From the point of view of the law of human growth and development, different stages have their own development rules and characteristics, and there are also different development stages of dental development. If we take targeted health care measures according to the characteristics of different stages, we can achieve twice the effect with half the effort. Before the teeth erupt, the embryos of the milk teeth and permanent teeth develop and grow in the jawbone. The development and calcification of the baby teeth occurs mainly during the embryonic period and is directly influenced by maternal health, nutrition, disease and genetics. The development and calcification of permanent teeth, on the other hand, occurs mainly during infancy. During this period HO, the external environment, especially mineral salts in the diet, vitamins, and trace elements in drinking water such as fluoride, are closely related to tooth development. It is a complex and long process from the eruption of the first milk teeth in the mouth to the eruption of the permanent teeth and the completion of the establishment of the occlusal relationship. According to the growth and development of children, tooth eruption and replacement, the dental development of children and adolescents can be clinically divided into three dental stages: The milk teeth: from the beginning of the eruption of milk teeth to the first permanent tooth eruption is called the milk teeth period. Milk teeth are the chewing organs of young children, and the functional stimulation of chewing can promote the development of jawbone and dental arch. Maintaining the normal development of the jawbone and dental arch is a condition for the permanent teeth to be properly aligned. Adequate chewing not only chews solid food, but also reflexively stimulates increased saliva secretion, which helps digestion and absorption of food. Therefore, maintaining the health and integrity of the milk teeth is an important task at this stage. This stage is the period when the caries of milk teeth (tooth decay, insect tooth) starts to develop and gradually increases. Early detection and treatment are the important measures to avoid caries secondary to endodontic or apical disease. It is very important to preserve the milk molars clinically as much as possible. Premature loss of milk molar will cause malocclusion. It is very necessary to strengthen oral hygiene education and make parents understand the importance of preserving milk teeth. Mixed dentition: From around 6 weeks of age, permanent teeth begin to erupt and the milk teeth are replaced in turn, usually around 12 years of age, the milk teeth are replaced. This is the main developmental period of the jawbone and dental arch of children, and it is also a critical period for establishing the occlusal relationship of permanent teeth. It is one of the important tasks in this period to prevent malocclusion, correct it early, and induce the establishment of normal dentition. This period is also the stage when the caries of permanent teeth starts to develop, and most of the caries of milk teeth have been seriously destroyed in this period. Endodontic treatment, such as root canal treatment, is also relatively more frequent in this period, which needs to be combined with the necessary treatment at the age. Young permanent teeth: At about 12 years old, all the milk teeth are replaced, and at about 15 years old, all the permanent teeth have erupted except the third molar, and there are no milk teeth in the mouth at that time. The so-called young permanent teeth refer to the permanent teeth that have erupted but the roots are not yet fully formed. In this period, some of the permanent teeth have basically formed their roots, but the pulp cavity and root canal are still relatively thick; some of the permanent teeth have just started to erupt and their roots have not yet been fully formed. The first permanent molar is the earliest among the permanent teeth, at the same time, due to its anatomical characteristics, such as the deeper sulcus on the surface of the teeth, the incidence of caries is higher and the caries damage is also more serious. Although the second permanent molar erupts around 12 years old, the incidence of sulcus caries is also high, therefore, preserving the first and second permanent molars as much as possible is the main task in this period. After the first and second permanent molars are fully erupted, the early sulcus closure is the measure to effectively prevent the caries of permanent molars.