For removable retainers: brush gently with a soft-bristled toothbrush and cool water after each use, and soak at least once a week in a retainer-cleaning solution to prevent build-up. Avoid hot water — it warps the plastic. When you are not wearing it, store it in its protective case. For fixed retainers: brush carefully around the wire and use floss threaders or an interdental brush to clean underneath it daily.
Yes, but this is worth discussing with your orthodontist before continuing with a standard retainer. Many patients who grind at night are better served by a dual-purpose hard-acrylic retainer that maintains tooth position and protects against grinding at the same time. Wearing a thin removable retainer over a grinding habit can cause it to wear through or crack faster than expected. Speak to your orthodontist, who can advise on the right retainer type for your situation.