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DOI: 10.1051/odfen/2013205 J Dentofacial Anom Orthod 2013;16:305� RODF / EDP Sciences

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Article received: 02-2013Accepted for publication: 03-2013

When anthropologicalconsiderations influenceour attitude about the chinand orthognathic surgery

Mohamed EL-OKEILY, Masrour MAKAREMI

ABSTRACT

The presence of a chin is a specific and unique feature of the human face thatis absent from the face of our hominid ancestors and all other primates. Anumber of anthropologists have studied this anthropomorphic characteristic andelaborated various theories concerning its genesis and anatomical usefulness.Recent research based on the analysis of stress using the finite elementmethod (FEM) seems to establish that the presence of the chin is abiomechanical consequence of skeletal and muscular equilibrium peculiar to thehuman face. This data is an important addition to our matrix of thoughts thatinfluences our attitude concerning the chin and orthognathic surgery. Inparticular, whether or not a genioplasty is necessary, and whether it should beperformed separately from orthognathic surgery or at the same time.

KEY WORDS

Genioplasty Mentoplasty

Chin Orthogathic surgery

Anthopology of the chin

INTRODUCTION

The surgical correction of facial dyspla-sias is an important and growing multidisci-plinary field today. Case management of

these dysplasias requires a treatment planthat involves close collaboration betweenthe orthodontist and the maxillofacial

Address for correspondence:

El-Okeily M.Centre Bordelaisde Chirurgie Maxillo-Faciale17, rue Esprit des Lois, 33000 [email protected] available at http://www.jdao-journal.org or http://dx.doi.org/10.1051/odfen/2013205

http://www.jdao-journal.org

http://dx.doi.org/10.1051/odfen/2013205

surgeon. This team, assisted bymany practitioners, tries to address a

two-fold objective that is both func-tional and morphological. The chinoccupies a unique and importantplace in the treatment plan both froma morphological and functional per-spective.

The chin (the trigonum mentale):whose base corresponds to the infer-ior border of the mandibule andwhose summit reaches the medianridge of the mental symphysis, differ-entiates a central mammelon: themental tubercle. The mental protu-berance is beneath a depression: themandibular curves, this protuberancecauses the bony part of the chin tojut forward.

The chin is the paleontological cri-terion of choice to differentiate amodern mandible from a more primi-tive mandible. The appearance of thechin is still a highly topical issue.

This anthropological view of thechin has provided us with a new wayof considering procedures when per-forming orthognathic surgery.

WHY DO WE HAVE A CHIN?

Different theories

The dental theory concerning themental protuberance is the result ofthe appearance and deepening of themandibular curve occurring at thejunction of the two parts of themandible: the underlying alveolar partand the underlying basal part. Theformation of the anterior mandibularcurve is made possible due to the lin-gual inclination of the roots of both

the incisors and the canines and alsobecause of the decrease in thelength of the dental arch.

According to more current theories(Groning et al.) the presence of thechin is a biomechanical consequenceof the skeletal and muscular equili-brium that is unique to the humanface. In particular, the stresses gen-erated by masticatory muscles in thecourse of lateral and vertical move-ments that take place during the

Different shapes of the chin, from the work ofGroning et al.

MOHAMED EL OKEILY ET MASROUR MAKAREMI

2 El Okeily M., Makaremi M. When anthropological considerations influence our attitude aboutthe chin and orthognathic surgery

masticatory cycles seem to play amajor role in the development of thechin.

Their conclusion comes as a resultof a series of experiments made pos-sible by implementing a powerfulmathematical model based on finiteelements and thus demonstratingthat the appearance of the chin isa logical outcome for the mandibleof anatomically modern humans

because of the distribution of stres-ses from the masticatory musclesand occlusal pressures, but also be-cause of the thinning of the skeletonof anatomically modern humans. Ad-ditionally, they demonstrated that theabsence of the chin can be justifiedby the same mathematical modelsthat justify cases of disequilibriumdue to vertical excess or exaggeratedrobustness.

GENIOPLASTY: TECHNICAL PRINCIPLES

General considerations

Many techniques are described forperforming a genioplasty. We willjust provide a description of the stan-dard technique or the current techni-que most widely used forgenioplasty.

