Mandibular Implants

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.

Biomaterials