Saline breast implants, unlike silicone implants, don't come pre-filled. They are filled during the breast augmentation surgery. Knowing the sweet spot for fill will help you not to overfill or underfill your saline breast implants, lowering your risk of rippling and implant rupture.
Overfilled saline breast implants
Saline implants come in a wide range of sizes, and all of them have a minimum and maximum fill amount that is recommended by the manufacturer. For example: The Mentor Style 1600 smooth round 300cc implant can be filled to (f/t) 325cc. 325cc is the maximum amount of cc's recommended by the manufacturer, and 300cc is the minimum fill amount recommended for that particular implant size.
A breast implant filled passed the point of the manufacturer recommendation is considered "overfill." Overfilling (depending on the amount) makes the implant feel firmer, but doesn't provide any distinguishable size difference.
It’s very important to remember that overfilling the breast implant gives the implant manufacturer the right to void the warranty in the event of a rupture. This doesn't mean that they will void it, but it does give them that option.
Overfilling may also increase your risk of having visible and/or palpable ripples.
Underfilling saline breast implants
If the implant is not filled to the minimum recommendation, it can get folds in it, which can jeopardize the integrity of the implant. The constant rubbing of the fold can lead to rupture. Visible ripples are also more common in implants that are not filled to the minimum recommended amount, depending on the amount of breast tissue you start with.
In other words, if you have a Mentor Style 1600 300cc size implant, you will want it filled to a minimum of 300cc, nothing less, and preferably no more than 325cc, which is the optimum fill level recommended by Mentor.
Underfilling may also void the manufacturer's warranty.
Updated August 2016