Marta:

Surgeons and patients share a desire for long-lasting breast implants, but the facts are that they are temporary devices.  They move with each movement of your body, and we want them to do that.  They undergo pressure, rubbing, etc within your body.  This cannot be expected to go on forever without wear and tear on the device.

Implants from Allergan and Mentor, whether filled with saline or silicone gel eventually will need replacement in most women.

Choose your plastic surgeon carefully and discuss your concerns with him or her.