Patients with small lower jaws may derive aesthetic

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1 Operative Strategies Enlarging the Deficient Mandible Michael J. Yaremchuk, MD; Yi-Chieh Chen, MD Dr. Yaremchuk is Clinical Professor of Surgery, Harvard Medical School and Chief of Craniofacial Surgery, Massachusetts General Hospital, Boston, MA. Dr. Chen is from the Department of Plastic Surgery, Chang-Gung Memorial Hospital, Chang-Gung University, Taipei, Taiwan. The authors describe a technique to improve skeletal contours of the deficient mandible with normal occlusion using alloplastic implants, often in combination with chin lengthening or shortening. Successful outcomes depend on knowledge of normal facial skeletal relationships, appropriately designed biocompatible implants, and facility with craniofacial techniques. (Aesthetic Surg J 2007;27: ) Patients with small lower jaws may derive aesthetic benefit from alloplastic augmentation of both the anterior and posterior mandible. Augmenting the contours of the mandible balances facial dimensions, while adding definition and angularity to the lower third of the face. Most patients with small mandibles have a normal occlusion. Significant mandibular deficiency may result in Class II dental malocclusion. While most of these patients can have their dental relationships normalized through orthodontic tooth movement, those with severe mandibular deficiency require surgical advancement of the mandible to correct the malocclusion. The classic method of correcting Class II dental malocclusion (in patients with significant mandibular deficiency), includes sagittal split ramus osteotomy, sliding advancement genioplasty with possible LeFort I maxillary impaction, and preoperative and postoperative orthodontic treatment. This combination of procedures can provide a Class I dental relationship and normalize the skeletal contour. In patients with mandibular deficiency who have had malocclusion corrected through orthodontics alone, mandibular osteotomy would disturb the dental relationships, requiring the patient to undergo extensive perioperative orthodontic treatment. This type of treatment is both costly and time-consuming. Alloplastic augmentation of the mandible can provide a visual effect similar to, and, in our opinion, superior to that of sagittal osteotomy with advancement. 1 The technique described here improves the skeletal contours of the deficient mandible with normal occlusion. The anatomy associated with a deficient mandible that can be camouflaged with implants includes the obtuse mandible angle with steep mentocervical angle, decreased vertical and transverse ramus dimensions, and a poorly projecting chin. When the chin is deficient in both the vertical and sagittal dimensions, it is lengthened vertically by horizontal osteotomy and augmented sagittally with an implant. When the poorly projecting chin is long in the vertical direction, it is shortened and then augmented sagittally with an implant. In addition to normalizing the dimensions of a deficient mandible, modest augmentation of the lower jaw with normal dimensions can help balance upper and lower facial relationships and increase angularity. Evaluation and Planning Physical examination Physical examination is the most important element in preoperative assessment and planning. Reviewing the patient s life-size frontal and lateral photographs together with the patient can be helpful when discussing aesthetic concerns and goals. To allow the patient to understand the scale and scope of augmentation, it is useful to have sample implants with which to demonstrate placement in a model skull and to apply directly to the appropriate area of the patient s face. All faces are asymmetric. Asymmetries are usually subtle but, with sufficient scrutiny, detectable. Their recognition, before surgery, is important to both the surgeon and the patient. Asymmetry should be pointed out during the preoperative consultation so that the patient can anticipate this in the postoperative result. Aesthetic Surgery Journal ~ September/October

