The biology and evolution of cohesive gel and shaped implants.

The introduction of the silicone gel implant in 1962 began the modern era of breast augmentation, and over the past 50 years, breast implants have evolved to encompass a wide array of commercially available implants today. In April 1992, the moratorium on silicone gel breast implants began, and much of the experience and development of the cohesive shaped implants occurred outside the United States. During this time, saline implants were used almost exclusively in North America, whereas silicone implants continued to be used throughout the rest of the world. In 2001, cohesive gel implants became available in the United States under an Investigational Device Exemption Study. Three companies have US Food and Drug Administration approval of fifth-generation implants: Sientra, Allergan, and Mentor. These implants are unique due to the texture of the shell, implant dimensions, gel-shell interaction, gel fill ratio, degree of cross-linking, and form stability. Although form stability is a relative term, it may best be reserved to describe the increased ability of the implant to maintain its basic, intended shape. The cross-linking, form stability, and cohesiveness of these fifth-generation implants provide surgeons with an innovative tool to more closely create a natural breast in both shape and softness.