Silicone-filled Breast Implants. Silicone-filled breast implants are filled with a silicone gel. Over the years, the consistency of this silicone filling has changed. The first silicone breast implants were filled with a very thin, oily silicone. Currently, the silicone used in implants is a gel that is less likely to leak out of the shell if it ruptures. This gel is referred to as "cohesive." Some breast implants — called gummy bear breast implants — are even more cohesive, or "form-stable," and have the consistency of a gummy bear, thus the nickname.
Both saline-filled breast implants and silicone-filled implants have an outer shell composed of silicone elastomer. This shell is basically a flexible envelope that contains the implant filling. In the case of some anatomically shaped implants, the shell also gives the implants shape. Some models of implants have a "double lumen." This is an elastomer envelope inside of another elastomer envelope (sort of like double-bagging your groceries) which may reduce the risk of implant rupture.
The current lifetime risk of BIA-ALCL in the U.S. is unknown, but estimates have ranged between estimated to be between 1 in 70,000 to 1 in 500,000 women with breast implants according to MD Anderson. Certain geographic locations have demonstrated variable risks. For instance, a December 2016 update from the Therapeutic Goods Administration of Australia and New Zealand reported a risk of 1:1,000 to 1:10,000 for textured implants.". To date (2017), there has not been a case of BIAL reported where the patient had only implantation of smooth shell breast implants or a textured tissue expander that was exchanged for a smooth implant. The paucity of cases reported in Asian populations has raised the possibility that there may be a range of genetic susceptibility to the phenomena, or alternatively merely reflect differences in how cases are identified and reported.