Background: Preterm labor is defined as labor before 37 weeks of gestation, which is associated with neonatal mortality. Due to contradictory results of studies conducted on the relationship between preterm labor and dental decays and lack of research in this regard in Iran, the present study was conducted with the aim of evaluating the relationship between DMFT (decayed, missing, and filled teeth) index and preterm labor in pregnant women in Hamadan. Methods: This study is a case-control study. The total number of samples was 227 pregnant women studied in two groups, 114 women in case and 113 women in the control group. The data collection method was interview and examination and the data collection tool was a questionnaire consisting of three sections, including demographic, midwifery, and dental information. The data were analyzed through SPSS software version 16.0 using descriptive and analytical statistics, independent t test and chi-square and at the significance level of P<0.05. Results: The mean age of the subjects was 28.41±6.26 years. The mean score of the DMFT index was 13.02±6.20 in the case group and 10.70±6.12 in the control group, indicating a statistically significant difference between the two groups (P=0.005). The results showed that there was no significant relationship between DMFT index and preterm labor (P=0.779). Conclusions: Based on the results of the study, the DMFT index is high in women with preterm labor, so providing necessary education before and during pregnancy by health service providers and mass media for pregnant women is essential to maintain and promote oral hygiene and reduce the complications of pregnancy