Other surgeons said that doctors should follow the directions because much remains unknown about the durability and rate of rupture of silicone implants, which were the subject of intense and controversial class action suits in the 1990s. “If people blow these tests off, it will be detrimental from a scientific standpoint,” said Dr. V. Leroy Young, a plastic surgeon in St. Louis. “Patients will be walking around with failed implants and not know about it.” He said ignoring the directions could increase patient risk and that he would insist his patients have the tests. The F.D.A., criticized by some health advocates for allowing the silicone implants back onto the market, said it would monitor whether its recommendations were being followed. “We are certainly going to be looking into the compliance with the M.R.I.’s by doctors and patients,” said Donna-Bea Tillman, director of the F.D.A.’s office of device evaluation.