A breast implant is comprised of a silicone elastomer shell, or envelope, filled with either saline or silicone.
Both implants are intentionally under filled. This is intended to allow the implant to move like breast tissue and assume natural shapes with different changes of position. When the patient stands up silicone or saline will concentrate more toward the bottom of the implant assuming more of a “teardrop” shape. When the patient lies down it flattens out to some degree resembling a breast in the recumbent position.
Due to the fact that they are under filled, there are wrinkles and folds in the implant. The folds of a silicone implant are blunter compared to the saline folds. The saline folds are sharper and consequently more palpable and visible.
When the implant is placed, the body will naturally form a lining around the implant called a capsule. This is a natural barrier created to separate the implant from the rest of the body. In the event of a leak, the silicone is normally contained within the capsule. Because it is contained within the capsule the size and the shape of the breast may not change very much. When a saline implant leaks, the salt water is absorbed into the body, and the breast dramatically loses volume. If a silicone implant and a saline implant are placed side to side and both punctured with a needle, the saline implant would deflate in the first 24 hours whereas a silicone implant may not change at all. Consequently it’s reasonable to assume that a silicone implant will last longer.
The FDA has approved the use of saline implants for anyone 18 years of age or older. Silicone implants have been approved for anyone 22 years of age or older.