The object inserted is a prosthesis, that is, a foreign substance. The development of technique has been in part surgical, how to augment the breast with the least evidence it has been done, but also technological, how to leave foreign material in the body with no ill effects, short or long term.
The material contained in the saline implant is essentially innocuous, provided it is sterile. The saline is the body’s own fluid, and should the prosthesis leak or burst, the saline will do no harm, and saline filled prostheses have been in use in the USA since the '80’s. The concern then is the bag that contains the saline.
The saline containing bag has the advantage that it can be inserted uninflated through a minimal incision, and then filled through a self-sealing valve when in place. According to the patient’s preferences and the surgeon’s intentions, the shape of the prosthesis can be selected from a flattened sphere, a teardrop shape, or round; size is also a selectable decision.
The bag itself is made of rubberized silicone, called room temperature vulcanized (RTV) silicone elastomer, a material developed in the early 40’s by Corning Glass and General Electric for insulating electric motors. It has to pass the FDA requirements for implanting into the human body. No material exists that cannot be damaged, and although the bag is tough and deformable, it can be damaged at insertion, by subsequent rough handling, or either the bag or the valve may fail after a period of time. If failure should occur, the shape of the breast will be altered but there will be no untoward local reaction to the saline.
When in place, some patients have reported a sensation of “sloshing water” with movement, which is probably exactly what does happen; other patients, or their partners, report an unnatural hard feeling to the breast.
There is no such thing as an operation which does not have a potential for complications. The natural reaction of the body to any foreign material is to wall it off with fibrous (scar) tissue. An implanted prosthesis is liable to this reaction and to become tightly encapsulated by scar. This may be painful and may cause cosmetic distortion. Treatment is possible, though not always acceptable, by simple manual compression to break the capsule – it might also break the prosthesis! The alternative is an open operation to incise the capsule (capsulotomy) and/or remove/replace the prosthesis.