Why don't many doctors recommend saline implants anymore?

Thank you for your question.  Both saline and silicone implants are safe and effective.  They have similar silicone outer shells but the volume filler is different (saline vs silicone).  Many surgeons become proficient in submuscular saline augmentation during the 90's and early 2000's due to the moratorium on silicone gel filled implants from 1992-2006.  For many women with adequate breast tissue, saline implants were really not a problem, except for the progressive rupture rate with time (1.5-2% added each year).  For thin women however, visible wrinkling and rippling were a real concern, even with placement under the muscle.  Additionally, most women were not candidates for placement of their saline implants over the muscle (traditional method) because of the rippling/wrinkling.  In an effort to decrease these problems, the saline devices were filled to the maximum recommend fill volume or higher.  This decreases rippling but increases the hardness/firmness.   Once silicone gel implants returned for cosmetic use in 2006, most surgeons have switched the majority of their implants to silicone gel.  The reason:  they look and feel much more natural, with less wrinkling and rippling.  As a result, thin women had less visible issues and patients with more breast tissue have the option again of subglandular pocket placement.  The downside for silicone gel is the labeling from the FDA regarding MRI exams despite lack of prospective studies demonstrating an absolute need for MRI in an asymptomatic patient.   The one benefit of saline implants is their cost, they are cheaper.  In my practice, nearly every patient is offered silicone gel and it is hard to remember the last time I used a saline device.  Best to get a few opinions from board certified plastic surgeons if you are confused or unclear.  Good luck.  

I prefer silicone gel implants because of all the usual reasons- more natural look and feel and fewer ripples.  Saline filled implants feel firmer and drop down or to the side more frequently due to the "water hammer" effect.  This makes the breast look abnormal and requires surgery to fix.  The newly released Ideal Implant is a new type of saline implant.  It is FDA approved and available to a limited number of surgeons.  Reportedly, it has a more natural feel.

Short answer: Because saline implants can leak and deflate, requiring re-operation to replace. This occurs in as many as 10% of women who have saline implants, especially those that are textured or not (properly) overfilled. Saline implants also have a higher incidence of visible rippling, a less natural "feel," and move unnaturally (Baywatch coconuts, anyone?). But they are cheaper, and do generate more profit for the surgeon. Oops, wasn't supposed to let that "secret" out!
Longer answer:
In 1991, the FDA restricted the use of silicone gel implants in elective cosmetic breast enlargement surgery, and surgeons were "forced" to use saline implants. So those of us who operated back then have lots of experience with the pros and cons of saline implants.
When the FDA re-approved the use of silicone implants for elective first-time cosmetic breast augmentation patients in November, 2006, the majority of plastic surgeons switched back to (the newest cohesive) silicone gel  implants. Not 51%, but 85%! This is because silicone implants are softer, more natural, cannot "leak" or deflate, and despite the FDA's "recommendation," MRI scans every 2-3 years to look for "leak or unsuspected rupture" is nonsensical, since ALL silicone implants by all 3 USA implant manufacturers are now cohesive and cannot leak or deflate. Implant ruptures or manufacturer defects are exceedingly rare, and statistics you see regarding this are due, IMHO, to surgeon damage, not implant defect. Another dirty little "secret."
And, BTW, those MRI scans "recommended" by the FDA are wrong 21% of the time! Leading to unnecessary surgery in 1 in 5 patients! Older silicone implants could indeed "leak" or rupture, and MRI scans for older generations of silicone gel implants may be appropriate, but not for present-day implants!
So why do some surgeons still "push" saline over silicone? And continue to use "scare tactics" regarding silicone MRI scans or autoimmune illnesses (proven false, BTW)? Either they are "out of date" and stuck in the habit of saline implants . . . some surgeons believe change causes complications, and do things exactly the way they were trained many years ago. Others are motivated by the higher profit potential with saline, but of course they can't say that, so they discuss MRI scans and autoimmune illnesses. And let the patient "share" in the cost savings.
Silicone implants cost a bit more at first, but avoid later costs for re-operation to fix deflation. And, no, you DON'T need periodic MRI scans if you choose silicone. Honest. Read more in my Comprehensive Guide to Breast Augmentation by clicking on the web reference link below. Best wishes! Dr. Tholen