Teeth decay is caused by acids excreted by certain types of bacteria that live in our mouth. Brushing your teeth using toothpaste kills them and stops buildup of acids, thus preventing teeth decay. But then, bacteria are living organisms and living organisms don't arise spontaneously. How do they keep occurring in our mouth even after getting rid of them all by brushing your teeth? One way I can imagine is through transferring of those bacteria through kissing. It's also possible that some of those bacteria were in the food, or some bacteria survived from your tooth brushing. I tried googling it, but I couldn't find the answer. But what are other possibilities? If we could somehow prevent continuous occurence of these kinds of bacteria in our mouth, wouldn't it be possible to prevent teeth decay without brushing your teeth?