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

https://blogfreely.net/dernesvhbz/foods-that-spot-your-teeth-and-how-to-fight-them

Fluoride varnish or remineralizing pastes can be applied after whitening to reinforce enamel and minimize level of sensitivity while preserving your brighter smile.