Dentists usually say that they will last 6 months, however, I would not wait longer than a month before going through with the actual filling (or whatever needs to be done next). It's very uncommon that the temporary filling will last all 6 months. After a month of having it, it could get terribly bad within a couple of days. The only thing is, you don't know what will happen to your tooth after a month. You could get serious tooth pains or no tooth pains at all. The worst possible thing that could happen is that the tooth will decay (if you wait longer than 6 months). I would recommend going through the next step after a month. Ultimately, I wouldn't wait any longer than 45 days.
