Navid Hosseini - Assistant professor, Department of Orthodontics, Yazd University of Medical Sciences
H. Azadikhah - Under graduate student , School of Dentistry, Yazd University of Medical Sciences
Soghra Yassaie - Associate professor, Department of Orthodontics, Yazd University of Medical Sciences
M. Tayyebi - Associate professor, Department of Orthodontics, Yazd University of Medical Sciences

Background and aim: cross bite is an Abnormal relationship between one or more teeth and their corresponding antagonist tooth so that the buccolingual or labiolingual relationship is opposite. Given the high prevalence and impact of these disorders, diagnosis and early treatment of this problem is very important. The aim of this study is to determine the prevalence of anterior and posterior cross bite for girls and boys who were ۷-۱۰ years old in Yazd, Iran.Materials and methods: This cross-sectional study on ۴۰۰ students aged ۷-۱۰ was carried out using clinical examination. Examinations were performed by the dentist and the presence or absence of crossbite and occlusal relationship was evaluated in the mixed dentition.Results: The prevalence of anterior cross bite is ۱۱% ,۱۲.۹% of girls and ۹% of boys and prevalence of posterior cross bite was ۳.۵%, ۴.۵% in girls and ۲.۵% in boys. prevalence of anterior cross-bite at age ۹ was ۱۱.۹% and posterior cross bite at age ۱۰ was ۷.۱% which are the highest rates reported .In mouth breathing children ۳۵.۷% and ۲۱.۴%, had anterior and posterior cross bite respectively. The anterior and posterior cross bite was more in Class II malocclusion than any other malocclusion. Among the cases investigated, mouth breathing and malocclusion have correlation with crossbites.Conclusion: Given the prevalence of anterior and posterior cross bite, mothers should be awared on the prevention and control of these disorders and also periodic examinations of children To prevent complications in future.

crossbite, Malocclusion, Child