Is this type of magnet safe to use uncovered with fabric, or will it damage my doll?

Ive never seen anyone use these types of magnets before, and im worried it will damage my reborns or stain their mouths somehow. Should i not use it? i bought them at the dollar tree :)

I do not want to add fabric to the magnet because the magnet is not very strong when i tried to cover it and did not attach to my reborns mouth.