Problem statement: The final product of amelogensis which generates in three subsequent phases is dental enamel. These Phases are divided into: excretory, calcification and maturation stage of enamel. While these specific complex events, are affected by specific agents, the act of amelogenic cells will be disturbed and hence the results of this process is improper and imperfect enamel production which vary in an spectrum from a little but discoloration to complete loss of enamel. Approach: The

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... im of this study was to determine the prevalence assessment of enamel defect in permanent first molar in 6-7 years student of Kerman city. Permanent first molar of students 844 boys and 793 girls was examined. Their demographic information and teeth information was collected in a questionnaire and questions to investigate etiology of hypoplasia in three stages were asked from the parents. Results: From 1637 students that enrolled in this study, 123 cases had enamel defect at least in one plan of one tooth. Conclusion: Prevalence of hypoplasia in two genders was approximately the same and there was no definitive statistical difference between them. Buccal place was the most affected plan and permanent first molar was the most affected tooth. Assessment of etiologies of hypoplasia, ten major factors was detected: 38.2, 26, 21.9, 13.8, 9.8 and 6.8% had history of cesarean section, childhood disease, hepatitis A infection in infantile period and administration of medicines by parent meanwhile pregnancy, maternal disease during pregnancy and immature birth, respectively.