CC
A 28-year-old female complains about her nose shape and chin appearance. She explains, “My chin has a little deviation to the right side, and I have a receding chin. Besides, I don’t like the shape of my nose.”
HPI
The patient stated that she has not been happy with the shape of her nose and the appearance of her chin, especially on profile view, because of retrogenia. In addition, she thinks that these items have decreased her beauty.
PMHX/PDHX/medications/allergies/SH/FH
Noncontributory.
Examination
General. The patient is a well-developed and well-nourished female in no apparent distress.
Psychiatric. The patient is in a fine and acceptable mood. Facial appearance is important to psychological well-being and social acceptance, and physical attractiveness may play a critical role in the development of an individual’s self-concept or even career goals (e.g., modeling). It is important to assess the patient’s motives and expectations for the surgery. Modern surgical interventions can safely enhance physical appearance, which in turn elevates self-confidence and personal well-being.
Maxillofacial. Chin deformities can manifest in any of the three dimensions (vertical, horizontal, and transverse) in isolation or in combination; however, the vast majority are in the horizontal plane only. Therefore, evaluation of the chin in three dimensions is necessary for proper diagnosis and genioplasty treatment planning. A wide range of factors can cause chin asymmetry, such as developmental, pathological, traumatic, and functional factors.
Although genioplasty is one of the safest interventions in orthognathic surgery, careful scrutiny of the skeletal, dental, and soft tissue structures is required to obtain a good result.
On the frontal view ( eFig. 90.1 ), the patient exhibits an asymmetric face with chin deviation to the right side. The patient does not have tooth show at rest. Chin pad tissue thickness is 9 mm (normal, 8–11 mm). On smiling, the lower lip is symmetrical. On elevation of the lower lip, there is no mentalis muscle hyperactivity or chin pad fasciculations. (If alloplastic augmentation is to be used, muscle hyperactivity may place excessive force on the implant, leading to increased bone resorption or displacement of the implant [ eFigs. 90.2 and 90.3 ]).
On profile examination ( Fig. 90.4 ), the patient exhibits good nasal projection with a mild dorsal hump. (A large nose makes the chin look small and vice versa.) The labiomental angle is 143 degrees. (Ideally, the depth of the fold or sulcus should lie 4 mm posterior to a line drawn from the lower vermilion border to the pogonion. If the sulcus is shallow or high, augmentation results in enlargement of the lower face [chin and lip]; however, if the fold is deep and more inferiorly positioned, augmentation predominantly accentuates the chin.) The patient demonstrates a convex facial profile with a retrognathic appearance. The cervicomental angle is obtuse at 125 degrees (normal, 110–120 degrees).
Intraoral. The patient’s oral hygiene is good. (Some clinicians will not place an alloplastic implant in patients with active periodontal disease. Also, this may be an indicator of the patient’s ability to keep the wound clean if an intraoral approach is to be used.) The patient has a class I molar and canine relationship. (A class II malocclusion indicates that a skeletal abnormality exists; the patient should be informed of the option of orthodontic realignment and orthognathic surgery.) The mandibular anterior teeth are in good position, neither retroclined nor proclined.
Imaging
Standard photographs of the frontal and profile views, both in repose and on smiling, are recommended. A panoramic radiograph and a lateral cephalogram are recommended for the workup of patients requiring a genioplasty.
The panoramic radiograph is used to delineate the proximity of the mandibular canal and mental foramen and the apices of the mandibular anterior dentition in anticipation of a genial osteotomy. In addition, it provides a general overview of any mandibular osseous pathology.
Lateral cephalometric evaluations have been used to help determine the desired horizontal and vertical dimensions of the chin. Information gained from the cephalometric tracings includes the relationship of the maxilla and mandible to the skull base and to each other. It is important to identify any skeletal or occlusal disparities that can be corrected before or concomitant with a genioplasty procedure. Ideally, the chin (the soft tissue pogonion) should rest slightly posterior to the lower lip, and the lower lip should be posterior to the upper lip. Increasing sagittal projection beyond these relations may risk an unesthetic result.
The lateral cephalogram for the current patient demonstrates the deficiency of the chin in the anteroposterior (AP) dimension (retrognathic appearance ) and a class I molar relationship ( Fig. 90.5 ).
