"Though saline breast implants are carefully pre-inspected, and made of strong and durable silicone polymers, they cannot last indefinitely. To the benefit of the breast implant recipient, all breast implants currently available in the US are backed by a lifetime manufacturers' replacement warranty, and in the first 5 years after placement, Mentor implants provide for a $1200 reimbursement toward the OR and anesthesia costs of implant replacement. Failure causes are numerous, but certain general facts are known. Thinner walled implants seem to be more long-lasting than thicker walled implants. Smooth breast implants tend to last longer than any textured wall implants (they are also thick-walled). Situations where there is excessive implant folding or wrinkling, as in placement in a constricted (too-small) pocket, lead to failure by causing stress fracturing of the silicone polymer shell at the fold points, and thus the potential benefit of vertically oversized pocket development and massage pocket maintenance. Implants which are filled below the least nominal volume for which they are rated tend to wrinkle and fail prematurely, as well."
That's taken from Dr. Dewire's website here in Virginia which points out some interesting tidbits. My doctor never told me all implants sold in the US are guaranteed!