GAITHERSBURG, Md. -- A federal advisory panel has recommended the creation of a nationwide database to follow women who have had silicone-gel breast implants for at least a decade after they had the surgery.

The two companies that manufacture silicone implants -- Allergan and Mentor -- are required to follow women who've had their implants for a number of FDA-mandated studies, but enrollment in those follow-up studies has been disappointing, and in some cases the number of women being followed is so small that FDA cannot definitely rule out a connection between implants and a rare disease, such as anaplastic large-cell lymphoma or connective tissue diseases.

The FDA's General and Plastic Surgery Devices Panel, which wrapped up a two-day meeting Wednesday afternoon, said that current data collection demands are too onerous. Both companies ask women who've received their implants to fill out a 25-plus page questionnaire every year following surgery. Not surprisingly, not many women do that.

In 2006, the FDA broke a 14-year moratorium on silicone implants by approving two new models, one made by Mentor and one by Allergan. The approval was controversial because critics of silicone implants said there wasn't enough evidence that the implants were safe in the long term.

To study how the implants held up longer-term, the FDA ordered Mentor and Allergan to perform an array of follow-up studies -- some of which won't end until 2016. The studies involve 80,000 implant recipients -- 40,000 for each of the two brands -- who will be followed for a decade.

But so far, Allergan has mustered only about a 60% follow-up rate after two years for its studies -- far short of the goal of 93% -- and only one in four patients who received a Mentor implant were followed up after two years.

Creating a national database that isn't tied to any particular company could help the FDA more easily collect data on how safe and effective breast implants are many years after they're implanted. Having all women who have received breast implants, either for cosmetic or reconstructive purposes, in one place could allow researchers to select samples from the registry to answer questions such as "What percentage of silicone implants leak?" and "How long is the lifespan of a breast implant?"

FDA reviewers recently said that complications such as capsule contracture are common and the implants often needed revision within 10 years.

Meanwhile, the companies will likely still be required to continue collecting follow-up data. William Maisel, MD, chief scientist and deputy director for the FDA's Center for Devices and Radiological Health, told reporters after the meeting that he thinks the companies can achieve higher follow-up rates.

For example, a major tracking registry exists for cardiovascular implantable devices. It's run by the American College of Cardiology and tracks millions of heart devices from stents to pacemakers. Part of the success of that database is that doctors are required to enroll their patients in the registry or face not getting reimbursed by Medicare, Maisel said.

While the idea of a breast implant registry is just in its beginning stages, it could potentially link some reimbursement to registration or else incentivize doctors in some other way to get their patients enrolled and to keep them in the study so longitudinal data could be obtained.

Patients may need an incentive too, to encourage them to go to follow-up doctor's appointments, fill out questionnaires, and participate in focus groups.

"You can have the most well-meaning company, but if patient doesn't want to participate, the study won't work," Maisel said.

The panel, which took no formal votes, also recommended bringing a group of stakeholders -- doctors' groups, patient groups and governmental organizations -- together to discuss how to encourage enrollment in a large registry and what specific data should be collected.

The FDA also recommends that women with implants get a breast MRI three years after receiving the implants and every two years thereafter to screen for ruptures -- even if the woman is having no problems with her implants -- but rates of the screening MRIs also have been low. Not all insurance companies cover MRIs if there's no physically apparent problem, and most women aren't willing to pay for an MRI out-of-pocket.

The panel recommended not requiring future post-approval studies to suggest or mandate that women who seem to be having no issues with their implant undergo an MRI.

However, Maisel said the FDA still thinks MRI is the best way to detect if an implant has ruptured.

"We continue to believe that MRI is the gold standard for diagnoses breast implant rupture, in particular silent rupture," said Maisel, referring to a leak or tear in the implant that is undetected by the woman.

While the FDA would like to better track health outcomes in women who have received silicone breast implants, it doesn't expect longer-term data to reveal that the devices are unsafe.

"Based on the totality of information on silicone gel breast implants, the FDA continues to believe that the currently approved devices are safe and effective for their intended use," Maisel said. "There are significant complication rates associated with silicone gel breast implants, but we believe that the benefits and risks are sufficiently well understood that they should remain on the market."

Most of the five to 10 million women worldwide who have breast implants are satisfied with them, according to data from the FDA.

About 297,000 breast augmentation procedures and 90,000 reconstructions with implants were performed in the U.S. in 2010. About half of those involved silicone implants.