2 X-rays Posteroanterior and lateral cephalograms may be used to provide data that can help determine how best to alter implant dimensions to suit each patient. Three-dimensional computerized tomographic scans and the models obtained from their data can be invaluable in attempting to correct asymmetries associated with congenital, posttraumatic, or postsurgical deformities. However, most procedures are performed without preoperative radiology assessment. In general, the size and position of the implants are largely aesthetic judgments. Facial measurements Because implant augmentation of the facial skeleton results in measurable changes in facial dimensions and proportions, it is intuitively appealing and appropriate to use facial measurements to evaluate the face and guide surgery. Although usually referenced in discussions of facial skeletal augmentation, neoclassical canons, based on idealization, have a limited role in surgical evaluation and planning. When facial dimensions of normal men and women were evaluated objectively and compared with those found in ideal artistic representations, it was found that some proportional relationships found in healthy, normal individuals are reflected in ideal representations, and others are never found. 2,3 Anthropometric data facilitate facial evaluation and surgical planning by describing normal facial measurements and relations. With this framework, the status of the patient is more easily understood and the goals of surgery defined. We prefer to use the anthropometric data of Farkas. 4 The dimensions and complex configuration of the face make millimeter differences and changes noticeable and significant. Implants that are too large create unnatural contours that relate poorly to other facial areas. Inappropriate implants may therefore upset facial balance. Facial implants must be appropriately sized, shaped, and positioned to be effective. Implants Most alloplastic facial skeleton augmentation is performed with implants made of silicone rubber or porous polyethylene. The senior author (M.Y.) prefers firm and flexible porous polyethylene implants (Medpor; Porex, Fairborn, GA) to augment the facial skeleton. This material is easily carved with a scalpel or contoured with a rasp or motorized burr and can be immobilized with sutures or screws, the latter being preferred. Porous polyethylene has pores of sufficient size to allow fibrous tissue ingrowth and (relative) host incorporation as compared with the host encapsulation observed with smooth-surfaced implants. Rather than the dense connective tissue capsules seen in smoothsurfaced implants, porous polyethylene implants exhibit a thin connective tissue contiguous with the ingrown tissue. 5 Use of porous implants has been criticized because, unlike smooth implants, they require wider exposure for positioning and are more difficult to remove. After negotiating the learning curve, both these problems have become insignificant for the senior author. Also, wider exposure has been demonstrated to result in more accurate implant positioning. Furthermore, because initial augmentation has been perceived as accurate for most patients, revisional surgical procedures are less frequent. When porous polyethylene implants need removal, dissection directly on the implant minimizes adjacent soft tissue trauma. The manufacturer provides multiple implant shapes and sizes intended for specific anatomic areas. It is unusual to use an implant without changing its contour (reducing it) to meet the needs of a specific patient. Ramus and body implants Implant designs and concepts are developed from the work of Terino, 6,7 Whitaker, 8 Aiche, 9 Taylor and Teenier, 10 and Ramirez, 11 as well as the work of the senior author 12. Ramus and body implants are designed to change the shape of the mandible in three dimensions (bigonial width, ramus height, and body length), as well as inclination of the mandibular border (Figure 1). Increase in bigonial distance (or posterior width) is determined by the thickness of the implant (dimension A ). Increases in ramus height and body length result from flanges designed at the inferior (dimension B ) and posterior (dimension C ) borders of the implant, respectively. The implant length (dimension D ) will determine how much the anterior mandibular body will be impacted by the implant. Its tapering projection beyond the inferior edge of the mandible ( B ) allows it to change the inclination plane of the mandibular border. Because it also projects beyond the posterior border, in addition to extending beyond the inferior ramus edge, it can lessen the obliquity of the mandibular angle. The implant is used with a chin implant for deficient mandibles. 540 Aesthetic Surgery Journal ~ September/October 2007 Volume 27, Number 5

3 Chin implants We use an extended chin implant design with an external shape resembling the natural mandible. 11 It resembles the popular extended silicone chin implant design but differs in two important aspects. The chin implant comes in two pieces, a right and left half; the segmentation facilitates placement of the relatively long and stiff porous implant. The two-piece design also provides flexibility in positioning the lateral implant extensions, ensuring that it mimics the inclination of the patient s mandibular border (Figure 2). The manufacturer provides a tab insert designed to lock the right and left halves, effectively making it a onepiece implant. We rarely use this connecting tab because it dictates the position of the lateral implant limbs, as well as its width at the central portion. Operative Technique Anesthesia Illustrations by William M. Winn, Atlanta, GA Figure 1. Generic mandibular ramus and body implant used to augment the deficient mandible. The increase in bigonial distance (posterior width of the lower jaw) is determined by the thickness of the implant (dimension A ). Increase in ramus height and body length result from flanges designed at the inferior (dimension B ) and posterior borders (dimension C ) of the implant, respectively. The implant length (dimension D ) will determine how much of the anterior mandibular body will be impacted by the implant. Its tapering projection beyond the inferior edge of the mandible ( B ) allows it to change the inclination plane of the mandibular border. Because it also projects beyond the posterior border, in addition to extending beyond its inferior edge of the ramus, it can lessen the obliquity of the mandibular angle. The senior author prefers to perform mandible augmentation with the patient under general nasotracheal anesthesia, which provides a panoramic view of the operative field. The airway is protected while the face and oral cavity can be optimally prepared with an iodine solution after placement of a throat pack. The operative site is infiltrated with 1/200,000 epinephrine solution to aid in hemostasis. Incisions and exposure A generous intraoral mucosal incision is made at least 1 cm above the sulcus on its labial side to expose the ramus and body of the mandible (Figure 3). Unlike an Enlarging the Deficient Mandible Aesthetic Surgery Journal ~ September/October

