Over the past two decades, great improvements have been made in the design of facial implants. Facial implants are able to enhance facial contour and provide permanent volumetric replacement. Facial implants can be used in many anatomic regions of the face, including the cheek, midface, nose, and mandible. Here we discuss the application of implants for the correction of profile imbalance as well as the rejuvenation of the lower third of the face. Mandibular augmentation is perhaps the simplest and most powerful aesthetic procedure available to the surgeon. Mentoplasty can create a stronger mandibular profile and improve the appearance of the nose by making it appear smaller and less imposing. In addition, augmentation of the prejowl sulcus and the mandibular angle can help enhance the effects of rhytidectomy by creating a sharper cervicofacial angle. Successful surgical results will be determined by the proper technique. The goals of mandibular augmentation are to reconstruct facial contour deformities or deficiencies with a high degree of predictability.
General Considerations
Indications for Mandibular Augmentation
The primary indications for mandibular augmentation include:
- 1
Stand-alone procedure for mandibular augmentation
- 2
Adjunctive procedure to rhinoplasty with an emphasis on profileplasty
- 3
Adjunctive procedure to rhytidectomy, which is often essential for patients with microgenia and/or prominent prejowl erosion
The key to mandibular augmentation lies in the restoration of anterior projection and/or expansion of lateral contour. In the aging process, the anterior mandible may develop flattening of the soft tissue button of the chin and form a deepening of the prejowl sulcus.
Augmentation of the bony mandible occurs over one of three zonal areas ( Figure 17-1 ). The first zone is the central chin area, which extends from the mentum to mental foramen (Zone 1). The midlateral zone is defined by a line extending from the mental formen posteriorly to the oblique line of the horizontal body of the mandible (Zone 2). The third and last zone of the premandibular space ecompasses the posterior half of the horizontal body, including the angle of the mandible and the first 2 to 4 cm of the ascending ramus (Zone 3).
Augmenting a recessed central chin area is a key componenet of profileoplasty which can additionally improve the aesthetic outcome of rhinoplasty. The projection of the chin directly affects the illusory projection of the nose in an inverse relationship. The traditional chin implants, placed only within the central area (Zone 1) without lateral extension into the midlateral zones (Zone 2) often created suboptimal results ( Figures 17-2 to 17-4 ). These early implants, unidimensionally designed and with a single vector, were often bulky and nonanatomic. This often resulted in a round chin protuberance, which can appear abnormal and unattractive. Similarly, a smaller implant, placed centrally had a greater tendency to shift or rotate than a larger more extended implant.
Most of these early problems were corrected with the design of the extended mandibular implants that occupied Zones 1 and 2. Placement of an implant that extends into at least two zones (central chin and midlateral) also results in a natural widening of the anterior jawline as well as an increased vertical dimension of the lower third of the face ( Figure 17-5 ).
Augmentation of the posterior-lateral zone widens the jaw to produce a stronger posterior jawline contour. This can be achieved using a mandibular angle implant to augment the posterior lateral zone of the mandible (the posterior half of the horizontal body including the angle of the mandible and the first 2 cm to 4 cm of the ascending ramus).
Mentoplasty can also have a powerful impact in facial rejuvenation in addressing the structural elements of the jaw and neck. The prejowl and prejowl–chin implants can be used as stand-alone procedure or serve a complementary role to liposuction and rhytidectomy ( Figures 17-6 to 17-8 ). Causative factors leading to the aging and ptotic face include loss of volume or atrophy of soft tissue and skin elasticity overlying Zones 1 and 2 of the mandible. Over the lower third of the face, this is seen as a loss of a straight jaw line and the development of jowling, prejowl sulcus, and/or marionette lines (skin crease that extends from the oral commissure to the mandible). The marionette lines emerge due to the attachment of the depressor labii inferiorus muscle and depressor angulii oris to the inferior mandible. These attachments create a point resistance by which drooping skin is caught producing a “hammock”-like bulge of skin. By removing these attachments, the skin is allowed to fall more naturally and the marionette lines are reduced or softened.
Careful evaluation leads to realization that an area of volume deficiency exists anterior to the jowl called the prejowl sulcus. The prejowl sulcus is a specific area anterior to the jowl exhibiting a marked dropoff in soft tissue volume and bony mandibular projection. The sulcus or depression can occur from several factors such as a deficiency of bone, congenitally narrow mandible, or aggregation of soft tissue around the mandibular ligament that contributes to the jowl. The skin overlying the prejowl sulcus is also significantly thinner than the skin lateral or medial to this location. As the aging process advances, the anterior mandibular groove deepens, which further accentuates the jowls.
