causes of many casesof developmental facial asymmetry are indistinct. Assessmentof facial asymmetry consists of a patient history, physicalexamination, and medical imaging. Medical imaging is help-ful for objective diagnosis and measurement of the asymme-try, as well as for treatment planning. Components of soft tis-sue, dental and skeletal differences contributing to facialasymmetry are evaluated. Frequently dental malocclusion,canting of the occlusal level and midline shift are found.Management of facial asymmetry first aims at correcting theunderlying disorder. Orthognathic surgery is performed for the treatment of facial asymme-try combined with dental occlusal problems. A symmetrical facial midline, harmoniousfacial profile and dental occlusion are obtained from treatment. Additional surgical proce-dures may be required to increase or reduce the volume of skeletal and soft tissue compo-nents on both sides to achieve better symmetry. (Chang Gung Med J 2011;34:341-51)

Key words: facial asymmetry, evaluation, surgical treatment

From the Department of Plastic and Reconstructive Surgery and Chang Gung Craniofacial Research Center, Chang Gung MemorialHospital at Linkou, Chang Gung University College of Medicine, Taoyuan, Taiwan.Received: Feb. 15, 2011; Accepted: Apr. 25, 2011Correspondence to: Dr. Lun-Jou Lo, Department of Plastic and Reconstructive Surgery, Chang Gung Memorial Hospital at Linkou.5, Fusing St., Gueishan Township, Taoyuan County 333, Taiwan (R.O.C.) Tel.: 886-3-3281200 ext. 2855; Fax: 886-3-3285818; E-mail: [email protected]

Perfectly bilateral face and body symmetry islargely a theoretical concept that seldom exists in

living organisms. Right-left differences occur every-where in nature where two bilateral congruent partspresent in an entity. Humans frequently experiencefunctional as well as morphological asymmetries,e.g. right and left handedness as well as preferencefor one eye or one leg in performing a particulartask. Some of these asymmetries are embryonicallyor genetically determined and encoded in the centralnervous system.(1) Preferential laterality for someanomalies is striking, such as cleft lip, which occurs

more commonly on the left side. Left-right toothcrown size asymmetry, evident by measurement butnot by visual inspection, is also a normal state in thegeneral population.(2) Slight facial asymmetry can befound in normal individuals, even in those with aes-thetically attractive faces. This minor facial asymme-try is common, usually indiscernible and does notrequire any treatment. The point at which ‘normal’asymmetry becomes ‘abnormal’ cannot be easilydefined and is often determined by the clinician’ssense of balance and the patient’s sense of imbal-ance.(1) By collating photographs of the right and left

Dr. Lun-Jou Lo

Chang Gung Med J Vol. 34 No. 4July-August 2011

You-Wei Cheong, et al Facial asymmetry

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sides of a ‘normal’ face with their respective mirrorimages, three faces can be visualized; the originalface, the two left sides, and the two right sides. Oftenthese three faces from the same individual are dis-tinctly different.(3) An example using 3-dimensionalphotography is demonstrated in Fig. 1.

It has been reported that in cases of minor facialasymmetry, the right hemiface is usually wider thatthe left hemiface with the chin deviated to the left.(4)

Facial asymmetry affects the lower face more fre-quently than the upper face. Severt and Proffitreported frequencies of facial laterality of 5%, 36%and 74% in the upper, middle and lower thirds of theface.(5) The lower part of the face deviates more fre-quently and at greater distances than the upper andmiddle parts. One explanation is that the period ofgrowth of the mandible is longer. Chew et al reportedasymmetry in 35.8% of 212 patients with dentofacialdeformities, with the majority of cases in patientswith class III occlusal deformity.(6,7) He suggestedthat special attention be paid to class III patients todetect any asymmetry. Class III is more common inAsians than in Caucasians, so is a reasonableassumption that there are more patients with facial

asymmetry among the normal population in Asiathan in Western countries.

