Objective   To explore the influence of pit and fissure sealant and other relevant factors on caries rate of first permanent molars among primary school students in Liaoning province.

  Methods  The participants of the two-stage survey were 7 770 students aged 7 – 12 years recruited with multi-stage stratified random sampling from 32 rural/urban primary schools in 8 municipalities of Liaoning province. In the first oral health examination conducted by dentists during 2019 among all the participants, 2 393 were identified as having indications of fissure sealant; of them, 1 254 receiving fissure sealant were assigned into a observation group and 1 139 not having fissure sealant were regarded as controls. Then the second oral health examination and a self-administered or parents-involved questionnaire survey were carried out among the 2 393 students during 2020 to explore the prevalence and influencing factors of first permanent molars carries among the students of observation and control groups. Univariate and multivariate logistic regression analysis were adopted in data analysis.

  Results  The overall prevalence rate of first permanent molar caries was 24.45% for the 2 393 students and the prevalence rate was significantly lower in the students of the observation group than that in the controls (22.57% vs. 26.51%, χ² = 5.034; P = 0.025). The estimated protection rate of fissure sealant against first permanent molar caries was 14.86%. The results of multivariate logistic regression analysis revealed that gender, pit and fissure sealant, attitude towards regular dental clinic visit, and parental guidance on teeth-brushing were significant influencing factors of first permanent molar caries (all P < 0.05); among those influencing factors, female gender, negative attitude towards regular dental clinic visit, and without daily parental guidance on teeth-brushing were risk factors of first permanent molar caries (P < 0.05 for all) but having pit and fissure sealant was a protective factor against the caries (P < 0.05).

  Conclusion  Pit and fissure sealant has a protective effect on the occurrence of first permanent molar caries among 7 – 12 years old primary school students and the treatment needs to be promoted to reduce morbidity of first permanent molar caries among the students.