In the course of their work, dentists are often asked questions such as “How come this tooth has only been in place for a short period of time and is already so big?” Or, “How come this tooth is black when it first comes out?” or “Are children’s teeth softer than adults’?” And so on. This shows that parents also observe one important characteristic of decay of milk teeth: milk teeth are easily decayed and the decay progresses very fast. In fact, once the decay of milk teeth starts, it takes only three months to develop from a small black spot to a big hole. Many parents think that it is caused by children’s love of sugar, so what is the real reason why the decay of milk teeth is easy to happen and the decay of milk teeth develops so fast? In fact, milk teeth are more fragile than permanent teeth! The most surface layer of teeth is called enamel, which is the hardest part of teeth, like the armor of teeth, resisting various external stimuli. The enamel of baby teeth is thinner and less mineralized than that of permanent teeth, which means that the protective shell of baby teeth is not thick enough and hard enough, so it is no wonder that they are more prone to break down. In addition, the shape of the baby teeth is also more likely to retain food debris! There are many deep gaps on the biting surface of baby teeth, and there will be gaps between the teeth as the jaw bone grows, so the food is especially easy to remain, and it is not easy to brush it clean if you are not careful, and it becomes a breeding ground for bacteria, and it is not easy to brush it clean once the decay occurs and the surface of teeth becomes rough. In addition, children’s diet is mostly sticky, soft food with high sugar content, easy to ferment and produce acid, besides sugar, all kinds of cakes, bread, cookies, etc. are also foods that can easily cause tooth decay. Compared with eating a lot of sweets at one time, children prefer to eat a little bit later and a little bit later, which inadvertently prolongs the time for oral bacteria to produce acid and destroy teeth. Finally, children sleep for a long time, the mouth is in a static state, saliva secretion is less, which is conducive to bacterial reproduction saliva has the role of promoting enamel mineralization, that is to say, it can make the armor of teeth more hard, resist external corrosion, and has the role of cleaning the surface of teeth. However, when we sleep, the secretion of saliva will be significantly reduced, and at the same time, the bacteria multiply and produce acid, and the decay will happen unconsciously.