The standard implant in the United States has been saline filled, ever since the FDA moratorium on silicone gel filled breast implants in 1992. The type of implants that were available before the ban are available today as part of an "adjunct study," which is open to patients with congenital deformities or having a revision for particular reasons.

What distinguishes cohesive implants is that the silicone gel is firmer, essentially a soft solid. If a cohesive implant is cut in half, there is no gross movement of gel, and the implant maintains its shape.

The way these are made is that the company uses more "crosslinker" in the making of the implant. The ingredients are the same, but with more crosslinker added, it makes the gel firmer.
The term "cohesive" has been bastardized in recent years. Cohesive breast implants implies form stability, or form retention. That means that in any position, the implant maintains its shape. That is an important distinction, because it means that the shell should not fold, and that it will maintain a particular shape.

Unfortunately, given the recent media attention to cohesive implants, many are using the term to describe "regular" silicone gel implants. Technically, they are correct; all silicone gel is cohesive to some degree. But the term cohesive has always meant form stability, and when patients ask for cohesive gel, it is because they are looking for an implant with those particular characteristics of durability and shape retention. Hopefully, the terminology will be clarified in the coming years.

Which Surgeons Can Use Cohesive Gel Implants In The United States?
Each of the three studies has a group of only several dozen surgeons that are allowed to order the implants and implant them. Surgical expertise and a commitment to careful patient follow-up were the criteria the manufacturers used to select the surgeons that they would have implant their implants. Dr. Teitelbaum is the only surgeon in California (and if not the only, one of the very few in the entire nation) to have been asked by all three manufacturers to participate in their clinical trials

Which Patients Can Receive Cohesive Gel Implants In The United States?
The trials are open to patients seeking a first time augmentation, a revision of a breast augmentation, or breast reconstruction following mastectomy. Patients with certain medical problems cannot participate. Please see the enrollment specifications for each of the implants listed below. In addition to the objective medical issues, patients must be committed and willing to participate for a full ten years of follow-up to be considered for the study. Patients must be in the immediate geographic vicinity of the implanting surgeon in order to facilitate this follow-up.

Why Are Cohesive Gel Implants Anatomically Shaped?
A breast projects more at the bottom than at the top. Therefore, it makes sense for an implant to be shaped that way. And the thinner an implant is at the top, the more gradually and naturally it will feather into the upper chest, making itself less conspicuous. Without a cohesive, form stable filler, there is little point in making shape into an implant, as the implant will ultimately lose the shape. But with a form stable filler, the shape will be maintained.

Are There Round Cohesive Gel Implants?
Form stable round cohesive gel implants are available in Europe, but not in the United States. There is actually very little use for them. If you look at an implant lying on its side on a table, it looks much like an M&M. But when it is held upright, the upper pole gradually collapses. It is that upper collapse that allows those implants to look natural (though it is doing so at the risk of folds on the implant shell.) A true cohesive round does not do that. By maintaining that M&M shape when vertical, it creates a dome-like, relatively top-protruding shape.

However, cohesivity is not a black and white issue; there is an endless continuum in cohesive gel from very liquidy to very solid. On Silimed's cohesive clinical trial, there are 4 different round gel options. These are more cohesive than implants made in the past, and can be considered cohesive, but they are not as cohesive as their anatomically shaped cohesive gel implants or the anatomic cohesive implants by Mentor or Inamed. They fold less than gel implants of the past, but they are not quite form stable, in terms of their ability to resist folds or predictably maintain a shape.

Do Cohesive Gel Implants Come With A Smooth And A Textured Surface?
All anatomic (a.k.a. teardrop) shaped implants are textured, as the texturing increases friction and helps keep them from rotating. Since a teardrop implant is different at the bottom than the top, it is important that it maintains its position.
The Silimed round implants come in both smooth and textured surface, but remember that while relatively more cohesive than most other silicone gel implants, they are not form stable like their anatomically shaped cousins.

What Happens If A Cohesive Gel Implant Ruptures?
We do not really know, because there is so little experience with this. At the time of writing this, there is report of a single rupture in a series of several thousand in Sweden.
If it did happen, however, one would imagine that the gel, being relatively stiff and solid, would not migrate in any significant amount. Since it has the consistency of a gummy bear, the gel would presumably stay in place. Microscopic migration of gel would presumably occur, and this can even happen to some extent through an intact shell. This is a subject of ongoing investigation, and more research will be needed to answer this question.

How Would You Know If A Cohesive Gel Implant Has Leaked?
Given the gummy bear nature of the filler of these implants, it is likely that it would be difficult to tell if they ruptured. Perhaps it might be detected by mammogram or MRI.
When any implant is placed in the body, the body forms a capsule around the implant. If a cohesive implant were to leak, it would probably just stay within the capsule. The capsule might thicken, and a patient may notice a difference in the feel of the breast. But it is also possible that there might be no change at all.
The important point, however, is that silicone gel has not been linked with any health problem, so even if there were a shell disruption, it should not prove to be of any medical problem.