We do not recommend using dental floss to hang crystal chandelier parts. We've had reports of people using dental floss in windows to make sun catchers.
Dental floss is easy to come by so it's only natural people think of it. There are many types of dental floss including waxed and unwaxed in mono-filament (single) and multi-filament (multiple) thread styles. The standard multi-filament can have as many as 1000 strands which twists six times per inch to add strength.
Using standard tensile strength testing shows that the longer the length of dental floss the weaker the floss. A 20-inch piece is more than 3.2 times weaker than a 10-inch piece. A 30-inch piece is again half as weak as the 20-inch. Over time a sun-drenched window would further dry out and weaken the dental floss.
The "tensile strength" is the amount of pressure needed to burst the cord or floss. It's a common unit of measure for cord.
A 15# test fishing line is 57 times stronger than dental floss. The heavier the prism the stronger the cord or line you'll need to hang it. Don't run the risk of damage to your beautiful prisms. Test the line and calculate what the burst or tensile strength is.