4 Figure 2. This porous polyethylene chin implant has a two-piece design, which allows the lateral implant extension to follow the inclination of the mandibular border. A Masseter m. (reflected) Mandibular angle Subperiosteal dissection B Figure 3. A, A submental cutaneous incision is used to expose the chin. B, An intraoral mucosal incision, approximately 1 cm above the sulcus on its labial side, exposes the body and ramus. The entire anterior surface of the mandible is exposed in a subperiosteal plane. The mental nerve is identified and preserved. 542 Aesthetic Surgery Journal ~ September/October 2007 Volume 27, Number 5

5 incision made directly in the sulcus, this incision provides ample tissue on both its lingual and labial margins for suture closure. Furthermore, unlike the sulcus incision, there is no tendency for saliva to pool over the suture line with the potential to percolate through the incision and contaminate the implant. A submental incision is made for access and exposure of the anterior mandible and chin. We avoid an intraoral approach to the chin area because this has frequently damaged the mentalis muscle enough to result in chin ptosis and lip incompetence. The entire anterior surface of the mandible is exposed in a subperiosteal plane. It is important to free both the inferior and posterior mandible borders of soft tissue attachments to allow implant placement. The mental nerve is always visualized as it exits its foramen. A B 1/3 2/3 Adjusting the vertical chin height Patients with a deficient mandible frequently need vertical chin height adjustment before undergoing jaw augmentation. Vertical chin lengthening is achieved in those with inadequate vertical height via a horizontal chin osteotomy through the submental incision. The amount of chin lengthening is predetermined so that the distance from the base of the nose to the mouth opening will be half the distance from base of the nose to the end of the chin. (This is the average nose-to-mouth relationship in young North American Caucasians). 4 The position of the lowered (but not advanced) segment is fixed with titanium plates and screws. The space created by the bone movement is filled with a block of porous polyethylene, which adds stability to the construct and fills dead space (Figure 4, A). 14 Patients with mandibular deficiency and a long face frequently have increased vertical chin height, in part, because of the derotation of the mandible caused by the long midface. In these patients, the chin is shortened at its inferior border up to 5 mm. Later augmentation of the new chin point will support the relative excess of soft tissue created by the vertical reduction (Figure 4, B). 1/3 2/3 Figure 4. A, The vertical chin height is altered, if necessary, to normalize its dimensions so that the distance from the base of the nose to the mouth opening is about half the distance from the base of the nose to the end of the chin. Those with inadequate vertical height undergo vertical lengthening via a horizontal chin osteotomy through the submental incision. The position of the lowered (but not advanced) segment is fixed with titanium plates and screws. The space created by the bone movement is filled with a block of porous polyethylene, adding stability to the construct and filling dead space. B, Patients with mandibular deficiency and a long face frequently demonstrate an increase in vertical chin height caused partially by the derotation of the mandible, which in turn is caused by the long midface. The chin is shortened at its inferior border with a power saw or burr. When more than 5 to 7 mm are removed, the point of origin of the anterior belly of the digastric muscle is lost, resulting in retraction of this muscle and submental fullness. To avoid this problem, chin shortening that is greater than 7 mm requires a horizontal osteotomy with segment excision. Enlarging the Deficient Mandible Aesthetic Surgery Journal ~ September/October

6 Implant Positioning, Fixation, and Final Contouring To achieve desired implant placement and secure application, the implants are fixed to the mandible surface with titanium screws. Ramus and body Because the intraoral incision is remote from the posterior two thirds of this large implant, positioning and screw fixation of the ramus and body implants require vigorous retraction of the soft tissues. The implant is positioned so that the flange at its inferior border (dimension B, Figure 1), which will alter ramus height and border inclination, abuts on the inferior edge of the mandible border. For patients in whom the chin has been lengthened by horizontal osteotomy, the most anterior aspect of the mandible implant (dimension D ) will extend to the lateral edge of the lowered chin segment. This implant positioning camouflages the inevitable step off that occurs after horizontal osteotomy and movement of the chin. Because of limited surgical exposure, the drill holes for screw fixation are made obliquely through the implant and the skeleton, necessitating use of a long, guarded drill bit (Figures 5 and 6). Screws must be 10 to 12 mm in length to obliquely traverse the implant and Figure 5. Fixation of the mandible and chin implants. Screw fixation of the implant to the posterior mandible is performed through an intraoral approach. Because the intraoral incision is remote from the posterior two-thirds of this large implant, positioning and screw fixation of the ramus and body implants requires vigorous retraction of the soft tissues. A long, guarded drill bit is necessary to make drill holes for screw fixation because limited surgical exposure requires that the drill holes are made obliquely through the implant and then the skeleton. The implant is positioned so that the flange at its inferior border (dimension B, Figure 1), which will alter ramus height and border inclination, abuts on the inferior edge of the mandible border. In this case the chin has been lengthened after horizontal osteotomy and the most anterior aspect of the mandible implant (dimension D ) extends to the lateral edge of the lowered chin segment. This implant positioning camouflages the inevitable step-off that occurs after horizontal osteotomy and chin repositioning. The ghosted area demonstrates the area in which the implant will be placed to increase the vertical projection of the chin. Inset, The porous polyethylene chin implant is placed in a subperiosteal pocket. The two-piece design allows the lateral extension of the implant to follow the inclination of the mandibular border. The lateral aspect of the chin implant will extend to the anteriormost portion of the ramus and body implant. The chin implant is immobilized with screws, using the submental incision access. Note that because the contour of the posterior implant surface does not mimic the contour of the anterior mandible surface, there is a gap (green arrow on right) between the mandible and the implant. Screw fixation of the implant (shown on the left) will compress the implant to the skeleton and obliterate this gap. 544 Aesthetic Surgery Journal ~ September/October 2007 Volume 27, Number 5

