Faulty breast implants made by PIP, the French company that sparked a global health scare, do not pose any long-term medical threats, British health authorities said in a final report Monday.
The silicone gel filler used inside the implants is not toxic and does not increase the risk of breast cancer, the National Health Service's (NHS) Medical Directors group said.
But the experts warned that the implants, which used industrial-grade silicone gel intended for use in mattresses, are twice as likely to rupture as other brands.
More than 400,000 women worldwide are believed to have received implants made by PIP -- which was shut down in 2010 -- and many countries have urged women to have them removed.
"This has been an incredibly worrying time for women," said the NHS group's leader Professor Bruce Keogh.
"We have been determined to look thoroughly at all available evidence so we are able to give them the best clinical advice possible."
Keogh said repeated tests on different batches of PIP implants had been carried out in Britain, France and Australia and shown that the implants were not toxic.
"We do not believe they are a threat to the long-term health of women who have PIP implants," said Keogh.
"We have, however, found that these implants are substandard when compared to other implants, and that they are more likely to rupture."
The report said PIP implants have a 15 percent to 30 percent chance of rupturing after ten years, compared to 10 percent to 14 percent for other brands.
Rupturing of the PIP implants has caused symptoms such as tenderness or swollen lymph glands in a small proportion of women but there is no link to cancer despite earlier fears, the study said.
PIP's founder Jean-Claude Mas, 73, was charged in January with causing "involuntary injuries" in the case and in March was jailed in the southern city of Marseille after failing to pay his 100,000 euro ($125,000) bail.
The NHS study looked at data on 240,000 implants of differing brands, given to 130,000 women in England.