The purposes of this study were to determine the prevalence rates of maloctlusion, . to scrutinize sex differences in these rates and to estimate the need of orthodontic treatment in a group of Thai children A total of 873 Th~i children, 458 boys and 415 girls, were randomly selected from schoolchildren in 4 districts of Chonburi province. All of them, aged 12-14 years, had permanent dentitions and had received no orthodontic treatment. The status of a child's malocclusion was scrutinized from the study model. By using the basic method for the recording of malocclusion proposed by the World Health Organization, we concluded that :1. among the dental anomalies, missing permanent teeth was the most common malocclusion (31.80%). In regard to space ano~alies, crowding was the ~ost common malocclusion (37.50%). In regard to occlusal anomalies, midline shift was the most common Ralocclusion (19.06%); 2. there was significant sex difference in the prevalence rate of excessive overbite which was more common in the boys; 3. no orthodontic treatment was required in 17.877. of the children while 16.387. were considered necessary to follow the occlusal change, 45.707. were in need of orthodontic treatment and 20.057. were in immediate need of orthodontic treatment, respectively.