7 Figure 6. Intraoperative photograph demonstrates mandible augmentation. The lower lip is retracted. The implant portion augmenting the mandibular body is exposed. Note the screw fixation. Figure 7. Intraoperative example of a screw-fixed two-piece porous polyethylene chin implant exposed through a submental incision. Screw fixation of the implant to the mandible prevents implant movement and obliterates gaps between the implant and anterior mandible surface. Figure 8. Intraoperative example of screw immobilized chin implant contoured with high speed burr. The inferior border is reduced to assure proper vertical chin height. Enlarging the Deficient Mandible Aesthetic Surgery Journal ~ September/October

8 A C E B D F G H Figure 9. A, C, E, Preoperative views of a woman with microgenia who had undergone bilateral upper and lower lid blepharoplasty, brow lift, and rhytidectomy 5 years ago. B, D, F, Postoperative views 6 months after 8-mm chin lengthening after horizontal osteotomy, sagittal augmentation with a 3-mm implant, and posterior mandible widening by 5 mm (each). The patient also underwent infraorbital rim and malar augmentation, midface elevation, lateral canthopexy, and lowering of the hair line and brows. (A secondary rhinoplasty was performed by another surgeon.) In this patient the chin has been lengthened after horizontal osteotomy; the anteriormost aspect of the mandible implant (dimension D ) extends to the lateral edge of the lowered chin segment. This implant positioning camouflages the inevitable step-off that occurs after horizontal osteotomy and chin repositioning. G, H, Pre- and postoperative diagrammatic representations. 546 Aesthetic Surgery Journal ~ September/October 2007 Volume 27, Number 5

9 A C E B D F G H Figure 10. A, C, E, Preoperative views of a 32-year-old woman with a long face and mandibular deficiency who had her class II occlusion normalized with orthodontic treatment in her youth. B, D, F, Postoperative views after 4-mm vertical shortening of the chin, 5-mm widening of the posterior mandible (on each side) and 5-mm lengthening, 9-mm sagittal chin augmentation, and submental lipectomy. G, H, Preoperative and postoperative diagrammatic representations. Enlarging the Deficient Mandible Aesthetic Surgery Journal ~ September/October

10 A C E B D F G H Figure 11. A, C, E, Preoperative views of a 48-year-old woman with normal skeletal dimensions who desired to increase definition and angularity of her lower jaw and undergo rhytidectomy. B, D, F, Postoperative views after rhytidectomy and sagittal chin augmentation with a 3-mm implant. The posterior mandible width was augmented 5 mm and vertically lengthened 3 mm. G, H, Preoperative and postoperative diagrammatic representations. 548 Aesthetic Surgery Journal ~ September/October 2007 Volume 27, Number 5

