Invention on Demand

摘要

Consider the humble toothbrush. Its engineering "has,really changed in the last 50 years. There used to be one simple type—a rigid handle with bristles exactly the same length and stiffness. It was easy to make. Then along came brushes with different handle lengths to suit adults and children. Then dentists realized that soft bristles are better for the gums. People have different-size mouths that can make it difficult to reach all the way back to the molars without discomfort, so along came flexible joints in the handles. Those soft bristles were still great for the gums, but harder bristles could help dislodge stubborn food particles from teeth, so toothbrushes were designed that had soft bristles on the outside and stiffer bristles inside. There was a limit to how many times you would move the brush up and down before you just got tired of brushing, so an electric motor was added that increased the number of strokes without any additional effort. Many people took toothbrushes on trips and forgot toothpaste, so a toothbrush with the toothpaste stored in the handle came along. Today, we have sonic toothbrushes whose frequency is much higher than any motor's.