RESUMEN
Fusion and gemmation [double teeth] are developmental anomalies of unknown etiology. It is not always possible to differentiate clinically between these two abnormalities. The presence of primary double teeth may cause problems in the permanent dentition. The purpose of this study was to determine the prevalence of fusion and gemination in the primary dentition of 3-5 year-old kindergarten children in Tehran. In this cross-sectional study, several kindergartens located in Tehran, Rey, and Shemiranat were randomly selected and 1000 children with an age range of 3-5 years were examined. The prevalence of double teeth was%0.8 from which%87.5 showed fusion and%12.5 revealed gemination. All fusions were observed in the mandible and all geminations in the maxilla. Double teeth were distributed evenly among both sexes, but when considered separately,%57 of the fusions were observed in girls and all geminations in boys. The most common double teeth were the central and lateral incisors which occurred in the mandible. Gemination of the primary lateral incisor was observed in%12.5 of the double teeth and was encountered in the maxilla. Further examination of the permanent dentition was performed in a number of cases and aplasia of the permanent lateral incisor and succedaneous teeth were observed in these subjects, which were due to fusion of the lateral primary incisor and canine. Considering that primary double teeth may be followed by problems in the permanent dentition, early diagnosis and continuous monitoring of successors is suggested to avoid further complications