As soon as the bristles on your tooth brush are starting to bend, it is time to get a new one. A good rule is to change your toothbrush, or the head of an electric toothbrush, at least with each season, or every 3 months.  To prevent a build up of bacteria on your toothbrush store it upright so that it dries out between uses, don’t let it touch anyone else’s toothbrush and don’t sit it anywhere close to where it might get contaminated with splashes from the basin. Keep it sitting well away from the basin or toilet area. 

For optimal dental health, brush twice a day with a very soft tooth brush and a soft circular motion to prevent wear at the necks of the teeth, called tooth abrasion. The protective tooth enamel can literally disappear with over vigorous brushing, and the teeth can get sensitive and weaker. Damage to the gum at the edge of the teeth, called gum recession, can occur with over vigorous tooth brushing or with tooth brush bristles that are too hard, where the gum pulls back away from the vulnerable root surface of the tooth and makes the teeth look longer. 

There is no substitute for a good flossing routine once a day, preferably at night time, after brushing; if you're one of the many people who don't do it regularly, using an electric toothbrush can help gum tissue stay healthier, and a 

As for how to brush effectively, it's not a back and forth scrubbing motion, it's like a soft circular motion, for 2 minutes in the morning and last thing at night, with no snacking or drinks after, except for drinks of water. 

If you’ve been sick or travelling discard your toothbrush or toothbrush head, and get a new one.