MOST people tend not to brush their teeth when they are sick. But that is precisely when you should. You are probably taking a lot of medication, some of which is sugar-coated; this is especially true of medication for kids. This could then lead to caries for those on long-term medication.
If you have to stay in hospital for treatment, make sure to bring along toothbrush and toothpaste to keep your teeth and gums in the best possible condition.
