DOI: 10.1051/odfen/2013205 J Dentofacial Anom Orthod 2013;16:305 Ó RODF / EDP Sciences When anthropological considerations influence our attitude about the chin and orthognathic surgery Mohamed EL-OKEILY, Masrour MAKAREMI ABSTRACT The presence of a chin is a specific and unique feature of the human face that is absent from the face of our hominid ancestors and all other primates. A number of anthropologists have studied this anthropomorphic characteristic and elaborated various theories concerning its genesis and anatomical usefulness. Recent research based on the analysis of stress using the finite element method (FEM) seems to establish that the presence of the chin is a biomechanical consequence of skeletal and muscular equilibrium peculiar to the human face. This data is an important addition to our matrix of thoughts that influences our attitude concerning the chin and orthognathic surgery. In particular, whether or not a genioplasty is necessary, and whether it should be performed 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- these dysplasias requires a treatment plan sias is an important and growing multidisci- that involves close collaboration between plinary field today. Case management of the orthodontist and the maxillofacial Address for correspondence: Article received: 02-2013 El-Okeily M. Accepted for publication: 03-2013 Centre Bordelais 1 de Chirurgie Maxillo-Faciale 17, rue Esprit des Lois, 33000 Bordeaux [email protected] Article available at http://www.jdao-journal.org or http://dx.doi.org/10.1051/odfen/2013205 MOHAMED EL OKEILY ET MASROUR MAKAREMI two-fold objective that is both func- tional and morphological. The chin occupies a unique and important place in the treatment plan both from a morphological and functional per- spective. The chin (the trigonum mentale): whose base corresponds to the infer- ior border of the mandibule and whose summit reaches the median ridge of the mental symphysis, differ- entiates a central mammelon: the mental tubercle. The mental protu- berance is beneath a depression: the mandibular curves, this protuberance causes the bony part of the chin to jut forward. The chin is the paleontological cri- terion of choice to differentiate a modern mandible from a more primi- tive mandible. The appearance of the Different shapes of the chin, from the work of chin is still a highly topical issue. Gro¨ ning et al. This anthropological view of the chin has provided us with a new way surgeon. This team, assisted by of considering procedures when per- many practitioners, tries to address a forming orthognathic surgery. WHY DO WE HAVE A CHIN? Different theories the incisors and the canines and also because of the decrease in the The dental theory concerning the length of the dental arch. mental protuberance is the result of According to more current theories the appearance and deepening of the (Gro¨ ning et al.) the presence of the mandibular curve occurring at the chin is a biomechanical consequence junction of the two parts of the of the skeletal and muscular equili- mandible: the underlying alveolar part brium that is unique to the human and the underlying basal part. The face. In particular, the stresses gen- formation of the anterior mandibular erated by masticatory muscles in the curve is made possible due to the lin- course of lateral and vertical move- gual inclination of the roots of both ments that take place during the 2 El Okeily M., Makaremi M. When anthropological considerations influence our attitude about the chin and orthognathic surgery WHEN ANTHROPOLOGICAL CONSIDERATIONS INFLUENCE OUR ATTITUDE ABOUT THE CHIN AND ORTHOGNATHIC SURGERY Constraints in all three axes Constraints in the vertical axis a bc Displacement (mm) 0 250 500 750 1000 Stresses from pressure, from Gro¨ ning et al. masticatory cycles seem to play a because of the distribution of stres- major role in the development of the ses from the masticatory muscles chin. and occlusal pressures, but also be- Their conclusion comes as a result cause of the thinning of the skeleton of a series of experiments made pos- of anatomically modern humans. Ad- sible by implementing a powerful ditionally, they demonstrated that the mathematical model based on finite absence of the chin can be justified elements and thus demonstrating by the same mathematical models that the appearance of the chin is that justify cases of disequilibrium a logical outcome for the mandible due to vertical excess or exaggerated of anatomically modern humans robustness. GENIOPLASTY: TECHNICAL PRINCIPLES General considerations Treating the mental symphysis Many techniques are described for The positioning of the patient must performing a genioplasty. We will be done rigorously and must adhere just provide a description of the stan- to the standard practice of orthog- dard technique or the current techni- nathic