FRIDAY, July 29 (HealthDay News) — After a 13-year moratorium, silicone gel-filled breast implants are making their way back to the U.S. market.

Thursday night, the U.S. Food and Drug Administration moved one step closer to this end by issuing an “approvable letter” for Mentor Corp.’s application to reintroduce the product.

Reaction was swift and urgent, with calls for caution coming even from a bipartisan group of female U.S. senators, including Dianne Feinstein (D-Calif.), Olympia Snowe (R-Maine) and Hillary Clinton (D-N.Y.).

The nine senators sent a letter to FDA Commissioner Lester Crawford urging the agency to consider women’s health safety in its final decision on the implants.

Because of flaws in the basic research, CNN reported, the senators said they were “extremely concerned that the risks of this device are far disproportionate to the benefit that a woman undergoing breast augmentation would realize.”

The letter also noted differences between saline and silicone implants, stating that silicone implants “bear greater risk.” The FDA was urged to note the additional distinction between using implants for reconstruction following cancer surgery and implants for augmentation.

Post-marketing companies conditions meant to address safety concerns “have proven to be ineffective or unenforceable,” the letter concluded.

The other senators signing the letter were Kay Bailey Hutchison (R-Texas), Barbara Boxer (D-Calif.), Mary Landrieu (D-La.), Debbie Stabenow (D-Mich.), Blanche Lincoln (D-Ark.) and Barbara Mikulski (D-Md.).

Other reactions were mixed.

Diane Zuckerman, president of the National Research Center for Women & Families, criticized the decision as “pathetic science” and “bad politics” while at the same time urging people “not too make a big deal of this.”

“This is a step in a process, not a final decision,” she said. “I would say a stumble in the wrong direction, because I think it’s illogical and really undermines the credibility of the FDA at a time when their credibility is not too high to start with. I think it’s politically an error for Dr. [Lester] Crawford [head of the FDA], who’s just been confirmed, to proceed, I think, recklessly in this direction.”

Zuckerman stressed that her organization is not against silicone implants or any other implants. “We’re a critic of unsafe medical implants,” she emphasized. “We just want some safe implants whatever they’re made of.”

Dr. Richard A. D’Amico, chairman of the breast implant task force of the American Society of Plastic Surgeons and the American Society of Aesthetic Plastic Surgery, said, “The FDA decision really follows as a logical outcome of the science on these devices. They’re the most studied medical device and the data supports their use.”

D’Amico speculated that, depending on conditions requested of Mentor by the FDA, things could get going by the end of the year. “The plastic surgery societies are fully prepared to teach the educational component the FDA may require,” he said. “There will probably be other conditions, including a breast implant registry and we’re very supportive of that. That would really allow thorough postmarket surveillance. Plastic surgeons are ready to go now. We’re just waiting for FDA conditions.”

Dr. Nolan Karp, associate professor of plastic surgery at New York University School of Medicine, said, “I think it’s about time. The companies, particularly Mentor, did what the FDA asked. What Mentor has is a more cohesive gel implant so if it ruptures, the gel is much less likely to come out.”

The letter sent from the FDA to Mentor Corp. spells out certain conditions the company must meet to receive final FDA approval to market the implants