The U.S. Food and Drug Administration (FDA) recently approved the use of a third brand of silicone-gel breast implants, this one manufactured by California-based Sientra. Allergan and Mentor are the other two FDA-approved silicone-gel breast implant manufacturers.

Silicone gel-filled breast implants are medical devices implanted under the breast tissue or under the chest muscle for breast augmentation or reconstruction. These implants have a silicone outer shell that is filled with silicone gel. They come in different sizes and have either smooth or textured shells.

"We are elated to receive FDA approval of our flagship portfolio of silicone breast implants," said Hani Zeini, Sientra founder and CEO. "This represents two significant milestones. Namely, for the first time in 20 years, Sientra has successfully broken the existing duopoly in the U.S. by offering surgeons and patients a new choice. And today, Sientra becomes the first and only company in the U.S. to provide a full portfolio of commercially-available breast implants, including shaped implants in addition to standard round implants."

Until now, the only approved silicone-gel breast implants in the U.S. market have been round. With the approval of Sientra's implants, patients can opt for a shaped implant, which had only been available with saline implants up until now. Some surgeons believe shaped implants look more natural, as they are shaped more like a natural breast.

In addition, the Sientra implants come in different sizes and have either smooth or textured shells.

The FDA approval was based on three years of clinical trials involving 1,788 participants. The company is also required to continue following these patients for an additional seven years as well as conduct a separate, 10-year study involving nearly 5,000 women to collect information on long-term local complications such as capsular contracture, as well as less common disease outcomes, such as rheumatoid arthritis and breast and lung cancer.

According to the American Society for Aesthetic Plastic Surgery (ASAPS), breast augmentation surgery remains one of the most popular plastic surgeries offered by doctors. In 2011, it was the second most popular with 316,848 individuals undergoing the procedure.

Common reasons women choose to undergo this surgery include the perception of underdeveloped breasts, differences in the sizes of the breasts or changes after pregnancy or breast feeding. The procedure, which is used to improve breast shape and size, can give a woman more proportional shape and may improve self-esteem.

Several factors must be considered when deciding the size, type and location of a breast implant, including an individual's goals for breast enhancement, their existing body frame, mass and breast tissue. A licensed, board-certified plastic surgeon can help make recommendations for breast implants and other cosmetic procedures.