The Silver IUD is exactly the same as the Copper one as regards the shape, size or amount of copper in the spiral.
In Silver IUD’s, the Copper wire contains a Silver core, making up approximately one third of the total diameter. This Silver core prevents the Copper wire breaking when corroded in the uterus. This is due to Silver is a noble metal and it is not corroded by the body acids contained in uterine fluids. The fact that the Copper spiral remains intact throughout the useful life of the IUD is an important added value and reinforces the safety of the contraceptive effect.