What “second generation” means
1970s breast implant technology was an attempt to correct a problem with many first-generation silicone gel devices: they could feel firm and were associated with a hard capsule around the breast. Manufacturers changed the two components that most directly affected feel. The silicone elastomer shell became thinner and more flexible, while the filler became softer and less viscous. Many designs also removed the posterior Dacron fixation patches used in earlier implants. The intended result was a breast implant that felt less rigid and behaved more naturally.
That objective was reasonable, but the design changed the balance of risks. A thin shell could allow microscopic silicone molecules to pass through even when the implant still appeared intact. This later became known as silicone gel bleed or bleed-through. The less cohesive filler could spread more readily if the shell failed. Explant studies also found high rates of leakage and rupture in many late-1970s and early-1980s devices. The historical lesson is not that every change was wrong; it is that softness, containment and fatigue strength have to be considered together.
Why the generation label needs a caveat
“Second generation” is a retrospective engineering and clinical label, not the name of one worldwide product with one exact specification. Historical reviews commonly place first-generation implants in the early 1960s through about 1972, and second-generation implants from approximately 1972 through the mid-1980s. Dates differed by manufacturer and country, and product lines overlapped. Some changes were gradual rather than introduced on one universal date.
A date in an old medical record therefore cannot identify the exact shell, gel formulation, manufacturer, model or manufacturing lot. The generation label is useful for describing the broad direction of design development, but an implant card or operative report is more informative for an individual patient. The evidence discussed here concerns silicone gel-filled implants, mainly in cosmetic augmentation cohorts, although some explant series included reconstruction or mixed indications. Those populations should not be treated as interchangeable.
Why the shell became thinner
Many early silicone gel implants used a relatively thick elastomer shell and a firmer gel. Early models also used Dacron patches on the back to help with positioning. These features had practical advantages, but they could contribute to stiffness, a conspicuous implant feel and local stress. A patch could become a focal point for irritation or shell damage. The second-generation response was a thinner, more compliant, often seamless shell without the posterior fixation patch.
The proposed benefit was immediate and understandable. A thinner shell could flex more easily and make the filler, rather than a rigid envelope, determine the contour. Removing the patch eliminated a local reinforced interface that could be associated with rupture. One historical review gives approximately 0.13 mm for a representative 1970s Dow Corning design, while other reviews describe different measurements for different models. The reliable conclusion is directional: these shells were thinner than many earlier devices, not that every second-generation shell had exactly the same thickness.
The shell, however, is more than a wrapper. It is also a barrier and a fatigue-resistant membrane. With less material, there may be less reserve against folds, abrasion, surgical handling and repeated loading. A breast implant moves with the body and may be compressed by the capsule, chest wall, muscle or external pressure. Repeated folding can concentrate stress at a small area. A local defect can eventually become a leak or a full-thickness tear even while most of the shell remains intact.
Why the filler became softer and less viscous
Silicone gel is a family of materials rather than one uniform substance. Its feel and flow depend on the molecular components, cross-linking and viscosity. Second-generation filler was softer and less cohesive than the firmer gel used in many first-generation devices. Historical literature describes a representative formulation as containing mostly low-molecular-weight chains, often summarised as approximately 80% low-molecular-weight components and 20% high-molecular-weight components. Exact formulations varied, so this ratio should not be applied to every implant sold during the decade.
The intended advantage was a more natural feel. A soft filler could deform under the patient’s tissue and hand pressure instead of behaving like a firm defined object. For surgeons and patients who had experienced the firmness of earlier devices, this was a meaningful improvement in the short term.
The trade-off was containment. Low viscosity and low cohesion make a filler more mobile. If the shell tears, the gel can escape and distribute through the implant pocket more easily than a later form-stable or highly cohesive gel. Even without a visible tear, small silicone molecules can diffuse through the elastomer. This is gel bleed-through: microscopic movement across an apparently intact shell, distinct from a complete rupture.
Historical terminology is not always consistent. Bleed-through describes microscopic diffusion through the shell. Leakage may describe loss of filler through a defect without a complete disruption. Rupture means a structural tear or hole in the shell. If the surrounding fibrous capsule remains intact, the event is generally described as intracapsular rupture; if both shell and capsule are disrupted, silicone may reach breast tissue in an extracapsular rupture. The National Academies’ review stressed that gel-fluid diffusion and rupture are different events.
The first concern: silicone bleed from an intact implant
In a 1978 clinical report, Barker, Retsky and Schultz presented evidence that silicone could pass from intact bag-gel implants and be found in the surrounding capsule after extensive sampling. They also observed that the amount varied between individual implants. This did not show that every patient would develop a clinically important complication, but it established that an apparently intact shell was not necessarily an absolute barrier to every silicone component.
Bleed-through could be relevant to the capsule’s appearance and biology. Silicone particles and fluid components could be taken up by macrophages or become distributed in capsular tissue. In some reports, silicone was identified in nearby tissues or regional lymph nodes. These observations are not the same as proof of a systemic disease, and historical studies differed in sampling, definitions and clinical follow-up. The most defensible conclusion is narrower: the thin shell and mobile filler made microscopic diffusion a recognised device-design issue.
The second concern: leakage and rupture over time
As more second-generation implants remained in place for years, reports of leakage and rupture accumulated. A retrospective series by de Camara and colleagues reviewed 51 implants removed from 31 women between 1987 and 1990. Twenty-seven were ruptured, seven were leaking and 17 were in good condition. All implants older than ten years in that selected series were leaking or ruptured, and the number of intact implants declined with increasing duration.
