Fluoride varnish or remineralizing pastes can be used after whitening to reinforce enamel

https://kylerbqsz130.bearsfanteamshop.com/foods-that-stain-your-teeth-and-how-to-battle-them

Fluoride varnish or remineralizing pastes can be applied after whitening to strengthen enamel and lessen sensitivity while preserving your brighter smile.