Introduction

Augmentation is the predominant means of aesthetic contouring of the facial skeleton in non-Asian populations. Conceptually, autogenous bone would be the best material for augmentation, because it has the potential to be revascularized and, then, incorporated into the facial skeleton. In time, it could be biologically indistinguishable from the adjacent native skeleton. Practically, the use of autogenous bone is limited. The morbidity, time and hospital costs associated with autogenous bone graft harvest can be significant. Furthermore, the inevitable resorption and the poor handling characteristics of autogenous bone grafts also limit the quality and predictability of the aesthetic result. For these reasons, almost all facial skeletal augmentation is done with alloplastic implants. A diagrammatic survey of the facial skeletal areas amenable to augmentation with alloplastic implants is presented in Fig. 14.1.

Fig. 14.1 A diagrammatic survey of the alloplastic implants used for facial skeletal enhancement. Anatomic areas include the infraorbital rim, malar, pyriform aperture, chin as well as the mandibular body and ramus.

Indications

• Facial skeletal augmentation is most often done to enhance facial appearance in patients whose skeletal relationships are ostensibly within the normal range. These patients want more definition and angularity to their appearance. Other patients desire to “balance” their facial dimensions.

• Craniofacial deformities which are disfiguring and are of functional consequence to vision, breathing, and mastication, usually require skeletal osteotomies and rearrangement as treatment. In patients with less severe midface or mandibular hypoplasia, occlusion is normal or has been compensated by orthodontics. These patients have neither respiratory nor ocular compromise. In these patients, the appearance of skeletal osteotomies and rearrangements can be simulated through the use of facial implants. Diagrammatic representations of how implant surgery can mimic the appearance of skeletal osteotomies are shown in Figs 14.2 and 14.3.

Fig. 14.2 Diagrams show how multiple implant augmentation of the midface skeleton can simulate the visual appearance of LeFort III osteotomy and advancement without altering dental occlusion. A, Illustration of midface concavity and Class III malocclusion. B, Osteotomy and advancement at the LeFort III level provides midface projection and Class I occlusion. C, Illustration of midface concavity and Class I occlusion. D, Multiple midface implants provide visual effect of LeFort III osteotomy and advancement but does not alter occlusion.

Fig. 14.3 Diagrams show how multiple implant augmentation of the mandible can simulate the visual appearance of of sagittal split osteotomy and horizontal osteotomy of the chin without altering dental occlusion. A, Mandibular deficiency with Class II occlusion. B, After sagittal split osteotomy with horizontal osteotomy and advancement of the chin to increase chin projection. Note that the occlusion has been corrected from Class II to Class I. C, Mandibular deficiency with Class I occlusion. D, The visual effect of sagittal split osteotomy and horizontal osteotomy of the chin with advancement has been simulated with mandible and chin implants. Note that the Class I occlusion is unchanged. Notice also that the border regularities inherent with skeletal osteotomies are avoided when implants are used.

Preoperative Evaluation

Surgical Planning

For most reconstructive problems, surgery is performed to return the involved area to its original appearance, or, if that is not possible, to one that is symmetric and accepted as normal. When alloplastic implants are used to make the face more attractive, the aesthetic goal is more arbitrary. Because implant augmentation of the facial skeleton results in measurable changes in facial dimensions and proportions, it is intuitively advisable and appropriate to use facial measurements to evaluate the face and to guide surgery.

Facial anthropometries and neoclassical canons

For purposes of painting and sculpture, Renaissance scholars and artists formulated ideal proportions and relations of the head and face. These were largely based on classical Greek canons. Although usually referenced in texts discussing facial skeletal augmentation, neoclassical canons have a limited role in surgical evaluation and planning, because they are based on idealizations. When the dimensions of normal males and females were evaluated and compared to these artistic ideals, it was found that some theoretic proportions are never found, and others are one of many variations found in healthy normals, or those determined more attractive than normals.^1,2 The neoclassical canons do not allow for the facial dimensions that are known to differ with sex and age. Most of these canons of proportion (e.g. the width of the upper face is equal to five eye widths), are interesting but hold for few individuals and cannot be obtained surgically or, if obtainable, only with extremely sophisticated craniofacial procedures. For these reasons, we have found it more useful to use the anthropometric measurements of normal individuals to guide our Gestalt in the selection of implants for facial skeletal augmentation (Fig. 14.4).³ Normal dimensioned faces are intrinsically balanced. That is, the relations between the various areas of the face relate to one another in a way that is not distracting to the observer. By comparing a patient’s dimensions to the average, the surgeon has some objective basis as to what anatomic area may be amenable to augmentation, and by how much.

Fig. 14.4 Frontal and lateral views of female and male faces drawn from average anthropometric measurements for 21 year old North American Caucasians. Measurements are in millimeters. A, Frontal view female. B, Frontal view male. C, Lateral view female. D, Lateral view male.

Alloplastic Materials

Implant materials used for facial skeletal augmentation are biocompatible – that is, there is an acceptable reaction between the material and the host. In general, the host has little or no enzymatic ability to degrade the implant with the result that the implant tends to maintain its volume and shape. Likewise, the implant has a small and predictable effect on the host tissues that surround it. This type of relationship is an advantage over the use of autogenous bone or cartilage which, when revascularized, will be remodeled to varying degrees, thereby changing volume and shape.

The presently used alloplastic implants used for facial reconstruction have not been shown to have any toxic effects on the host.⁴ The host responds to these materials by forming a fibrous capsule around the implant, which is the body’s way of isolating the implant from the host. The most important implant characteristic that determines the nature of the encapsulation is the implant’s surface characteristics. Smooth implants result in the formation of smooth-walled capsules. Porous implants allow varying degrees of soft tissue ingrowth that results in a less dense and defined capsule. It is a clinical impression that porous implants, as a result of fibrous incorporation rather than encapsulation, have a lower tendency to erode underlying bone or migrate due to soft tissue mechanical forces and, perhaps, are less susceptible to infection when challenged with an inoculum of bacteria. The most commonly used, commercially available materials today for facial skeletal augmentation are solid silicone, and porous polyethylene -Medpor (Porex, Fairborn, GA). Eppley⁵ has summarized the attributes of these materials.