In contemporary orthognathic surgery planning, the genium/chin constitutes an important part that contributes to the maxillofacial profile. The aesthetics of the lower face is affected by the position of the genium which makes reestablishment of genial morphology an essential component. It is hence necessary to evaluate the genium objectively on its individual merit, and any discrepancy is addressed accordingly. This review presents an overview of contemporary genioplasty techniques, their applications, and considerations on stability, osteosynthesis, complications, and the future developments.
Key points
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Genioplasty is a versatile procedure and is applicable to various case scenarios.
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The technique was described for over 7 decades and evolved with numerous technical modifications.
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Three-dimensional (3D) clinical and cephalometric assessment of the genium relative to the face is an important prerequisite.
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Preoperative planning can be aided by simulation and 3D models to enable fabrication of cutting guides and patient-specific implants to enhance precision.
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Genioplasty is proved to be a standard procedure to address functional issues.
Introduction
Facial profile is perceived to be associated with attractiveness and intelligence. Among the various attributes that render balance to a face, the genium/chin constitutes an important part that contributes to the facial profiles. The aesthetics of the lower face is greatly determined by the genium, , which makes reestablishment of the genial morphology vital in corrective facial surgery. It is hence necessary to evaluate the genium objectively on its individual merit, and any discrepancy is addressed accordingly.
Historically, surgical intervention to correct deformities of the genium was carried out only in cases of retrogenia, wherein autograft placement was facilitated through an extraoral submental incision. , Aufricht and colleagues performed a genial augmentation using osseocartilaginous tissue obtained from reduction of a dorsal nasal hump. The first surgical procedure performed to correct a genial deformity was an advancement genioplasty. Hofer proposed an extraoral approach for a horizontal symphyseal osteotomy in cadavers. Gillies and Millard replicated Hofer’s technique in vivo. , Obwegeser revolutionized the surgery through an intraoral approach. This was performed to correct a retruded chin in a patient with satisfactory dental occlusion, with the aim to minimize resorption and to facilitate contact healing by retaining good bony approximation. Reichenbach and colleagues described an intrusive/impaction genioplasty to bring forth a vertical reduction in genial height through a superior rotation of the lower segment after a wedge ostectomy. Converse and Smith published a technique to increase the vertical genial height with interposition of an autograft. Genial tapering and shaping to enhance aesthetics and feminization were reported by Ousterhout. Distraction osteogenesis to widen the mental region was also reported. , Genioplasty is also indicated to improve lip competency and widening the tongue space for airway improvement in patients with obstructive sleep apnea.
This review aims to present an overview of contemporary genioplasty techniques, their applications, and considerations on stability, osteosynthesis, complications, and the future developments.
Assessing a patient for genioplasty
Assessment of the chin should include symmetry, vertical dimension and width relative to the overall shape of the face, and the presence of canting involving the inferior border of mandible. Tide and colleagues proposed a concept of Quick Analysis of the Chin, which included parameters such as (i) lip eversion (due to microgenia and deep overbite), (ii) mandibular anterior teeth evaluation and thickness of chin pad (8–11 mm on an average), (iii) depth and height of the labiomental fold, and (iv) dynamic chin pad motion while smiling. A few important clinical assessments and reference lines are described in Table 1 .
| Assessment Parameters | Definition |
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| E line (Ricketts, 1954) | Measured from pronasale to pogonion; depicts lip position relative to chin and nose (line should cross 2 mm and 4 mm from lower and upper lips, respectively) |
| S line (Steiner, 1953) | Subnasale to pronasale to soft tissue pogonion; for lip prominence evaluation (0 ± 2 mm from both upper and lower lips) |
| Legan’s angle (Legan and Burstone, 1980) | Angle formed from lines through glabella to subnasale and subnasale to pogonion; angle of facial convexity (8°–16°, average of 12°) |
| Zero Meridian (Gonzalles-Ulloa, 1968) | Perpendicular line to Frankfurt’s plane through nasion; pogonion should coincide with line or be slightly (0 ± 2 mm) behind line, subnasale 8 mm behind to line |
| Cervicomental angle | Angle between two tangents. First tangent to the neck at sub-cervical junction (lowest point of submental and neck area juncture) and second tangent to submental area (genium to sub-cervical area); normal values in females is 126° and in males is 121° |
| Riedel line | Associates the most prominent spots on the lower and upper lips with the protuberant point on the genium |
| Byrd analysis line | Tangent to the upper lip drawn from mid-dorsal region of nose up to chin. Genium should ideally be 3 mm behind the above tangent |
Role of Genioplasty in Contemporary Orthognathic Surgery
The contemporary principles of orthognathic surgery address the cosmetic as well as functional requirements of a patient with skeletal deformity. The osteotomy design and vector of bony movement are determined by the plane in which correction is required. Hence, a thorough understanding of the deformity in all planes is required to arrive at an accurate diagnosis and to establish a pertinent treatment plan.