Etiology of facial asymmetryFacial asymmetry may be associated with class I

occlusion, but is more frequently associated withclass II and III occlusions. In some instances theasymmetry is secondary to condylar hyperplasia orhypoplasia, ankylosis of the temperomandibularjoint, displaced condylar fractures, or hemifacialmicrosomia. The etiology of facial asymmetry formany other cases is, however, still unknown. Facialasymmetry can be summarized and divided intothree main categories, (1) congenital, originating pre-natally; (2) developmental, arising during growthwith inconspicuous etiology; and (3) acquired,resulting from injury or disease, as shown in theTable 1.(8-10) Kawamoto et al divided the causes of anidiopathic laterally deviated mandible into 2 cate-gories.(11) The first group involves alteration of thecranial base and glenoid fossa which leads to dis-placement of the mandible. This includes musculartorticollis, unilateral coronal craniosynostosis anddeformational plagiocephaly.(12-15) The second catego-

Fig. 1 (A) This 3-dimensional photograph of a normal adult man taken by a 3 dMD system shows a grossly symmetrical face. Theface image was adjusted in the standard frontal view. The facial midline was defined, and a mirror image technique was performed.(B) This is a manipulated image in which the right side of the face was replaced by a mirror image of the left side. Likewise (C) thisis an image of the two right sides of the face. (B) and (C) represent perfectly symmetric faces. The original image and the twomanipulated images look different. Comparisons between (B) and (C) show apparent differences, notably in the cheek fullness,mouth angles, and chin.

A B C



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ry involves condylar anomalies which result inhypoplastic or hyperplastic growth of the condyle.Examples include condylar fracture, condylar hyper-plasia, and condylar arthritis and hemifacial microso-mia.(16,17)

The developmental type of facial asymmetry isidiopathic and non-syndromic in nature, and is notuncommonly seen in the general population. Theasymmetry is not observed at birth or in infancy, andappears gradually, usually becoming apparent in theteenage years. There is no obvious history of facialtrauma or detectable disease causing the asymmetry.One possible source is habitual chewing on one side,which is responsible for increased skeletal develop-ment on the ipsilateral side.(18) Persistent sleep on oneside may be another cause. Haraguchi et al suggestedthat the etiology of facial asymmetry can be dividedbetween those with genetic origins and those withenvironmental origins.(19) Neurofibromatosis is onecause of facial asymmetry caused by genetic factors.It is also noted that in cleft lip and palate, the pathol-ogy more often occurs on the left side and this phe-nomenon probably has a genetic basis.(20) Intrauterinepressure on the fetus head, as well as pressure in thebirth canal during parturition can cause molding ofthe skull bones and facial bones, causing observablecraniofacial asymmetry. However this problem isusually transient and the skull and facial bones returnto their normal shape within a few weeks to fewmonths. Non-hereditary conditions that cause facialasymmetry include osteochondroma of the mandibu-lar condyle, which may affect the form and function

of the temporomandibular joint, which in turn causesmandibular deviation and facial asymmetry.(21-24)

Trauma, arthritis and infection within the temporo-mandibular joint can lead to ankylosis of the joint.(25)

In a growing child, this condition can lead to unilat-eral mandibular underdevelopment on the affectedside.(26) Cohen used the term ‘hemi-asymmetries’ indiscussion of craniofacial asymmetry. He furtherclassified these conditions into hemi-hyperplasia,hemi-hypoplasia, hemi-atrophy and other miscella-neous entities.(27)

Clinical implicationsBased on the craniofacial structures involved,

facial asymmetry can be classified into dental, skele-tal, soft tissue and functional components. Commoncauses of dental asymmetry are early loss of decidu-ous teeth, a congenital missing tooth or teeth, andhabits such as thumb sucking. Skeletal asymmetrymay involve one bone such as the maxilla ormandible, or it may affect a number of skeletal struc-tures on one side of the face, as in hemifacial micro-somia. When one side of osseous development isaffected, the contralateral side will most inevitablybe influenced resulting in compensational or distort-ed growth. Muscular asymmetry can occur in condi-tions such as hemifacial microsomia and cerebralpalsy. Abnormal muscle function, as in masseterhypertrophy, can itself cause an asymmetricalappearance of the face, as well as contribute to dentaland skeletal asymmetry because of abnormal musclepull. Fibrosis of the sternocleidomastoid muscle asseen in torticollis may create evident craniofacialdeformation if left untreated for a period of time.(15)