Treatment of mandibular jowling and creation of a smooth mandibular line primarily require rhytidectomy, which repositions and tightens the soft tissue along the lower third of the face. Rhytidectomy alone, however, may not completely address the prejowl sulcus. Therefore, a secondary procedure that directly addresses this defect using a prejowl implant is required. A series of prejowl and chin implants have been designed for this use. The implants used in conjunction with facelift surgery increase its ability to create a smooth and straight jaw line.
Implant Characteristics
The ideal implant material for bony manidibular augmentation should be inert, easily shaped, conformable yet able to maintain its desired shape over the long term ( Figure 17-9 ). The implant should be easily customized and modified for the needs of the patient while not compromising the integrity of the implant. Implant immobilization is partly related to the degree of encapsulation. All implants have some level of encapsulation. Implants made from silicone elastomer have a high degree of encapsulation, while implants made from polytetrafluoroethylene (ePTFE; W.L. Gore & Asssociates, Inc., Flagstaff, AZ) encapsulate to a lesser degree yet provide some fixation with minimal tissue ingrowth. Each implant material causes unique tissue–implant interactions. Ideal tissue–implant interaction will not cause significant tissue ingrowth and permanent fixation of the implant. As with any implantable material, ease of removal and replacement is essential to the quality of any implant, whether it be a breast implant or cardiac pacemaker. In aesthetic surgery, it is particularly important if the patient desires further change.
The shape of the implant should also have tapered edges to ensure a smooth transition from implant to bony foundation. In newer generations of silicone implants, design efforts are focused on making the undersurface of the implant more malleable. Greater conformation to the irregular bony surfaces of the mandible prevents the formation of dead space and thereby reduces the movement and migration.
Implant Composition
Biomaterials
Polymetric Materials
In use since the 1950s, silicone has proved to be a safe and effective implant material. Silicone is polymerized dimethylsiloxane and can take the form of a gel, solid, or liquid depending on the degree cross-linking and polymerization. The gel form of silicone has the potential to leak, but the most recent studies finds no cause-and-effect relationship between silicone and the development of lupus, scleroderma, or other autoimmune diseases. Solid silicone has a higher degree of inertness than gel silicone with no evidence of toxicity or allergic reactions. Tissue reaction to solid silicone consists of the formation of a fibrous capsule around the implant but without tissue ingrowth. Capsular contraction and secondary implant deformity are rare and occur secondary to an implant that is placed improperly at a superficial plane. Seroma formation or inflammatory tissue reaction usually occurs as a result of implant mobility.
Polymethacrylate (Acrylic) Polymers
These can be supplied as a powdered material or preformed. The powder is mixed at the time of surgery to form a hard material. Due to its rigidity, placement of larger implants through relatively smaller openings can be difficult and even impossible. Preformed implants also lack the ability to conform to the vagaries of underlying bone.
Polyethylene
In the porous form, also known as MEDPOR (Porex Surgical, Inc., Newnan, GA), polyethylene can be developed to take on a variety of forms and consistencies. It elicits minimal amounts of inflammatory cell reaction. The material is rigid and thus difficult to mold to fit the underlying bony foundation. The porosity of the implant allows for significant tissue ingrowth and tissue stability, but as a drawback the biomaterial is therefore difficult to remove.
Polytetrafluoroethylene
Formerly marketed under the brand name of Proplast, this group of materials is no longer marketed in the United States secondary to its complications with temporomandibular joint use. Under high mechanical stress, this implant often broke down and elicited intense inflammatory reaction, thick capsule formation, and extrusion
Expanded Polytetrafluoroethylene (ePTFE)
Originally produced for cardiovascular applications, this material has the benefit of producing minimal tissue ingrowth, capsule formation and inflammatory reaction. Given its limited tissue ingrowth, ePTFE is ideally suited for subcutaneous tissue augmentation where ease in secondary modification or removal may be desired.
Mesh Polymers.
The mesh polymers include Marlex (Chevron Phillips Chemical Company, The Woodlands, TX), Dacron (Unify, Inc., Greensboro, NC), and Madrilène (Ethicon, Cincinnati, OH). They have similar advantages of being able to be folded, sutured, and shaped with ease. Unfavorable characteristics include ingrowth of fibrous tissue. Supramid (Resorba Wundversorgung, Nurnberg, Germany) is a polyamide mesh derivative of nylon that is unstable in vivo. It elicits a mild foreign body reaction and over time causes implant degradation and resorption.
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