Genioplasty for correcting sagittal (anteroposterior) deformities
Alloplastic implants are commonly used for addressing an anteroposterior genial deficiency. This provides satisfactory results in cases with discrepancies of 4 to 5 mm. However, larger corrections may represent a substantial underlying orthognathic deformity and mandate planning to include osseous genioplasties with or without surgery of the maxilla or mandible. Osseous genioplasty also demonstrates better soft tissue contours in comparison with alloplastic implants. Augmentation of the genium with silicone, , porous polyethylene (Medpore), expanded polytetrafluoroethylene , , (currently not used), hydroxyapatite, and mersilene , has been described in the literature. To prevent dislodgement of the implants, fixation is usually necessary. Although healing after alloplast placement is faster than osseous genioplasty, it is not suitable for three-dimensional (3D) correction of moderate-to-severe genial deformities. Infection, graft rejection, resorption, extrusion, contraction, and lower lip retraction are the documented complications with alloplasts. However, studies that compared alloplastic implants with osseous genioplasty reported no significant resorption or infection of the alloplast in long term. The use of autograft, allogenic bone graft, and fat grafting for chin contour correction has also been described but with limited success. Table 2 summarizes the various alloplastic materials and their advantages and disadvantages.
| Material | Advantages | Potential Disadvantages |
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| Silicone (dimethylpolysiloxane) |
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Bone erosion, excessive fibrosis, foreign body reaction, implant migration, fragmentation infection, and button chin appearance |
| Acrylic (methylmethacrylate) |
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Brittle, palpable, resorptive effects, and exothermic during setting |
| Medpore (porous polyethylene) |
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May induce granulomatous reactions Requires good soft tissue coverage (compromised in thin skin areas) |
| Polyamide mesh (organopolymer related to nylon, Supramid) |
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Fragmentation, resorption, foreign body reaction due to black carbon particles, and degradation by hydrolysis—resulting in progressive bulk loss every year , |
| Hard tissue replacement: polymethylmethacrylate merged with poly-2-hydroxyethylmethacrylate coated with calcium hydroxide |
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Lack of osteoinductive properties |
| Gore-Tex (expanded polytetrafluoroethylene) |
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Severe bone erosion/resorption |
| Proplast I (with carbon fibers), Proplast II (with aluminum oxide), Proplast hydroxyapatite (HA) |
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Questionable long-term stability, multinucleate giant cell reaction |
| HA |
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Rigidity, needs good soft tissue cover, hard to shape, difficult to fix, decreased shear resistance, brittle (porous type) |
| Mersilene (polyester fiber) |
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Genioplasty allows the chin to be advanced ( Figs. 1 and 2 ) or setback ( Figs. 3 and 4 ) in the anteroposterior plane. The indications for anteroposterior correction include (1) retruded/protruded genium, (2) lower third deformity, (3) management of obstructive sleep apnea, and (4) as an adjunct to cosmetic procedures such as rhinoplasty and facelifts. Until the 1950s, setback of the chin was the only practiced technique. With the advent of contemporary methods of planning, the role of osseous genioplasty has expanded significantly.
In a clinical situation that requires pure anteroposterior movement, care is taken to ensure a horizontal osteotomy design in the sagittal plane with minimal oblique angulation ( Fig. 5 ). This ensures an optimal movement without any unplanned change in the vertical dimension. , In case of a combined vertical deformity, the osteotomy design may be modified to incorporate an angulation, , which depends on the vertical change required. Movement along a true horizontal vector would minimally increase the genial height, whereas reduction of the genial height could be achieved using a steep oblique vector of movement. Advancement or setback of the genium may produce bony protuberances/steps at the junction between osteotomized segment and the mandibular corpus. This needs to be adjusted to achieve a smooth jawline and soft tissue contour. , , When extreme advancements of 10 mm to 14 mm are required, interpositional grafts may be placed as required.
Genioplasty for correcting vertical (supero-inferior) deformities
Management of vertical discrepancies may be performed to increase or reduce the lower facial height. The correction of mild discrepancies in the vertical dimension can be achieved by modifying the vector of movement in the sagittal plane and the osteotomy design as previously described (see Fig. 5 ). However, true changes to the vertical dimension may be achieved by exclusively down-grafting or impacting the chin after osteotomy.
To increase vertical dimension of the chin, an osteotomy is performed to mobilize the genial segment which is then down-grafted and fixed at the preplanned position. A bone graft is interposed to allow bone contact and improve stability ( Fig. 6 ). The placement of the graft should be passive to prevent any inadvertent change of the position.
To reduce chin height, two horizontal osteotomy cuts are performed to remove a predetermined amount of intervening bone ( Figs. 7 and 8 ). Care is taken to avoid damage to the root apices. Modifications can be incorporated in the osteotomy design to produce forward or backward rotation of the genial tip. Removal of a bone segment that is wider anteriorly would produce anterior rotation of the genial tip, whereas bone removal that is wider posteriorly rotates the tip posteriorly. If the genium seems redundant, as is the case with most patients with vertical excess, a minimal advancement of the genium can be performed to balance the soft tissue profile.
Genioplasty for correcting transverse (mediolateral) deformities
The chin can be narrowed or widened to correct any transverse deformities ( Fig. 9 ). Genioplasty for narrowing is a more commonly performed procedure which facilitates a sharp and triangulated appearance of the chin. The osteotomies can also be tailored to address anterior and posterior component deformities.