Not only facial but also endocranial morphology isaffected and distorted. The deformation becomesmore severe with time. Functional asymmetry mayresult from the mandible being deflected laterally ifocclusal interferences prevent proper intercuspationin the centric position. These functional deviationsmay be caused by a constricted maxillary arch or alocal factor such as a malpositioned tooth. In somecases, temporomandibular joint derangement, suchas an anteriorly displaced disc, may result in a mid-line shift during mouth opening caused by interfer-ence in mandibular translation on the affected side.However, a combination of these factors is often pre-sent. Proper evaluation is needed to arrive at the cor-rect diagnosis. Reyneke et al recommended a classi-

Table 1. Etiology of Facial Asymmetry

Congenital Developmental Acquired

Cleft lip and palate Cause unknown Temperomandibular joint

ankylosis

Tessier craniofacial cleft Facial trauma

Hemifacial microsomia Childhood radiotherapy

Neurofibromatosis Fibrous dysplasia

Torticollis Other facial tumors

Craniosynostosis Unilateral condylar

hyperplasia

Vascular disorders Romberg’s disease

Others Others



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fication system based on the positions of threeanatomical areas, namely the maxilla, mandibularbody and mandibular symphysis, in relation to thefacial midline, as well as the presence of occlusalcanting. The authors provided a simple method toidentify an appropriate orthodontic and surgicalapproach for each specific type of asymmetry.(10)

Clinically detectable facial asymmetry may beassociated with more occult abnormalities elsewherein the facial skeleton. For example clinically evidentchin deviation may be associated with significanthorizontal and vertical asymmetry in paired skeletallandmarks in the upper, middle and lower face. Thismight complicate planning by distorting the refer-ence plane.(28) Facial asymmetry may cause a numberof problems in patients, including undesirablecosmesis, malocclusion, altered movement of thetemporomandibular joint and other temporomandibu-lar joint problems such as pain and clicking.

Evaluation of facial asymmetryPatients with facial asymmetry are evaluated

through clinical assessment, photography, cephalog-raphy, and sometimes 3-dimensional computedtomography. Clinical examination reveals asymmetryin the sagittal, coronal and vertical dimensions. Itremains the most important diagnostic tool in theevaluation of facial asymmetry. Clinical assessmentstarts with ascertaining the patient’s chief complaintand evaluating the medical history. Clinical examina-tion involves visual inspection of the entire face,palpation to differentiate soft tissue and bonydefects, comparison of the dental midline with thefacial midline, inspection of symmetry between thebilateral gonial angle and mandibular body lowerborder, determination of the amount of gingival showper side, and evaluation of malocclusion, occlusalcanting, inclination of the anterior teeth, open bites,maximal interincisal opening, mandibular deviation,and the temporomandibular joint. However bodyposture, mannerisms and hairstyle may hide asym-metry and mislead the treatment plan. (29) Mostpatients notice horizontal or transverse discrepancymore often than vertical and sagittal asymmetry.

The dental midline should be evaluated in thefollowing positions: opening mouth, in centric rela-tion, at initial contact, and in centric occlusion. Truedental and skeletal asymmetry will show similarmidline discrepancies in centric relation and in cen-

tric occlusion. Asymmetry due to occlusal interfer-ence may result in a mandibular functional shift oninitial tooth contact. The shift can be either in thesame direction or opposite direction of the dental orskeletal discrepancy and may actually accentuate ormask the asymmetry. In addition, functional asym-metry related to temporomandibular joint derange-ment should be excluded. The presence of a cantedocclusal plane could be the result of a unilateralincrease in the vertical length of the mandibularramus and condyle. The maxilla and temporal bonesupporting the glenoid fossa could be at differentlevels on each side of the head. Clinically the cantedocclusal plane is readily detected by asking thepatient to bite on a tongue blade to determine how itrelates to the inter-pupillary plane. At times, patientstilt their heads with a canted orbital level to compen-sate the lower facial asymmetry, and orbital cantingimproves after correction of the facial asymmetry.

