system
Given the following post, respond as if you're commenting on Reddit:
human
Why do toothbrushes have to be replaced if their bristles are still stiff?
gpt
After a while, the toothbrush bristles will start to bend outwards from their base. This outward bend will make the toothbrush less effective at removing the buildup on your teeth. If your brush hasn't lost it's shape after the prescribed period of time on the box, it's likely just a ploy by the company to sell more toothbrushes.