In modern orthodontics, the most emphasized problems are, as Bjork said in his literature, how to control entirely the growth and development and conservation of teeth: how to diminish the damages of orthodontic treament to the teeth. As a solution of these problems Bjork introduced the method of early orthodontic diagnosis. The study of occlusion of primary dentition has two main purposes: 1. To observe the change of occlusion as age increases. 2. To predict the change of occlusion to make early diagnosis possible. From early nineteeth century, Bogue (1908) started the study of occlusion of primary dentition, followed by Bonnar (1956-1960), Kisling (1973-1976), Ravn 1975), Foster (1969), Moyer (1969), etc. These studies have been used in the diagnosis of preventive orthodontics. In Korea, the study of occlusion of primary dentition was started in 1977. The second study was reported in 1978. Through the third report in 1979, author will introduce sagittal relation in the canine and incisor regions of Korean children.