With such a short history of research in this area, long-term studies are still needed.
Doctors have not yet done long-term studies to know how well this works over time.
One long-term study found that, after 10 years, 20 out of 100 leads had problems.
She also said better procedures were needed for long-term studies.
But there were two more important findings in this long-term study.
Yet there have not been long-term studies to prove safety.
Some critics say the lack of long-term, independent studies is significant.
Long-term studies on its safety and effectiveness are still under way.
There have been no long-term studies, but consequences are already showing up.
To date, there have been several large, long-term scientific studies.