The most frequently quoted figures come from Peters, Smith and Lugowski’s analysis of 352 explanted silicone gel implants removed from 239 patients between 1981 and 1995. The series included 302 second-generation implants. Its survival curve suggested that failures by leakage or rupture began after about four years, reached 40% by six years and reached 95% by twelve years in that cohort. Of 171 second-generation implants removed between 1991 and 1995, 77% had failed.
These figures are important historical evidence, but they are not a universal timetable. The implants were removed from patients who had already entered a surgical or specialist pathway. Symptoms, firmness, suspected failure, asymmetry or another problem may have made removal more likely. An explant cohort can therefore over-represent failure compared with all patients who received an implant. Manufacturer, model, lot, implant duration, surgical pocket and the reason for removal also affect the result.
Other evidence showed the same general direction with additional variation. Peters’ earlier clinical series found that integrity declined with time and was not explained simply by the severity of capsular contracture. A later review of 478 consecutively explanted implants found that late-1970s and early-1980s, second-generation devices were more likely to have lost integrity. It also reported an association with subpectoral placement, but that finding may reflect mechanical and patient-selection factors; it does not prove that pocket position alone caused failure.
Why a softer design could create shape concerns
Shape concerns were not one single defect. They arose from the interaction between a flexible shell, mobile filler, capsule and breast tissue.
First, a compliant shell could form folds. A fold is not automatically a complication, but repeated folding can concentrate stress and make wrinkling or rippling visible or palpable, particularly where the tissue covering the implant is thin. The contour may become more dependent on the surrounding soft tissue and on how the implant sits in the pocket.
Second, low-viscosity gel could redistribute after a shell failure. If the filler no longer remained inside the shell, it could move within the pocket or capsule and, after capsule disruption, into breast tissue. This could be associated with firmness, nodules, inflammation, asymmetry or a changed contour. A visible shape change was not necessarily caused by gel flow alone; rupture, capsule reaction, tissue stretching and time could all contribute.
Third, softer filler did not eliminate capsular contracture. A contracting capsule could make a soft implant feel hard, distort the breast and apply extra stress to folds in the shell. The 1970s design therefore did not simply “solve” contracture. It addressed some material contributors to firmness while leaving the biological response to a foreign device unresolved.
Fourth, removing a fixation patch changed how the device depended on the pocket and surrounding tissue for stability. A patch had its own disadvantages, but a patch-free implant also relied more on pocket geometry, tissue support and surgical handling. Displacement, a changed breast fold or asymmetry could affect shape independently of bleed or rupture.
For a current plain-language explanation of how filler, coverage and position influence visible or palpable folds, see the practical guide to breast implant rippling. That practical page translates the design variables into patient questions; it does not replace the historical evidence in this article.
How these problems redirected implant development
The experience of second-generation devices helped redirect development in the 1980s. Manufacturers worked toward stronger or multilayered elastomer shells, barrier layers and more cohesive gels. The aim was to reduce movement of low-molecular-weight silicone through the shell and improve resistance to tearing. Historical reviews describe a representative third-generation direction with a thicker shell reinforced with silica and a lower-bleed design.
This is not a simple story in which every later generation was universally superior. Surface, shape, gel cohesivity, pocket conditions and surgical technique each have their own risks and evidence. The 1970s are best understood as an engineering lesson: a more natural feel is valuable, but so are containment, fatigue resistance and the ability to monitor a device over time.
What this history can — and cannot — tell us today
The strongest conclusion is about design trade-offs. Compared with many early thick-shell, firmer-gel implants, second-generation devices pursued a softer feel through a thinner, more compliant shell, less viscous filler and, in many models, removal of Dacron patches. The same features reduced the margin for containment and mechanical durability. Clinical reports and explant studies support higher rates of gel bleed, leakage and rupture in many devices from this era.
The weaker conclusion would be that every implant made in the 1970s failed, that every patient developed a clinically important complication, or that historical failure figures predict modern implant performance. The studies are heterogeneous, retrospective and often based on patients selected for explantation. Historical papers also combined endpoints differently, with “failure” sometimes including both leak and rupture.
Current devices should not be judged from the failure rates of historical models, and current devices should not be described as risk-free because they use a different shell or filler. The U.S. Food and Drug Administration’s current patient information states that breast implants are not lifetime devices and that product-specific labeling matters. That is not a retrospective safety certificate for 1970s implants; it is a reminder that device identity and long-term follow-up are important.
Someone who may still have an older implant should gather the implant card, operative report and records showing manufacturer, model and date. New firmness, swelling, a mass, pain, asymmetry or a sudden change in size warrants assessment by a qualified clinician. Symptoms alone cannot identify bleed-through or rupture. Depending on the clinical question, examination, imaging or surgery may be needed.
For readers comparing filler and appearance questions rather than studying history, the practical silicone vs saline breast implant guide explains how filler, tissue coverage and rupture presentation are discussed today. The guide to how long breast implants last adds practical context about records, monitoring and later decisions. The current breast augmentation operation information provides procedural context; none of these pages is evidence that a particular product, volume or shape is suitable for an individual patient.
Conclusion
Second-generation breast implants emerged from a genuine attempt to make augmentation softer and more natural-feeling. The thinner shell, low-viscosity gel and patch-free construction changed the physical relationship between implant and tissue. They also created new failure modes: microscopic silicone bleed through the shell, a less contained filler after rupture, greater vulnerability to folds and long-term fatigue, and shape changes influenced by the capsule and surrounding breast.
The history does not support a slogan that one generation was simply good and the next simply bad. It supports a more useful principle: an implant must be assessed as a complete system, and a short-term improvement in feel does not prove long-term durability. Historical device era, exact product records, symptoms, examination and evidence quality all matter.