Materials

A polymer consists of long chains of repeating subunits. Carbon, hydrogen, and oxygen are the typical constituents, but exceptions are noted in the following discussion. Stability of the material is related to the length of the chains and to the number of cross-bridges between chains. The more stable the material, the less likely it is that the body will break it down.30 The most common polymers used for nasal implantation include silicone, polytetrafluoroethylene (PTFE), and polyethylenes.

SILICONE

Silicone refers to a group of polymers. Silicon is the fundamental element of this group. Silica, SiO2, is polymerized with methyl groups to form silicone. Extending the length and cross-linking of the polymer affects the form the material takes. Progressive formation of silicone gel and silicone rubber is the result. The material's form has a significant influence on acceptance by host tissue. Silicone rubber is nonporous and does not form particles. Silicone gel has been used primarily for breast augmentation, but it has also been used in a cured form to improve nasal contour.31 The risk of migration and significant inflammatory reaction has been documented in the literature and should therefore preclude its use in this form. Because it lacks pores and is relatively stable, silicone rubber or Silastic is less likely to initiate an inflammatory response by the recipient. This material has been used extensively for dorsal, tip, and premaxillary augmentation.21'32-35 The non-porous nature of silicone reduces the probability for bacterial colonization, but it also impedes tissue ingrowth. Lack of ingrowth may lead to movement of the implant and will induce capsule formation around the implant. The capsule can be a site of bacterial infiltration, acts as a barrier against penetration of antibiotics, and can lead to implant distortion. The risk of extrusion remains for the life of the patient and has been reported as long as 20 years after implantation.36-38

The most common use for silicone is for combined dorsum and tip augmentation, and it has been used extensively for Asian nose rhinoplasty.35 Silicone rubber possesses the advantage of being easily carvable and autoclavable. The method of placement depends on its use. Patients must be informed of the inherent risks of the use of these implants. However, solid silicone should not be lumped into the same category as the breast implant gel and is an excellent material for chin augmentation. Silicone has been used successfully in Asian patients undergoing augmentation rhinoplasty. These patients have thicker skin and are better able to support an alloplastic implant than are thin-skinned patients. However, we prefer to use autologous or homologous materials whenever possible.

POLYTETRAFLUORETHYLENE

Several implant materials fall into the category of PTFE. The most notable are Teflon, Proplast, and Gore-Tex, all of which consist of fluorine-carbon polymers. The bond between these two elements is very strong and therefore stable, despite the lack of fluorine or fluorinelike substances in the body. GoreTex is the most widely used PTFE implant material for the nose and, as such, is discussed in detail.

Proplast is a black-colored implant material, which is fairly rigid and easily visible through thin skin, making its use impractical in dorsal nasal augmentation.39,40 Proplast II was developed 10 years after Proplast. It is composed of PTFE linked to aluminum oxide fibers and hydroxyapatite, to give it a white color and to allow for bone compatibility, respectively.41 Proplast II is more rigid than Proplast and is more porous, allowing for increased tissue ingrowth. The increased porosity may also be the reason for its propensity for fragmentation and severe inflammatory reactions when subjected to shearing-type forces as demonstrated with replacement of the temporomandibular joint (TMJ).42-51 Because of the significant problems associated with TMJ reconstruction, Proplast is no longer available as an implant.

Gore-Tex has been the most promising implant in the PTFE group. It has been used extensively as a vascular graft since the early 1970s, and more recently as a facial implant. Subcutaneous augmentation material (SAM) was approved in 1993 for use in facial augmentation, including nasal augmenta-tion.52 Gore-Tex is a derivative of Teflon, made up of repeating units of carbon bound to fluorine. The material's interweaving fibrillar makeup along with relatively small pores (22 ^m) allows for stabilizing tissue ingrowth without significantly inhibiting removal if necessary.53 Gore-Tex is also hydrophobic, which inhibits bacterial adherence and reduces the severity of tissue ingrowth, again, facilitating its removal. In the rabbit model, Gore-Tex has been shown to elicit minimal inflammation when evaluated grossly and histologically.54,55 The stability of Gore-Tex is a result of polymerization of repeating units of carbon bound to fluorine. Although fluorine is not found normally within human tissue, the material remains relatively inert as a result of its extremely strong carbon-fluorine bonding.

Indications for the use of Gore-Tex have expanded. The evolution from abdominal wall patch to use in facial augmentation and reconstruction blossomed during the early to mid-1980s. SAM is identical to the soft tissue patch and is used specifically for facial plastic and reconstructive surgery. Gore-Tex implants have been used for a myriad of applications in facial plastic surgery but have found significant success when used to augment the nasal dorsum.14,56-61 Because of its natural appearance and ease of use as compared with rib cartilage or other autolo-gous implants, Gore-Tex has become popular as a nasal implant.

SAM can be easily carved and shaped to camouflage defects in the nasal dorsum. The material is manufactured in 1-, 2-, and 4-mm thickness, which can be beveled at its periphery to blend with surrounding tissue.55 Because of its ease of use and natural appearance, it has quickly become the alloplastic implant of choice for many facial plastic and reconstructive surgeons. However, we prefer to use autologous materials whenever possible.

POLYETHYLENES

Polyethylene implants are composed of a group of polymers with different characteristics based on their length, density, and cross-linkages. Three different densities have been described: low-, medium-, and high-density polymers.62 The high-density polymers are the most often used for reconstructive craniofa-cial surgery. Medpor (Porex, Fairburn, GA) and Plastipore (Richards Manufacturing Company, Memphis, TN) are examples of high-density polyethylene implant materials. Medpor and Plastipore are flexible but maintain their shape when manipulated.63 They have pores ranging in size from 100 to 250 ^m, which allows for significant soft tissue and bone ingrowth.64-67 Because of its stiffness, the implant appears unnatural over the nasal dorsum.21

POLYESTERS AND POLYAMIDES

Polyethylene terephthalate can be woven into a nonresorbable mesh referred to as Mersilene (Ethicon, Somerville, NJ) for dorsal nasal and subnasal region implantation.68,69 The implant material allows for significant tissue ingrowth, maintaining implant position, but also making its removal difficult when necessary.70 The mesh permits bacteria to grow within its network of fibers, leading to significant problems with bacterial colonization, infection, and graft failure.71 Because of these factors, placement over the nasal dorsum is not recommended. Polyamides include a sim ilar substance to Mersilene mesh with the trade name Supramid (Ethicon) mesh. Both have similar qualities and appearance. Supramid, however will resorb leaving behind a fibrous shell to maintain some of the implant's original volume.21

this manner would most certainly be more expensive than other alternatives, but the future may also supply more efficient and cost effective methods for producing bioengineered implant materials.

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