A genioplasty can be the only sug-gested treatment or it can representone part of the treatment. It can alsobe the only surgical part of the thera-peutic treatment plan of the patientor it can be one stage in a series ofsurgical procedures.

The indication for a genioplasty canmodify the surgical technique andeven change the timeframe chosento perform it.

Treating the mental symphysis

The positioning of the patient mustbe done rigorously and must adhereto the standard practice of orthog-nathic surgery. The patient is in thehead up position to reduce bleeding.The head is stabilized in a neutral po-sition.

After an injection of Xylocaine withadrenaline also in order to reduce peri-operative bleeding, the practitioner be-gins the intraoral procedure. Theincision, in an inverted V shape ismade approximately 15 mm from thedepth of the vestibule from 33 to 43.

The incision is made through theorbicular oris muscle of the lips thentowards the periosteum that it

Constraints in all three axesConstraints in the vertical axis

b caDisplacement (mm)

0 250 500 750 1000

Stresses from pressure, from Groning et al.

WHEN ANTHROPOLOGICAL CONSIDERATIONS INFLUENCE OUR ATTITUDE ABOUT THE CHIN AND ORTHOGNATHIC SURGERY

Rev Orthop Dento Faciale 2013;16:305. 3

pierces until stopped by osseouscontact.

Next, the surgeon retracts a widesection of the symphysis thus makingit possible to locate the mental nervesand to stop at the basal border.

Osteotomy

Marking the incision site as de-scribed by Obwegeser in 1957 is stillwidely used.

The shape, thickness and type ofosteotomy will depend entirely onthe indication.

The osteotomy must maintain asafe distance of at least five milli-meters from the dental roots andfrom the mental nerves.

The incision site is marked with around bur and/or piezoelectric deviceand then completed by using a reci-procating saw or a round bur with alarger diameter.

The angle of the osteotomy is par-ticularly important since it will have adirect impact on the height of thelower third of the face.

The angle can be horizontal or obli-que downwards and backwards. Itcan be single or multiple.

Movements

Various types of movements arepossible once the symphysis hasbeen freed and is mobile.

An advancement or forward slidinggenioplasty, genioplasty for verticallengthening or elongation, genioplastyfor reduction (an intermediary bonefragment is removed) or impaction are

all possibilities offered by this techni-que. We should also mention the‘‘tenon and mortise’’ genioplasty in-volving a central osseous plate thatguides the advancement. There is alsothe ‘‘jumping’’ genioplasty or overlap-ping, that consists in completely mov-ing the fragment forward from theremaining symphysis.

A recent variation described byTriaca A. called ‘‘chin wing’’, allowsthe surgeon to detach the chin fromthe lower border of the mandible(from the angle of the mandible onone side to the angle of the mandibleon the other side) and makes it pos-sible to additionally modify the posi-tion of the chin, to assess(independently from the movementof the dental portion of the mandiblethat is performed at the same timeas a standard mandibular osteotomy)the relief of the line separating theface from the neck. This allows thepractitioner to more accurately moni-tor the shape, the height and thewidth of the face.

Attaching and closing

Anchorage with steel wires, hasbeen replaced more and more withrigid fixation for osteosynthesis thatuses miniplates or compressionscrews. The preformed and pre-mea-sured miniplates that are in a ‘‘crabshape’’ are currently used most ofthe time.

Next, the closing is achieved intwo planes using absorbable suturesfor muscle reinsertion that has to beperformed with particular care.

A compression bandage is kept inplace from 24 to 72 hours.



Other techniques andsupplemental procedures

Some supplemental proceduresare possible and regularly implemen-ted:– Procedures for periodontal care:

treatment for muscular fragilitydue to reinsertion of the musclesin a more inferior position on thebulbous portion of the chin. Somemucosal and/or gingivoplasties.

– Bone grafts: placed for the purposeof reinforcing incisor periradicularprotection.

Other techniques have been usedbut they are still provisional:– Chin prostheses: they are techni-

cally easier to use and presentminor short-term side effects. How-ever, they are often a source ofinfection, of secondary movementor osseous erosion in the long term.

– The cutaneous approach: may al-low the practitioner to make smallcartilaginous and/or bone graftswhose long term reliability andstability remain questionable.

