Aesthetic medical device giant Allergan (NYSE:AGN) won FDA approval this week for a new generation of its Natrelle silicon gel-filled breast implants.

The new Natrelle 410 features a more anatomical shape that imitates the slope of the breast, providing an alternative from traditional round gel implants, the company noted. It’s also filled with a "highly cohesive silicone gel," which Allergan says will hold its shape over time while remaining soft to the touch.

The approval marks the 4th silicon breast implant approved for the U.S. market, alongside previous Allergan implants and those made by Johnson & Johnson (NYSE:JNJ) subsidiary Mentor and Sientra, which in March 2012 became the 3rd company with permission to sell breast implants in the U.S.

"The Natrelle 410 is the most-selected shaped gel implant in markets where the product is already available, such as Europe and Canada," Allergan president & CEO David Pyott said in prepared remarks. "We are pleased that the FDA has recognized the benefits and safety of the Natrelle 410, and has now made the product available as an additional option for women in the United States."

Like other breast implants on the U.S. market, the Natrelle 410 devices are prone to certain adverse results, such as tightening around the implant area, the potential need for implant revision or removal, implant asymmetry or infection.

The Natrelle 410 devices, however, are uniquely subject to a condition the FDA called "gel fracture," defined as fissures or cracks in the gel of some of the implants.

"It’s important to remember that breast implants are not lifetime devices," FDA Center for Devices & Radiological Health director Dr. Jeffrey Shuren said in prepared remarks. "Women should fully understand the risks associated with breast implants before considering augmentation or reconstruction surgery, and they should recognize that long-term monitoring is essential."

The Natrelle 410’s silicone filling features more cross-linking, resulting in a firmer gel, the clinical significant of which is not yet known, the FDA noted.

Allergan’s clinical trials of the Natrelle 410 did not compare the implant directly to other FDA-approved breast implants, so researchers were unable to speculate on how the devices might rate against those already on the market.

The federal watchdog agency granted its approval for the Natrelle 410 with conditions, requiring that Allergan conduct post-market studies to get a better sense of the long-term performance of the implants.

According the agency notice, the FDA has required Allergan to:

• "Continue to follow, for an additional five years, approximately 3,500 women who received the Natrelle 410 implants as part of the company’s continued access study;
• Conduct a 10-year study of more than 2,000 women receiving Natrelle 410 silicone gel-filled implants post-approval to collect information on long-term local complications (e.g., capsular contracture, reoperation, removal of implant, implant rupture) and less common potential disease outcomes (e.g., rheumatoid arthritis, breast and lung cancer, reproductive complications); 
• Conduct five case control studies to evaluate the possible association between the Natrelle 410 implants, as well as other silicone gel-filled breast implants, and five rare diseases—rare connective tissue disease, neurological disease, brain cancer, cervical/vulvar cancer and lymphoma;
• Evaluate women’s perceptions of the patient labeling; and
• Analyze the Natrelle 410 implants that are removed from patients and returned to the manufacturer."