Temporary dental crowns are the crowns that you wear while the dental laboratory is making your final, perfect dental crown. These are necessary only as a hold over, so that you are not toothless in the interim period between the time you lost a tooth or part of it, and the time you get your dental crown. This is usually about a week, but certain circumstances (holidays, illness, scheduling, locational problems, problems with the final crown that require more time to fix etc.) may extend this period of time. Temporary dental crowns fall off because they are not meant to last for a long period of time, but only a short one, and when they do, the best thing to do is to call the dentist to get another one.