Implants may be categorized based on filler, shape, and size. All breast implants have a silicone shell as the outer layer. They may be filled with either saline (salt water) or silicone. Some patients prefer silicone implants for a more natural feel vs. saline implants, however some studies have shown no difference when they are placed under the pectoralis major muscle. There are many generations of silicone implants. Current silicone implants are made of cohesive gel, which is form stable. This means there is lower risk of bleeding through the implant shell and if implant failure or rupture occurs, it is contained within the implant pocket.nImplant shape may either be round (most commonly) or anatomic (tear-drop shaped). The concern regarding anatomic implants is that they may shift in the pocket, which could lead to secondary aesthetic concerns.