Answer:
The advantages of alloplastic techniques versus bone grafting techniques include their ready exchangeability and reversibility.
An ideal implant should be (1) easy to place, (2) nonpalpable, (3) readily exchangeable, (4) malleable and conformable, (5) biocompatible, and (6) modifiable by the surgeon. Smooth silicone implants become fixed rapidly and securely by circumferential fibrosis (capsule formation). They can be exchanged or removed easily when necessary. On the other hand, porous implants permit ingrowth. Examples are Proplast, Porex, and Hydroxyapatite, as well as fenestrated implants or implants with Dacron backing. Tissue ingrowth makes implants more difficult to exchange.
Ideal facial implants should be malleable and compressible enough to allow insertion through small incisions. Limited incisions minimize extrusion. Silicone rubber implants fabricated with a medium-grade consistency make it possible to perform the above procedures with ease and with minimal morbidity.
The entire mandibular contour can also be altered. Lateral extensions on a conventional chin implant create a lateral widening to the lower third of the face. Traditional chin implants have lacked the ability to extend the chin in a vertical direction. However, a new implant design is now available which wraps around the inferior bony margin of the chin. It increases the vertical height of the face from the lower lip to the inferior border of the bony chin. The ideal procedure in these patients is always osseous genioplasty, but some camouflage can be achieved with the aforementioned implant. In the central premandible region, 5 to 7 mm of projection are most suitable for the majority of patients. For severe microgenia, 8 to 10 mm are necessary. It should be noted that once the intended augmentation approaches 10 mm, the patient may be better served by an osteotomy.
Basic principles:
1. Stay on bone. When implants are placed directly on bone, the capsule that forms is less apparent since the full thickness of the soft tissue is available to disguise it.
2. Avoid trauma to the soft tissue, which could produce mental nerve injury.
3. Expand the pocket adequately to accommodate the chosen prosthesis, but do not make the pocket any larger than absolutely necessary.
4. Minimize bleeding by keeping the dissection immediately on the bone and by using an injection of an epinephrine-containing solution.
The premandible space can be accessed by either the standard intraoral route or the submental route. In our experience, for a procedure that requires a submental approach, such as submental liposuction or platysma plication, the submental approach is used.
In either case, the incision is 2 cm long and transverse. The intraoral incision is through mucosa only. The mentalis muscles are then divided vertically through their midline raphe to avoid unnecessary injury or disinsertion of this muscle.
The incidence of complications:
1. Patient and/or doctor dissatisfaction: 10–20%.
2. Asymmetry: 10–15%.
3. Malposition: 10%.
4. Hematoma, seroma, and infection requiring removal: 1.5%.
5. Mental nerve temporary dysfunction (intraoral route): 1–2%.
6. Lip temporary dysfunction (intraoral route): 1%.