April 11 (Bloomberg) -- Mentor Corp. and Inamed Corp.'s silicone breast implants may not be any safer than when U.S. regulators banned earlier devices 13 years ago, doctors and women's groups will tell government advisers today.

The testimony will be part of a three-day meeting of doctors and scientists who will vote on whether the Food and Drug Administration should lift restrictions on the implants. The FDA staff projected that there might be 22,500 cases a year of ruptured implants, which have been linked to connective tissue disorders and pain.

``If you buy a Chevy and there are more than 1 percent of vehicles that have a problem, the National Highway Traffic Safety Administration recalls the vehicle,'' said Edward Melmed, a plastic surgeon in Dallas, in a telephone interview April 8. ``We have a medical device that may fail up to 50 percent of the time. And how do you recall implants in a woman?''

The advisory committee is meeting as the FDA is under pressure from Congress over its monitoring of medical safety. Last week regulators asked Pfizer Inc. to withdraw its Bextra painkiller because of heart and skin risks, six months after Merck & Co. recalled the similar Vioxx pain drug over a link to heart attacks and strokes.

Inamed and Mentor, both based in Santa Barbara, California, said in their filings with the FDA that data they gathered showed their silicone implants are safe.

``What have the manufacturers done to prevent ruptures within 10 years?'' said Melmed, who specializes in removing implants. ``The question is what is an acceptable rate of failure of a device.''

The agency, which usually follows the advice of its panels, appointed a cancer surgeon who voted against resuming silicone breast implant sales in 2003 as chairman of this week's committee. The three-day meeting is in Gaithersburg, Maryland, about 25 miles from Washington.

The FDA has never approved a silicone breast implant. The devices are sold in the U.S. for use in research in women who have lost their breasts or have deformities. Silicone implants already were on the U.S. market in 1976 when the FDA was given authority to regulate medical devices. Companies at the time were allowed to continue selling products already on the market.

U.S. regulators banned most use of silicone implants in 1992 because the devices might cause connective-tissue diseases such as rheumatoid arthritis. These conditions occur when the body's immune system goes awry and attacks its own tissue. Leaking implants allow silicone gel to move to the area surrounding the breast and have been found in lymph nodes.

In 1998, Dow Corning Corp. agreed to pay as much as $3.2 billion over 16 years to settle claims of more than 300,000 women who said they were harmed by the company's silicone implants. The next year, the U.S. Institute of Medicine issued a report that found no connection between silicone breast implants and connective-tissue diseases.

That didn't resolve doubts about whether a minority of women may develop such illnesses from silicone implants. FDA staff doctors in 2000 published research suggesting a potential connection with fibromyalgia, a syndrome characterized by chronic pain in muscles and around joints.

The FDA continued to allow sales of silicone implants for women who qualify for studies, such as those who need breast reconstruction after cancer treatment. Implants for cosmetic use have been filled with a saline solution. Inamed sells saline implants for $300 to $400 each, and silicone for use in studies for about twice as much. Silicone has a more natural feel, Mentor Chief Executive Joshua Levine said in a March interview.

U.S. sales of implants to enlarge healthy breasts, now a $300 million annual market, may rise by $60 million following an end to the ban on silicone devices, said Juan Noble, an Oppenheimer & Co. analyst in New York.

Mentor shares rose 48 cents to $34.19 April 8 in New York Stock Exchange composite trading. They have risen 1.3 percent this year. Inamed shares rose 69 cents to $65.59 in Nasdaq Stock Market composite trading. Medicis Pharmaceutical Corp., based in Scottsdale, Arizona, said March 21 that it intends to buy Inamed for about $2.8 billion in cash and stock.

``Our submission includes clinical information that recorded a three-year overall patient satisfaction of 97.2 percent, and an overall rupture rate of confirmed and suspected ruptures of 1.4 percent,'' Mentor's Levine said in an April e-mail.

FDA staff doctors found the Mentor and Inamed data on ruptures to be of ``limited'' value, according to review documents posted on the agency's Web site. In the Inamed review, the FDA staff estimated the probability of implants rupturing over 10 years at anywhere from 21 percent to 74 percent. For women getting implants to replace breasts, as with cancer patients, the rupture rate at 10 years may be as high as 93 percent, by one FDA calculation.

The FDA staff then referred to published Danish research as a guide for estimating implant failure rates. The Danish studies found about nine ruptures for each 100 implants. The American Society of Plastic Surgery estimates that about 250,000 women had implants in 2003. Based on those figures, the FDA calculated that about half of the women seeking implants for healthy breasts would choose silicone and that there would be ``at least 22,500 implant ruptures per year.''

Mentor and Inamed haven't published rupture data in medical journals, said Leroy Young, a St. Louis surgeon who works with saline and silicone implants. Doctors tend to trust published research most. When journals receive potential articles, they send them out for review by researchers who know the subject of the paper well.

``That is a flaw in this process,'' Young said in a telephone interview. ``What the public gets is filtered data, as opposed to something that goes through a peer-review process, where all the warts and bumps have been pointed out.''