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Silicone

Silicone Gel Implants

As a medical device technology, there are five generations of silicone breast implant, each defined by common model-manufacturing techniques.

First Generation Silicone Implants

1963 saw the introduction of the Cronin–Gerow Implant. It was a tear-drop-shaped sac (silicone rubber envelope) filled with viscous silicone-gel. To reduce the rotation of the emplaced breast-implant upon the chest wall, it was affixed to the implant pocket with a fastener-patch of Dacron material (Polyethylene terephthalate) attached to the rear of the breast implant shell.

Second Generation Silicone Implants

In the 1970s, the first technological development came along. A thinner device-shell and a thinner, low-cohesion silicone-gel filler improved the functionality and verisimilitude (size, look, and feel) of the silicone breast implant. Yet, in clinical practice, the second-generation proved fragile, and suffered greater incidences of shell rupture, and of “silicone gel bleed” (filler leakage through an intact shell).

The increased incidence-rates of medical complications (e.g. capsular contracture) precipitated U.S. government faulty-product class-action lawsuits against the Dow Corning Corporation, and other manufacturers of breast prostheses.

The second technological development was a polyurethane foam coating for the implant shell; it reduced the incidence of capsular contracture by causing an inflammatory reaction that impeded the formation of a capsule of fibrous collagen tissue around the breast implant.

Nevertheless, the medical use of polyurethane-coated breast implants was briefly discontinued because of the potential health risk posed by 2,4-toluenediamine (TDA), a carcinogenic by-product of the chemical breakdown of the implant’s polyurethane foam coating.

After reviewing the medical data, the U.S. Food and Drug Administration concluded that TDA-induced breast cancer was an infinitesimal health-risk to women with breast implants, and did not justify legally requiring physicians to explain the matter to their patients. In the event, polyurethane-coated breast implants remain in plastic surgical practice in Europe and in South America; in the U.S., no breast implant manufacturer has sought the FDA’s approval for American medical sale.

Third Generation Silicone Implants

The third technological development was the double lumen breast-implant, a double-cavity device composed of a silicone-implant within a saline-implant.

The two-fold technical goal was to provide:

(i) the cosmetic benefits of silicone-gel (the inner lumen) enclosed in saline solution (the outer lumen);

(ii) a breast-implant device the volume of which is post-operatively adjustable.

However, the more complex design of the double-lumen breast-implant suffered a device failure rate greater than that of single-lumen breast implants. The contemporary versions of second generation devices, presented in 1984, are the “Becker Expandable” models of breast implant devices, used primarily for breast reconstruction.

Third And Fourth Generation Silicone Implants

In the 1980s, the models of the third and of the fourth generations of breast-implant devices were sequential advances in manufacturing technology, e.g. elastomer-coated shells that decreased gel-bleed (filler leakage), and a thicker filler (increased-cohesion) gel.

Sociologically, the manufacturers then designed and fabricated varieties of anatomic models (closer to the shape of a natural breast) and shaped models (round, tapered) that corresponded with the breast and body types presented and required by women patients.

The tapered models of breast implant have a uniformly textured surface to reduce rotation; the round models of breast implant are available in smooth-surface and textured-surface types.

Fifth Generation Silicone Implants

Since the mid-1990s, the fifth generation of silicone breast implant is made of a semi-solid gel that mostly eliminates filler leakage (silicone gel bleed) and silicone migration from the breast to elsewhere in the body. The studies Experience with Anatomical Soft Cohesive Silicone Gel Prosthesis in Cosmetic and Reconstructive Breast Implant Surgery (2004) and Cohesive Silicone gel Breast Implants in Aesthetic and Reconstructive Breast Surgery (2005) reported low incidence rates of capsular contracture and of device-shell rupture, improved medical safety and technical efficacy greater than earlier generations of breast implant device.