surgery. The patient is in the que most widely used for head up position to reduce bleeding. genioplasty. The head is stabilized in a neutral po- A genioplasty can be the only sug- sition. gested treatment or it can represent After an injection of Xylocaine with one part of the treatment. It can also adrenaline also in order to reduce peri- be the only surgical part of the thera- operative bleeding, the practitioner be- peutic treatment plan of the patient gins the intraoral procedure. The or it can be one stage in a series of incision, in an inverted V shape is surgical procedures. made approximately 15 mm from the The indication for a genioplasty can depth of the vestibule from 33 to 43. modify the surgical technique and The incision is made through the even change the timeframe chosen orbicular oris muscle of the lips then to perform it. towards the periosteum that it Rev Orthop Dento Faciale 2013;16:305. 3 MOHAMED EL OKEILY ET MASROUR MAKAREMI pierces until stopped by osseous all possibilities offered by this techni- contact. que. We should also mention the Next, the surgeon retracts a wide ‘‘tenon and mortise’’ genioplasty in- section of the symphysis thus making volving a central osseous plate that it possible to locate the mental nerves guides the advancement. There is also and to stop at the basal border. the ‘‘jumping’’ genioplasty or overlap- ping, that consists in completely mov- ing the fragment forward from the remaining symphysis. Osteotomy A recent variation described by Marking the incision site as de- Triaca A. called ‘‘chin wing’’, allows scribed by Obwegeser in 1957 is still the surgeon to detach the chin from widely used. the lower border of the mandible The shape, thickness and type of (from the angle of the mandible on osteotomy will depend entirely on one side to the angle of the mandible the indication. on the other side) and makes it pos- sible to additionally modify the posi- The osteotomy must maintain a tion of the chin, to assess safe distance of at least five milli- (independently from the movement meters from the dental roots and of the dental portion of the mandible from the mental nerves. that is performed at the same time The incision site is marked with a as a standard mandibular osteotomy) round bur and/or piezoelectric device the relief of the line separating the and then completed by using a reci- face from the neck. This allows the procating saw or a round bur with a practitioner to more accurately moni- larger diameter. tor the shape, the height and the The angle of the osteotomy is par- width of the face. ticularly important since it will have a direct impact on the height of the lower third of the face. Attaching and closing The angle can be horizontal or obli- que downwards and backwards. It Anchorage with steel wires, has can be single or multiple. been replaced more and more with rigid fixation for osteosynthesis that uses miniplates or compression Movements screws. The preformed and pre-mea- sured miniplates that are in a ‘‘crab Various types of movements are shape’’ are currently used most of possible once the symphysis has the time. been freed and is mobile. Next, the closing is achieved in An advancement or forward sliding two planes using absorbable sutures genioplasty, genioplasty for vertical for muscle reinsertion that has to be lengthening or elongation, genioplasty performed with particular care. for reduction (an intermediary bone A compression bandage is kept in fragment is removed) or impaction are place from 24 to 72 hours. 4 El Okeily M., Makaremi M. When anthropological considerations influence our attitude about the chin and orthognathic surgery WHEN ANTHROPOLOGICAL CONSIDERATIONS INFLUENCE OUR ATTITUDE ABOUT THE CHIN AND ORTHOGNATHIC SURGERY Other techniques and Other techniques have been used supplemental procedures but they are still provisional: – Chin prostheses: they are techni- Some supplemental procedures cally easier to use and present are possible and regularly implemen- minor short-term side effects. How- ted: ever, they are often a source of – Procedures for periodontal care: infection, of secondary movement treatment for muscular fragility or osseous erosion in the long term. due to reinsertion of the muscles – The cutaneous approach: may al- in a more inferior position on the low the practitioner to make small bulbous portion of the chin. Some cartilaginous and/or bone grafts mucosal and/or gingivoplasties. whose long term reliability and – Bone grafts: placed for the purpose stability remain questionable. of reinforcing incisor periradicular – Bone abrasion: it used to be widely protection. performed, but is now increasingly Geoffrey’s case Rev Orthop Dento Faciale 2013;16:305. 5 MOHAMED EL OKEILY ET MASROUR MAKAREMI associated with ‘‘witch’s chin’’ that toma of the buccal floor, respiratory is linked to muscular fat ptosis.