Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 19 0 2022 06 28 3869 3869 Razieh Khanmohammadi Department of Pediatric Dentistry, School of Dentistry, Tehran University of Medical Science, Tehran, Iran Bahman Seraj Dental Research Center, Department of Pediatric Dentistry, School of Dentistry,Tehran University of Medical Science, Tehran, Iran AND Department of Pediatric Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran Ahmadreza Salari Private Practice, Tehran, Iran Firoozeh Alipour Department of Pediatric Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran 2020 11 28 2022 06 01 Molar-incisor hypomineralization (MIH) lesions are common inchildren. The prevalence of MIH is variable in different communities. However, information regarding the prevalence of MIH in the Iranian population is limited. This study sought to assess the prevalence and etiological factors of MIH in 7-12- year-old children in Tehran. Materials and Methods: This descriptive, cross-sectional study evaluated 1028 elementary students between 7-12 years, selected from different districts of Tehran in 2017. The frequency of MIH in the maxillary and mandibular molars and incisors was determined by clinical examination. In order to assess the role of different factors in the development of MIH, a questionnaire was filled out by the mothers regarding problems during their pregnancy, medical history of children, and age of occurrence of systemic conditions (if any). The effect of different factors on the development of MIH was analyzed by the logistic regression test. Results: The prevalence of MIH was found to be 25.6%. The delivery condition of the  mother (P<0.001), history of urinary tract infection (P<0.011), history of chickenpox (P<0.018), and frequent use of amoxicillin during childhood (P<0.041) significantly affected the occurrence of MIH. The most commonly involved teeth were the mandibular left first molars.  Conclusion: The prevalence of MIH in our study population was within the range reported in the literature. Considering the relatively high prevalence of MIH in 7-12-year-old children, pediatric dentists should pay special attention to treatment of MIH. https://fid.tums.ac.ir/index.php/fid/article/view/3869