Breast Implant Generations

Second-generation devices were modified in an attempt to improve the rate of capsular contracture. These devices were designed with a much thinner shell (0.13 mm versus 0.25 mm average thickness) and a less viscous gel, and the Dacron patches were removed (5). The first second-generation device was Dow Corning's Silastic I. It was introduced in 1972, and manufacturing of the Silastic I overlapped with the production Silastic 0 and was produced until 1986. It did not provide any appreciable reduction in the incidence of capsular contracture and reportedly had a higher incidence of rupture that was attributed to the strength of its shell (5).

The phenomenon of gel bleed was realized in the 1970s (5,12-14). Gel bleed is the diffusion of non-cross-linked silicone oil from the gel across the elastomer shell into the surrounding environment. Although the significance of this phenomenon remains unclear today, it stimulated manufacturing changes that are characteristic of third generation devices. Thicker, reinforced barrier shells characterize third-generation devices. The thickness and strength improvements were developed out of concern for shell failure with second-generation devices. Shell strength was improved by reinforcing the elastomer composition with silica (1). Creating a barrier to gel diffusion with phenyl or triflouropropyl groups bonded to the shell surface reduced diffusion of non-cross-linked silicone (2,3). These properties are retained in current manufacturing processes. It is important to keep in mind that gel bleed is a function of diffusion of silicone oil across the elastomer. The gel bleed does not change based on the viscosity (degree of cohesion of the gel filler).

Saline-filled breast implants were first manufactured in France in 1964, introduced by Arian with the goal of being surgically placed via smaller incisions. These devices had a high failure rate and were discontinued in the early 1970s (5). Heyer-Schulte was the first U.S. manufacturer of saline-filled devices. The original devices consisted of thin shells created through a high temperature vulcanization (HTV). These devices were prone to spontaneous deflation (5). Modifications in the shell manufacturing have allowed the high success rates that characterize modern saline-filled devices. The current devices are manufactured with thicker, room temperature vulcanized (RTV) shells.

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