The FDA previously told manufacturers who wanted the ban lifted to provide long-term data on implant breakage and the consequences of silicone leaking into women's bodies. But Mentor's main study tracked implant recipients for only three years.

In late July, and following an April advisory panel vote in favor of Mentor's application, the FDA issued something called an "approvable letter." This was widely interpreted as approval subject to a number of undisclosed conditions.

On Tuesday, opponents sought to roll back the progress toward making silicone implants widely available in the United States for the first time since health and safety concerns led to a near-total ban in 1992.

Consumer advocates asked Congress to investigate the FDA's decision, claiming the agency is violating its own safety standards by not requiring more data on the long-term durability of the implants.

And a dozen women's and health groups urged the FDA to release findings of a late 1990s criminal investigation of Mentor.

Mentor Criminal Investigation 'Old News'

The company itself has dismissed the latest offensive as "old news."

President and Chief Executive Officer Josh Levine says these groups are again raising unfounded allegations from a lawsuit that was dismissed after the court reviewed all the facts and evidence.

"FDA conducted an investigation that we believe included these allegations and closed the file with no action taken," he said in a statement. "Mentor's Texas manufacturing facility has been audited by FDA and other international regulatory agencies annually since 1999.

"The FDA and its advisory panel rigorously and objectively reviewed Mentor's data and related science. We remain confident this scientific process will not be complicated by old accusations from parties with agendas that go well beyond the safety and efficacy of these products."

Consumer advocates say the FDA had previously told manufacturers to provide long-term data on implant breakage and the consequences of silicone leaking into women's bodies if they wanted the ban lifted.

But they say the FDA's step toward approval last month comes even though Mentor's main study tracked implant recipients for only three years.

FDA spokeswoman Julie Zawisza said that last year's advice to manufacturers about long-term data was not mandatory.

Allegations of False Reporting

Although major studies have failed to link implants to chronic diseases, questions persist over rupture rates and the health effects of leaking silicone. For more than a decade, American women have mostly been restricted to saline-filled implants, though the makers, Mentor and rival Inamed Corp., are selling silicone gel-filled versions overseas.

Also Tuesday, the National Organization for Women and a dozen other women's and health groups urged the FDA to release findings of its criminal investigation of Mentor in the late 1990s, to settle concerns that implant problems were hidden.

Allegations of false reporting surfaced through a 2003 civil court case and were made by people who had not worked at Mentor since at least 1998. For four years, between 1998 and 2002, the FDA investigated the claims but took no action against Mentor, which denied underreporting problems.

Regarding that probe, the FDA's Ms. Zawisza said some of agency's findings are releasable and the FDA is processing requests for them.