This is because, after drinking acidic beverages or vomiting, the contact between the acid and the teeth will soften the enamel and you will have to wait for the enamel to be hardened again by saliva. If you brush your teeth instantly after having an acidic drink or vomiting, the speed by which your tooth enamel is wrecked will go up. Avoid brushing your teeth for at least an hour after having such acidic beverages as orange juice. Research has shown that it takes an hour for saliva to disclose its neutralizing effects after drinking an acidic beverage.