Vertical skeletal asymmetry associated with aprogressively developing unilateral open bite may bethe result of condylar hyperplasia or neoplasia.Asymmetry in the bucco-lingual relationship, e.g. aunilateral posterior cross bite, should be carefullyassessed to determine whether the cause is skeletal,dental or functional. Dental arch asymmetries couldoccur because of local factors such as early loss of adeciduous tooth or they could be associated with therotation of the entire dental arch and its supportingskeletal base. Assessment of the overall shape of themaxillary and mandibular arches from an occlusalview may disclose not only side to side asymmetriesbut also differences in the bucco-lingual angulationof the teeth. It is important to realize that expansionof the dental arch in the presence of skeletal constric-tion may adversely affect the stability of the correc-tion. Arch asymmetry could also be due to rotationof the entire maxilla or mandible. In addition to bilat-eral structural comparison, deviation of midlinestructures such as the dorsum and tip of the nose, thephiltrum and the chin point needs to be determined.

In many cases, clinical examination needs to besupplemented by other diagnostic modalities such asdental casts, face bow transfer and various imagingtechniques to accurately localize the asymmetricstructures. In radiographic assessment, a number ofprojections are available to identify the location andcause of facial asymmetry. The lateral view oncephalometry provides limited useful information on



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asymmetry in the ramal height, mandibular lengthand gonial angle. It is limited by the fact that theright and left structures are superimposed on eachother and there are different distances from the filmand x-ray source resulting in significant differencesin magnification. On the other hand, the panoramicview can be a useful projection. The skeletal anddental structures of the maxilla and mandible aresubjectively assessed with relative ease. The pres-ence of gross anomalies, and supernumerary or miss-ing teeth can be detected. The shape and height ofthe mandibular ramus and condyles on both sides canbe compared. The cephalometric postero-anteriorprojection is a valuable tool in the study of the rightand left structures since they are located at equal dis-tance from the film and x-ray source (Fig. 2). Thepostero-anterior view can be obtained at the centricocclusion and open mouth positions to determine theextent of functional deviation. It is recommendedthat a horizontal line be drawn through the bilateralzygomatico-frontal sutures to act as the horizontalaxis in the construction of the horizontal and mid-sagittal reference planes. A vertical line perpendicu-lar to this horizontal axis is drawn to pass through

the crista galli. This vertical line approximates theanatomic midsagittal plane of the head. The nasionand the anterior nasal spine are noted to fall verynear this plane 90% of the time.(30) Perpendicularlines from the bilateral structures can now be drawnand the distance from the midsagittal reference linecan be measured and compared to determine discrep-ancies in height as well as the distances between thebilateral structures and the midline. In addition, themaxillary and mandibular dental midlines are com-pared to the skeletal midline. Stereophotogrammetryusing two or more cameras, configured as a stereo-pair to generate a 3-dimensional image of the face bytriangulation, has been reported. This provides a use-ful three-dimensional assessment of facial soft tissueasymmetry before and after orthognathic surgery.(31)

More recent devices for 3-dimensional photographyhave been used (Fig. 3). The image can be used forcomparison and quantitative measurement. The pre-cision and accuracy of the 3-dimensional pho-tographs have been validated.(32-34) The soft tissueimages captured from 3-dimensional photogramme-try are comparable to those obtained from traditionalcephalogrammetry.(35) Other radiographic modalities

A B

Fig. 2 A posteroanterior view on cephalography of a patient with right temperomandibular joint ankylosis after release and resec-tion of the right condyle shows marked deviation of the mandible to the right side and soft tissue asymmetry (A). The patientreceived a LeFort I osteotomy for leveling, a left sagittal split of the mandibular ramus for rotation, a release of the right tempero-mandibular joint and lengthening of the right ramus using a costochondral graft, and a genioplasty for lengthening and advance-ment, showing improvement of the skeletal as well as soft tissue contour and symmetry (B).