Cone-beam computed tomography facilitates appreciation of the three-dimensional (3D) anatomy of the mandible and preoperative planning.
Labs
No routine laboratory testing is indicated for genioplasty procedures unless dictated by the medical history. The current patient reports normal medical history and routine laboratory tests before the surgery were normal.
Assessment
Retrogenia and facial asymmetry caused by chin deviation in a patient who desires chin augmentation.
Treatment
Genioplasty refers to a horizontal osteotomy of the anterior mandible as a facial cosmetic surgery procedure. It is a surgical procedure used to enhance the shape and appearance of the chin. The procedure could be either isolated or in combination with other facial cosmetic procedures such as rhinoplasty. The most common methods of genioplasty include osteotomy of the chin (also known as osseous genioplasty) and implant placement. Chin implant refers to either an alloplastic or autogenous implant. Osseous genioplasty is more versatile than alloplastic implants in improving 3D chin position. It can be used to manage vertical and AP excess or deficiency and correct midline asymmetries. Injection of dermal fillers can also be considered as a temporary method of correcting mild to moderate chin retrusion and resorption.
There are various osteotomy designs in augmentation genioplasty techniques such as sliding genioplasty, sagittal genioplasty, 3D printing genioplasty template system, and alloplastic genioplasty. Alloplastic chin implants and sliding genioplasty are the two currently accepted methods of chin augmentation ( Table 90.1 ).
| Osseous Genioplasty | Alloplastic Augmentation |
|---|---|
|
|
In genioplasty surgery, the soft tissue response to hard tissue movements is quite variable. In general, advancement movements horizontally tend to show 80% to 100% soft tissue response. Vertical augmentation demonstrates 80% to 90% soft tissue response. The response to reduction genioplasty is most variable and depends on the technique. Vertical reduction is predictable, but the amount of preoperative soft tissue redundancy is important.
Careful treatment planning, meticulous surgical technique, and the surgeon’s artistic sense are three important factors for successful and predictable chin surgery.
For intraoral access, it is important to plan an incision that achieves the following goals:
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Ease of wound closure, ensuring that movable mucosa, rather than attached gingiva, forms the wound margin
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Avoidance of periodontal problems after wound contraction and scar formation
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Prevention of mental or inferior alveolar nerve severance
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Ability to resuspend the mentalis muscle to prevent chin (mentalis) droop
An incision in the depth of the vestibule results in excessive scar formation and should be avoided. A U -shaped incision extending from canine to canine that leaves 10 to 15 mm of mucosa anterior to the depth of the vestibule is ideal. The mentalis muscle is incised in an oblique fashion, leaving an ample amount superiorly to allow for closure. The mentalis muscle is stripped in a subperiosteal plane, exposing the symphysis. The mental nerves are identified bilaterally, and the periosteum is freed circumferentially around the foramen. Careful dissection in this area allows the surgeon to preserve all branches of this nerve. The planned osteotomy should lie a minimum of 5 mm below the longest tooth root (usually the canine) and a minimum of 10 to 15 mm superior to the inferior border. The osteotomy should also extend 4 to 5 mm below the lowest point of the mental foramen. It should be remembered that the angle of the osteotomy can influence vertical and horizontal changes. An osteotomy that is more parallel with the occlusal plane allows a greater vector of advancement in the horizontal dimension. If vertical shortening is desired, the angle should be more acute. The midline should be marked with a bur (fissure type) to prevent postoperative iatrogenic asymmetries. The osteotomy is completed with a reciprocating saw. The orientation of this saw should remain constant to ensure a symmetrical cut through the buccal and lingual cortices to prevent interferences that may hamper the proposed movement. After the osteotomy has been completed and the fragment repositioned, it can be secured through a variety of methods, including the use of wires, prebent chin plates, or lag screws. The wound should be closed in layers; it is essential that the mentalis muscle be accurately repositioned. A pressure dressing is applied to facilitate soft tissue reattachment (supporting mentalis muscle repairment) and prevent hematoma formation.
