Iranian Dental Association Journal of Iranian Dental Association 3060-8201 17 2 2005 05 01 Prevalence of posterior crossbite in (3-5) years – old nursery schools' children in Zahedan in 2002 - 2003 100 104 EN Homa Noorollahian Saeed Bordbar Journal Article 2007 05 14 2013 02 25 Prevalence of posterior crossbite in (3-5) years – old nursery schools' children in Zahedan in 2002 - 2003 Dr. H. Noorollahian * - Dr. S. Bordbar** *- Assistant Professor of Pedodontics Dept. - Faculty of Dentistry –Zahedan University of Medical Sciences. **- Dentist. Background and Aim: Posterior crossbite is a common phenomenon in primary dentition which is classified in three general types of skeletal, dental and functional which are not mostly self – corrected, however a suitable and on – time treatment may prevent it to change into a skeletal disorder. The goal of this study was to determine the prevalence of posterior crossbite among 3-5 year-old nursery school's children in Zahedan. Materials and Methods: In this cross – sectional descriptive study, data were gathered through clinical examination and questionnaire in 870 children, 500 boys and 370 girls. The unilateral crossbite was characterized by cusp – to – cusp position of molars in central occlusion and the mandible, to find a stable occlusion, had to slide to one side. If there was no midline deviation it was classified as bilateral cross-bite. The data were analyzed using descriptive statistical methods and X2 test. Results: The prevalence of posterior crossbite in the studied group was 3.2%. The posterior cross-bite was more in girls (4.3%) than boys (2.4%). Unilateral posterior crossbite was observed in 92.8% of cases and bilateral posterior crossbite was seen in 7.2%. Conclusion: The prevalence of posterior crossbite was 3.2% in (3-5) year – old children in Zahedan nursery schools. Key words: Posterior cross bite – Primary dentition - Prevalence.