Facts on Facial Implants

Virtually all aesthetic facial skeletal augmentation is done with alloplastic materials. The use of synthetic material avoids donor area morbidity while vastly simplifying the procedure in terms of time and complexity.  Implant materials used for facial skeletal augmentation are biocompatible – that is, they have 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 minimal and predictable effect on the host tissue which surrounds it. This type of relationship is an advantage over the use of autogenous bone or cartilage which, when revascularized by surrounding tissues allows it to be remodeled to varying degrees, thereby changing volume and shape.

The currently used alloplastic implants used for facial reconstruction have not shown to have any toxic effects on the patient.  The body 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 which 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 which results in a less dense capsule .

^{                      Â}  The two most commonly used materials for facial skeletal augmentation are silicone and porous polyethylene (Omnipore, Medpor). Each has its advantages and disadvantages. Therefore, each has its surgical proponents and detractors.

Polysiloxane is a polymer created from interlinking silicone and oxygen (S₁O(CH₃)₂] with methyl side groups and, as such, is the only non-carbon chain polymer used in medical implantation. Solid silicone or the silicone rubber used for facial implants is a vulcanized form of polysiloxane.

CH₃

_↓

S_1→O

_↓

CH₃

            Solid silicone has the following advantages:  it can be sterilized by steam or irradiation, it can be carved with either a scissors or scalpel, and it can be stabilized with a screw or a suture.  Because it is smooth, it can be removed quite easily.  Disadvantages include the tendency to cause resorption of bone underlying it, particularly when used to augment the chin, the potential to migrate if not fixed, and the potential for its fibrous capsule to be visible when placed under a thin soft tissue cover.

Polyethylene

Polyethylene is a simple carbon chain of ethylene monomer.  The high density, porous variety – Medpor, Omnipore – is used for facial implants because of its higher tensile strength.

H     H

_{↓      ↓}

_→C_→C_→

_{                                                                                                    ↓↓}

H    H

Polyethylene has a firm consistency resisting material compression while still permitting some flexibility.  The porosity of porous polyethylene has both advantages and disadvantages. The advantages of porous polyethylene include its tendency to allow extensive soft tissue ingrowth, thereby lessening its tendency to migrate and to erode underlying bone. Its firm consistency allows it to be easily fixed with screws and contoured with a scalpel or power equipment without fragmenting.  However, its porosity causes soft tissue to adhere to it, making placement more difficult and requiring a larger pockets to be made than with smoother implants. The soft tissue ingrowth also makes implant removal more difficult than with smooth surface implants.

In most applications porous polyethylene is preferred by this surgeon. Because of its firmer consistency and materials properties, it more resembles bone – the tissue that it is imitating.  It also allows easy adjustment to its shape and profile with scalpel or mechanical bur thereby making the procedure for custom or “bespoke’ for each patient.  It is true that implant removal is more difficult when the material has been in place for prolonged periods. However this surgeon undertakes a procedure with the idea of providing an optimal initial result – one unlikely to be discarded later. In the rare occasion when infection occurs, it always occurs soon after surgery – before any ingrowth occurs, making removal straightforward.