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in the assessment of facial asymmetry includetomography and computed tomography (CT). CTscans both in 2-dimensional and 3-dimensionalviews can provide excellent details necessary forproper diagnosis and treatment. In addition, threedimensional CT images can also provide informationfor the fabrication of three-dimensional acrylic skele-tal models to facilitate evaluation and surgical plan-ning.(36) Cone beam CT scanning has become popularin many dental and maxillofacial centers.

Planning and managementDecisions about intervention for dentofacial

deformities depend on patient awareness of the aes-thetic problem, the extent of the occlusal deformity,and concomitant sagittal or vertical jaw imbalance.(28)

Facial asymmetry may involve dental, skeletal andsoft tissue components and a combination of ortho-dontic treatment and orthognathic surgery may beindicated. Treatment of facial asymmetry in preado-lescent children is often difficult with unpredictableresults. Growth modification with functional appli-ances has been problematic and the use of a bite-block rarely prevents the need for other treatmentmodalities.(29) A growing patient with mild asymme-try and a functional condyle should receive earlyorthodontic treatment and be allowed to finishgrowth before surgery is undertaken.

True dental asymmetry can be managed by

orthodontic treatment alone. Asymmetric extractionsequences and asymmetric mechanics can beemployed to correct dental arch asymmetry.Prosthodontic restoration may be indicated in pro-nounced tooth irregularities. Mild functional devia-tion can be managed by minor occlusal adjustments.More severe deviations may need orthodontic treat-ment to align the teeth to obtain proper function. Inaddition to routine presurgical anteroposterior ortho-dontic decompensation, intentional transverse ortho-dontic decompensation may also be required inpatients with asymmetry.(37) Unilateral vertical maxil-lary excess and mandibular asymmetry are usuallyassociated with an occlusal cant. This explains whymost asymmetries cannot be treated with single-jawsurgery.

More severe asymmetries require a combinationof orthodontic and orthognathic management.Clinical practice has shown that surgical correctionof the maxillomandibular bony complex may not dif-fer appreciably for etiologically different asymme-tries with similar clinical presentations, except thatmore emphasis is placed on the frontal view duringthe planning.(10) Correct surgical treatment beginswith a proper diagnosis with accurate evaluation ofall facial dimensions. Failure to recognize asymme-try until after surgery is viewed by most patients aspoor treatment. However the surgical correction offacial asymmetry is challenging because the asym-

A B

Fig. 3 The 3-dimensional photograph shown in Figure 1A was used to overlap the mirror image of the left side of face on the rightside of the face (A). A color map illustrates the differences in depth, showing asymmetry or deformity of the facial contour on bothsides. Quantitative differences are shown on the right upper inset scale map. A mirror image of the right side of the face overlappingthe left side of the face and the differences are shown in (B).



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metry may involve hard and/or soft tissue in anycombination of dimensions. It may involve the max-illa, mandible, symphysis, other parts of the dentofa-cial skeleton or any combination of these. It is theeffective treatment of the hard tissues that bringsabout the most dramatic change, as soft tissue gener-ally follows underlying bones. Otherwise isolatedsoft tissue deformities are usually corrected during orafter skeletal correction.(38) Another problem in thecorrect planning of treatment is the aspect of growthand development. As a consequence, the planningand extent of surgical correction should be tailored,and secondary surgery could be needed. Unilateralcondylar hyperplasia with excessive growth may per-sist until the age of 23 years. Romberg disease mayprogress further after 18 years of age. Trauma andtumor causing asymmetry could be late-onset. Minortrauma to the temperomandibular joint in childhoodcould be unnoticed clinically, but gradually becomeevident.

