The white spots are minor hypo-calcification spots. During the teeth whitening process, the chemical reaction of the peroxide breaking down generates some slight heat inside the tooth, and this heat causes the pulp and dentin to expand. This expansion pushes water out of the tooth. This is what we refer to as dehydration of the teeth. Some of the whitening that you see is most likely initial dehydration, not actual whitening. This usually lasts around 72 hours.