The American Dental Association (ADA) recommends: "Make sure to replace your toothbrush every three to four months, or sooner if the bristles are frayed. A worn toothbrush won’t do as good of a job cleaning your teeth."
Dr Joshua, Naperville dentist, agrees with the ADA position on when to change your toothbrush. She also suggests that you change your toothbrush after you have had a cold or the flu to prevent the transmission of germs. If you are using an electric toothbrush, the same rules apply. If the bristles are frayed and not straight, you should change your toothbrush head. You can also mark your calendar so on the January 1st, April 1st, July 1st and October 1st, change your toothbrush!