What should I do during my fast, while wearing a dental retainer, regarding the following points: placing the retainer in a cup of water when I take it off, how to deal with rinsing my mouth while the retainer is in, and what about the white secretions that accumulate around the mouth due to the retainer during sleep?

Using the device does not cause harm if it is dry and no water has been swallowed. It is sufficient to spit out the water after rinsing the mouth until it is highly probable that it has been expelled. Swallowing residual wetness does not cause harm unless one is certain of having swallowed gargling water. Secretions that form around the device upon waking must be removed, but anything that enters the body cavity from them during sleep does not cause harm.