Bimaxillary surgery involving a Le Fort Iosteotomy and bilateral sagittal split osteotomy isusually required in the surgical management of facialasymmetry. A “single-splint” surgical technique ispreferred by a number of surgeons.(39,40) The maxillo-mandibular complex is mobilized, the final occlusalsplint put on and intermaxillary fixation applied. Theposition of the maxillomandibular complex is adjust-ed intraoperatively to achieve the best aestheticresult. The predetermined ideal position may need tobe adjusted to compensate for soft tissue deformities,especially in patients with hemifacial microsomia.Intraoperative use of a face bow facilitates the posi-tioning of the maxillomandibular complex in themidline.(41)

Surgical planning of two-jaw orthognathicsurgery requires 3-dimensional consideration in thesagittal, coronal and horizontal planes. Ideally, thedental midline and skeletal midline are aligned to thefacial midline. The intercommissural plane should beparallel to the inter exocanthal plane.(40) Altug-Atac etal stated that there is no 1:1 relationship between thechanges in ramus height and improvement in paral-lelism of lip commissures to the orbital plane.(42) Thereason why it is difficult to predict the lip positionafter orthognathic surgery seems to be that soft-tissuechanges in the upper and lower lips after orthognath-ic surgery occur because of movement of the under-lying hard tissue, continuity of the orbicularis oris

muscle, and soft-tissue tension. The degree of softtissue movement as a response to skeletal structuremobilization may be difficult to predict accurate-ly.(6,43,44)

Orthognathic surgery can be combined withbone contouring such as a mandibular angle reduc-tion, mandibular inferior border ostectomy, genio-plasty, and bony augmentation as well as soft tissuecontouring such as buccal fat pad and masseter mus-cle reduction in the same operation. Minor touch-upprocedures, e.g. fat graft injection or subcutaneousliposuction, can be performed as secondary proce-dures, depending on the requirements (Fig. 4). Choiet al reported on bimaxillary orthognathic surgerycombined with a face lift procedure plus the use of aresorbable fixation device.(45) Ferguson described thedefinitive surgical correction of hemimandibularhyperplasia with complete mobilization of the inferi-or alveolar nerve bundle.(46) Anghinoni et al describedthe use of a midline mandibular osteotomy to modifythe transverse mandibular arch in the management ofmandibular asymmetry.(47)

Multiplanar distraction osteogenesis has beenapplied in the craniofacial region and this techniqueis used to correct mandibular hypoplasia. Precise andpredictable results with distraction osteogenesisrequire accurate placement of an osteotomy or cor-ticotomy, distraction device placement, vector plan-ning, and selection of a distractor as well as consid-eration of the effects of the masticatory muscles andsurrounding soft tissues that may deviate the toothbearing segment toward an unexpected position.McCarthy et al reported that only a single osteotomyand two pin sites are required in the execution ofmultiplanar distraction osteogenesis.(48) It has beenproved that distraction for lengthening the mandibu-lar ramus also increases the soft tissue by increasingthe volume of the medial pterygoid muscle, and thismay somewhat improve the facial symmetry inpatients with hemifacial microsomia.(49) Ko et al doc-umented increased length of the mandibular ramusafter one year with improvement of chin and oralcommissure positions.(50)

SummaryWhen patients complain of facial asymmetry

and seek treatment, it is important to search forunderlying causes. This entails a thorough history,physical examination, and imaging studies. An



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orthodontic consultation is required if there are den-tal and occlusal problems. Skeletal, dental and softtissue components contributing to facial asymmetryshould be carefully evaluated. The patient’s percep-tion of facial asymmetry and expectations abouttreatment results should be assessed. Inappropriateperceptions and expectations may become a con-traindication for treatment. Surgical treatment plan-ning may include staged procedures. The first stagecomprises orthognathic surgery, facial bone contour-ing surgery, genioplasty, and contouring of soft tis-sues such as the masseter muscle and buccal fat pads.If a second stage operation is required for adjustmentof the symmetry, alloplastic implants and fat injec-tion for volume augmentation, as well as bone less-ening and liposuction for volume reduction, can bedone.

AcknowledgementsThe 3-dimensional image study was supported

by a grant, CMRPG381601, from Chang GungMemorial Hospital.

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