You should change a manual toothbrush every 90 days, or after any illness. We all have bacteria in our mouths — and therefore, on our brushes — but even healthy bacteria starts to become aggressive after three months. In addition, if your brush begins to show signs of extreme wear before the 90-day mark, you should replace it: Damaged bristles lose their effectiveness and can injure gum tissue.
Electric toothbrush heads tend to last a bit longer because we don’t put as much pressure on them. However, be sure to replace them right away if they show any wear. After three months, it’s a good idea to soak the brush head in a sterilizing solution made of 1 teaspoon of bleach and 1 cup of water to remove any bacterial buildup. (This is also an excellent way to disinfect long-term equipment such as retainers, whitening trays and mouth guards.)