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

https://martinjzxj106.tearosediner.net/the-length-of-time-does-teeth-whitening-last-a-realistic-timeline

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