Shares of

Mentor Corp

(MNT)

surged Thursday after a federal advisory panel unexpectedly recommended its silicone-gel breast implant for marketing clearance. The shares gained $3.47, or 10%, to $38.80 Thursday.

Shares of

Inamed

(IMDC)

, meanwhile, continued to fall, two days after its implants failed to get the panel's blessing. Inamed fell $3.36, or 5.3%, to $60.15 Thursday, while shares of the company that is in the process of acquiring it,

Medicis

(MRX)

, fell 65 cents, or 2.4%, to $27.10.

If the Food and Drug Administration follows the lead of its advisory panel, the Mentor product would be the first silicone-gel implant approved for widespread use in the U.S. since 1992. The advisory committee voted 7-2 for the product Wednesday night.

The FDA usually follows the recommendations of its advisory panels, but it isn't bound by their suggestions. In October 2003, for example, an advisory panel endorsed an Inamed silicone-gel implant by a 9-6 vote; but the FDA voted against approving the device in January 2004. The FDA said the company didn't prove that the product would be safe over time.

Long-term safety was the key reason the advisory committee on Tuesday voted 5-4 against the latest Inamed application. Analysts who follow the two implant companies said they believed Inamed had a better chance of gaining advisory committee approval.

The advisory committee's decision on Wednesday sent Mentor's stock rising in after-hours trading. In regular trading, the stock closed up 77 cents, or 2.2%, to $35.33. But after hours, the stock gained another $3.87, or 11%.

Meanwhile, Inamed's stock suffered. In regular trading, it fell $2.90, or 4.4%, to $63.51. After hours, it lost another $3.21, or 5.1%.

The advisory panel attached an assortment of conditions to its recommendation, according to wire service reports. For example, it said Mentor could only sell the implants to board-certified plastic surgeons who complete special training, and to patients who sign documents showing they understand that the implants could rupture.

Mentor also must prepare a patient registry to assess the long-term results of the device and conduct a clinical study to track the implant rupture rate over 10 years.

Since 1992, the FDA has severely restricted silicone-gel implants to a few uses, such as breast reconstruction after a mastectomy and replacement of a ruptured silicone implant. Although silicone implants entered the U.S. market in 1962, the FDA didn't receive legal authority to regulate them until 1976.

Over the years, the FDA

strengthened its regulations to such a point that by 1992 manufacturers first had to show comprehensive, long-term safety data to support applications for new implants or to keep older ones on the market. As a result, silicone implants, which are sold in many countries, aren't available in the U.S. except in rare circumstances.

Saline-filled breast implants are sold in the U.S. for cosmetic surgery purposes. The implant industry and plastic surgeons have sought FDA approval of silicone implants, saying the new products are superior to past devices.

They argue that women should be given the opportunity to make an informed decision on a product that many say provides a more natural look and feel than saltwater-filled implants. Inamed and Mentor sell saline implants for cosmetic surgery use in the U.S.

The silicone-gel implant applications for Inamed and Mentor were criticized last week by FDA staff members, who issued reports saying the companies'

research was inadequate to prove long-term safety and to assess the rate of implant ruptures over time.