A toothbrush is the main instrument for oral hygiene, that is the reason why you must choose the most appropriate brush according to your age and your mouth characteristics (adult or child).
Brush filaments are the most important thing to take into account. These filaments should be either soft or medium strength so as to clean your teeth deeply, not damaging the dental enamel and providing a soft massage to the gums.
Sometimes, a stronger brush is needed to remove stains, such as tobacco or coffee, from the enamel.
Brush filaments must have the best quality with round endings in order to reach the smallest cavities in between teeth.
You must change your brush when the filaments are either bent or worn out. If a toothbrush is in a bad condition, it can damage your gums and it is completely useless for oral hygiene.