Alloplastic augmentation can also be considered for the treatment of a genial deficiency. Alloplastic implants are limited to the correction of a vertical or transverse chin deficiency. A wide range of materials can be used. Those most commonly used include high-density polyethylene (Medpor, Porex Surgical Products Group), hard tissue replacement polymer, polyamide mesh (Supramid, S. Jackson, Inc.), polydimethyl-siloxane (Silastic, Dow Corning), and fibrillated expanded polytetrafluoroethylene (ePTFE; Gore-Tex, W.L. Gore & Associates). Before the removal of Proplast from the American market, various forms of Proplast (Vitek) was used for genial augmentation, such as Proplast I (PTFE and graphite), Proplast II (PTFE and alumina), and Proplast hydroxyapatite. Many surgeons believe that polydimethyl-siloxane (Silastic) meets most of the criteria for an ideal alloplastic implant.
Preformed implants, such as “off-the-shelf” implants, are readily available and cost-effective, although they may not be ideal for those with specific facial profile or particular facial goals.
Three-dimensional computer-aided design and computer-aided manufacture of customized-designed implants reduces the need to carve or shape stock implants during surgery. In patients undergoing genioplasty, custom implants are usually used to correct contour irregularities from previous unsuccessful attempts.
The ideal characteristics of an alloplastic implant include the following:
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Anatomic configuration that has a posterior surface that contours to the external surface of the mandible and an external implant shape that imitates the desired outcome
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Readily implantable and nonpalpable
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Margins of the implant blend onto the bony surfaces
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Easily removable
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Malleable, comfortable, and inert
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Easily modifiable by the surgeon during the procedure
Alloplastic augmentation can be performed via extraoral submental incision and intraoral incision. Placement of alloplastic implants via an extraoral submental incision can be combined with other procedures, such as rhytidectomy submental liposuction or platysmal placation. The surgeon’s experience is usually the deciding factor in whether an implant or an osteotomy is performed. It is generally accepted that mild to moderate abnormalities can be corrected with either alloplastic implantation or genioplasty. (Some clinicians recommend alloplastic augmentation for deficiencies up to 5 mm because mandibular resorption beyond an augmentation of 5 mm is a concern.) However, for severe abnormalities, sliding genioplasty should be performed. Genioplasty is a more versatile procedure because it can address abnormalities in any of the three dimensions. There is some debate on the superiority of either procedure for augmentation.
Computer-assisted osseous genioplasty involves performing the osteotomy virtually. From this a model can be fabricated and plates prebent. In addition, a surgical guide can be made to transfer the osteotomy line’s screw positions and a jig to accurately position the genial segment intraoperatively. Evaluation of the accuracy of this technique has shown that it is promising.
The application of digital design technology compared with conventional techniques can provide various benefits for both the surgeon and patient. Significant advantages that are certainly of particular importance to surgeons are more accurate and more predictable surgical outcomes and reduction in operating time.
Injectable soft tissue filler substances such as hyaluronic acid fillers can play an important role in the aesthetic treatment to improve facial areas such as the chin shape and the mandibular line and can also be selected as an alternative treatment for chin augmentation and has the advantage of simple operation and few complications. Because the skin on the chin is quite thick, contour irregularity with supraperiosteal injection is often not of particular concern.
For the current patient, computer-assisted horizontal translational osseous genioplasty, minimally invasive rhinoplasty, and septoplasty were performed simultaneously. This is a new computer-assisted genioplasty technique for the correction of chin asymmetries. Before surgery the 3D computed tomography of the lower jaw area was obtained ( Fig. 90.6 ). To accurately design the virtual chin osteotomy, raw data were input into software. Eventually, a customized module was exclusively designed for the patient deformity ( eFig. 90.7 and Fig. 90.8 ). First the patient was intubated through the nose and underwent advancement genioplasty of 7 mm, and the chin was transferred 4 mm to the left side to correct deviation using a chin osteotomy surgical guide and through computer-assisted horizontal translational osseous genioplasty ( Fig. 90.8 , eFig. 90.9 , and Fig. 90.10 ). Afterward the patient was intubated through the mouth, and septorhinoplasty was accomplished through minimally invasive rhinoplasty and dorsal preservation using piezoelectric. Computer-assisted horizontal translational osseous genioplasty is a simple and reliable technique for patients with facial asymmetry caused by chin deviation.
