What is the ruling on using teeth whitening trays during the day in Ramadan?

Teeth whitening trays do not invalidate the fast if they are tightly sealed and nothing leaks into the mouth, or if whatever comes out of them is spit out. However, if the materials leak and are swallowed by the fasting person, then it is not permissible to use them, as they may lead to the invalidation of the fast. This is analogous to the Prophet (peace and blessings of Allah be upon him) forbidding exaggeration in sniffing water for the fasting person, for fear of water leaking into the stomach. But if the materials are not strong and can be guarded against, there is no harm in using them.