You need to keep your toothbrush too clean, which everyone does by washing the brush with plain water before and after brushing. There are certain plastic covers available now days Which act as a protective cover for the bristles avoiding them to get contaminated. Make sure you change your brush on regular intervals. Usually when you observe that your bristles have started bending, it's an indication to change it. It usually lasts for 2-3 months max. Avoiding doing this may make the bristles more sharp and result in abrasion of the teeth.