Background and Aims: This study aimed to assess the severity of tooth decay and related factors in children 5-7 years old, in 2016, in Tehran.

Materials and Methods: A descriptive and cross-sectional study was performed on 572 children aged 5-7 years old (300 girls and 272 boys) in public schools in Tehran, Iran. Severity of dental caries (number of decayed, missing, filled surfaces) recorded for C, D and E teeth according to WHO criteria. Data analysis was performed by Backward Linear Regression Analyses using SPSS 20 (P≤0.05).

Results: Assessment of dental caries severity according to the number of decayed surfaces showed generally higher figures in upper jaw. The order of average severity of carious teeth was C, E and D from low to high in both jaws. According to the results of Linear Regression Analysis, severity of dental caries was more than other children in boys (OR=1.83, 95%CI: 0.81-2.8), those visited dentist due to dental problems associated with pain (OR=1.17, 95%CI: 0.73-1.6), and those without fluoride therapy (OR=1.64, 95%CI: 0.58-2.6) in C, D and E teeth.

Conclusion: Flow the results, it was concluded that gender, level of mother's education, type of snack consumption, start age of tooth brushing, reason for dental visit and fluoride therapy affected severity of tooth decay.