– Bone abrasion: it used to be widelyperformed, but is now increasingly

Geoffrey’s case



associated with ‘‘witch’s chin’’ thatis linked to muscular fat ptosis. Thisprocedure is used only for limitedand specific remodeling.

Side effects and complications

In general, the side effects ofgenioplasty are rather minor. After a24 hour stay in the hospital, the dis-comfort is the result of localizededema and especially labio-mentalnumbness that can last severalmonths.

The main complications are shortterm bleeding (rarely requiring drai-nage), secondary movement (veryrare since the development of rigidfixation osteosynthesis) and bone re-sorption in cases of ‘‘jumping’’ orbone grafts.

However, there is no such thing asa ‘‘simple’’ surgical procedure, andthe rare serious complications (hema-

toma of the buccal floor, respiratoryproblems, etc.) make it essential tocarefully consider the indications andthe possible alternatives.

The period of patient adjustment tothe esthetic modification generally re-quires more time than expected andin this case, considerable preliminarypreparation.

The main ‘‘complication’’, if it cantruly be considered a complication, isthe postoperative dissatisfaction withthe result of the procedure: undercor-rection, overcorrection, inadequatecorrection. . .

Often, the recognition of this ‘‘im-perfection’’ is delayed and can takeplace six months after the procedure.This is why we consider the indica-tion for a genioplasty, as well as thetiming of the procedure to be essen-tial for determining an optimal treat-ment plan for the patient.

INDICATIONS

From the very beginning of casemanagement, we have to take intoconsideration the possible need foran additional surgical procedure forthe chin.

The practitioner must have a dualperspective that includes both mor-phology and function.

The morphological perspective issubjective and the esthetic or stan-dard cephalometric norms should beused with caution. There is certainlya place for a minor receded chin on afemale face that can be charmingjust as a slightly receded chin can ap-pear unsuited for some male faces.

Therefore, we think that these normscan serve as a rough and basic fra-mework for determining treatmentand must be adapted case by case.What patients feel and what they ex-pect are, in this case, fundamentaland one of the difficulties will be todetermine as precisely as possiblethe expectations of the patients andtheir own capacity to adjust to thechange in their appearance.

As for the functional perspective, itincludes a number of parameters:– labial ‘‘competence’’ at rest and in

motion with the occlusal compo-nent (on one hand maxillary and on



the other mandibular) and the men-talis component.

– nasal or mouth breathing withpossible obstacles to nasal breath-ing (cartilaginous and osseous nasalblockage, polyps, tonsils. . .)

– The tongue position at rest or inmotion (swallowing inter alia), thevolume and morphology of thetongue and the space available forthe tongue.

– Mentalis musculature at rest and inmotion.

– The possible presence of sleepapnea syndrome.

– The overall posture of the body andin particular a possible cervicalprotrusion.

– Labial tone and labial volume.By using this dual morphological

and functional perspective, the practi-tioner can immediately divide thepatients into two separate groups:– A ‘‘caricature’’ group whose indica-

tion for a genioplasty is immediatelyevident

– An ‘‘uncertain’’ group for whom itdifficult to know in advance if themorphological and functional re-sults will be inadequate and if their

In these 2 cases where a genioplasty was initially considered advisable, the choice todelay the decision for 8 months made it possible to more accurately determine the

indication.

Natacha’s case: no need for a genioplasty,. . .

. . .Nathalie’s case: performing a genioplasty more suitably adapted to the patient.



condition will not be completelyresolved by a treatment plan ‘‘with-out a genioplasty’’Given the number of parameters

involved, the multitude of treatmentplans that could be started (maxillaryimpaction, labioplasties, lingual re-training, improving nasal breathing,etc.) and the impossibility of predict-ing how the patient will respond to

these treatments, we think it wouldbe wise to defer the genioplasty pro-cedure until after orthognathic sur-gery has taken place.

Even in cases where this procedureturns out to be necessary, the plan-ning and the performing of the genio-plasty as well as the results will bemore accurate and more satisfying.

DISCUSSION

The matrix of this study takes intoaccount the functional chin that isspecific to humans.– To the extent that the orthognathic

surgery can restore this function:

we provide the face with theopportunity ‘‘to create its own chin’’

– If the functional context is obviouslyunfavorable: mentoplasty shouldimmediately be planned.

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