11 the mandible. In applying the implant to the skeleton, screw fixation eliminates any gaps between the implant and recipient bed. Gaps are potential sites for hematoma or seroma accumulation. More important, gaps may effectively result in increased augmentation. For example, a 2-mm gap between the posterior surface of a 5-mm implant would produce an augmentation equivalent to a 7-mm implant whose posterior surface was applied directly to the anterior surface of the skeleton. Usually, the senior author uses two screws to obliterate any gaps between the mandible and the implant, placing them to avoid the anticipated path of the inferior alveolar nerve before its exit from the mental foramen. It is crucial to soften any transitions between the implant and the mandible, particularly where the implant extends beyond the border of the anterior mandibular inferior edge. Any step-offs between the implant and mandible in this area may be visible in thin patients. Implant screw fixation allows for final contouring with scalpel or mechanical burr with the implants in place (Figures 7 and 8). Chin The chin and lower anterior mandible are accessed through the submental incision (Figure 5, Inset). The midline of the chin is scored with the drill on the pogonion as a reference point. Each half of the two-piece chin implant is positioned so that it extends from the midline, up to or before, but rarely overlapping, the anteriormost aspect of the ramus and body implant (which has already been positioned). The inferior border of the chin implant parallels and augments the inferior border of the native mandible while creating a smooth transition with the inferior border of the ramus and body implant. Wound Closure, Dressings, and Postoperative Care The intraoral incisions are closed in 2 layers with absorbable sutures, taking care to evert the mucosal edges. A small suction drain is left in until the next morning. The senior author prefers a drain with a trocar, which allows the skin exit site to be located behind the ear lobule. An elastic tape external dressing is used to help apply the soft tissues to the implant and avoid hematoma formation. Immediately before the procedure, broad-spectrum antibiotics (cephalosporins) are intravenously administered. Oral antibiotics are also administered for 5 days after surgery. The operative field and implants are not treated with antibiotic solutions. A liquid diet is prescribed for the first 3 days after surgery and a soft diet for the next 5 days. Frequent mouth washes are advised, as well as careful tooth brushing. Clinical Experience Using the techniques described, the senior author has enlarged 45 deficient mandibles during the last 3 years. The early appearance of these patients is not unlike those who have undergone wisdom tooth surgery. Most resume their usual activities between 1 and 2 weeks after surgery. There are no restrictions on activities at 3 weeks. Untoward sequelae have been uncommon. One patient (2%) presented infection at 2 weeks. Her implants were removed and then replaced 6 months later. Three patients (7%) had revisional surgery to correct malpositioned implants. There have been no materialsrelated problems. Various configurations of implants and manipulations of chin height are depicted in the clinical examples (Figures 9 to 11). Conclusion Patients with deficient mandibles and normal occlusion can normalize the dimensions of the lower face by undergoing alloplastic implant augmentation. Successful outcomes depend on knowledge of normal facial skeletal relationships, appropriately designed, biocompatible implants, and facility with craniofacial techniques. Dr. Yaremchuk became a consultant for Porex Surgical in June References 1. Yaremchuk, MJ. Atlas of facial implants. Philadelphia: Saunders- Elsevier, Farkas L, Hreczko TA, Kolar JC, Munro IR. Vertical and horizontal proportions of the face in young adult North American Caucasians: revision of neoclassical canons. Plast Reconstr Surg 1985;75: Farkas LG, Kolar JC. Anthropometrics and art in the aesthetics of women s faces. Clin Plast Surg 1987;14: Farkas LG, Hreczko TA, Katic MJ. Appendix A: Craniofacial norms in North American Caucasians from birth (one year) to young adulthood. In: Farkas LG, editor. Anthropometry of the head and face. 2nd ed. New York: Raven Press, Maas CS, Merwin GE, Wilson J, Frey MD, Maves MD. Comparison of biomaterials for facial bone augmentation. Arch Otolaryngol Head Neck Surg 1990;116: Terino EO. Alloplastic facial contouring: surgery of the fourth plane. Aesthetic Plast Surg 1992;16: Terino EO. Unique mandibular implants, including lateral and posterior angle implants. Facial Plast Surg Clin North Am 1994;2: Whitaker LA. Aesthetic augmentation of the posterior mandible. Plast Reconstr Surg 1991;87: Aiche AE. Mandibular angle implants. Aesthetic Plast Surg 1992;16: Enlarging the Deficient Mandible Aesthetic Surgery Journal ~ September/October

12 10. Taylor CO, Teenier TJ. Evaluation and augmentation of the mandibular angle region. Facial Plast Surg Clin North Am 1994;3: Ramirez OM. Mandibular matrix implant system: a method to restore skeletal support to the lower face. Plast Reconstr Surg 2000;106: Yaremchuk MJ. Mandibular augmentation. Plast Reconstr Surg 2000;106: Zide BM. The mentalis muscle: An essential component of chin and lower lip position. Plast Reconst Surg 1989;83: Wolfe SA, Posnick JC, Yaremchuk MJ, Zide BM. Chin augmentation. Aesthetic Surg J 2004;24: Reprint requests: Michael J. Yaremchuk, MD, Massachusetts General Hospital, Fruit Street, Boston, MA Dr.y@dryaremchuk.com. Copyright 2007 by The American Society for Aesthetic Plastic Surgery, Inc X/$32.00 doi: j.asj Aesthetic Surgery Journal ~ September/October 2007 Volume 27, Number 5