Keeping teeth clean is a priority when it comes to health and hygiene because it removes bacteria and plaque from the mouth, both of which can harm the teeth. Having clean teeth starts with proper toothbrush care. The American Dental Association guidelines state that a toothbrush should be changed every few months or as soon as the bristles start to show signs of wear.
Since the human mouth carries many different organisms that can cause infection, these organisms can be easily transferred to a toothbrush where they can potentially grow and from which they can re-enter the mouth during brushing.
If there are breaks in the skin or mucous membranes in the mouth, those harmful bacteria can enter the body, but if so, they’re generally taken care of by body processes. However, keeping a toothbrush clean and regularly changing it is an important part of maintaining a healthy mouth.