ObjectivesThis study aimed to analyse the 2010–2018 cohort data of the National Health Insurance Service to examine the association between applying sealants in the first molars of children and their early dental impairment.MethodsBased on the two‐level mixed effect model (individual four teeth), the study participants were divided into two groups: those with sealants on all four first molars and those without sealants to determine the association between sealants and early impairment. We analysed teeth that had undergone extraction or canal filling to determine early impairment.ResultsThe rate of early impairment in the first molars was approximately 7.4 times lower in the sealant group (0.65%) than in the non‐sealant group (4.83%). Early impairment of first molars was higher in females, medically cared for and in rural populations. It was also higher in the maxillary first molars (3.7%) than in the mandibular first molars (3.49%), in more rural areas, and in lower household income groups. In generalised linear mixed models, first molars with sealants were 14.9% less likely to have early impairment than those without sealants (p = 0.000).ConclusionsThe study findings suggest that applying sealants on the first molars is important to prevent early dental caries development and prolong the functional integrity of first molars. In addition, we found that maxillary first molars were more susceptible to early impairment than mandibular first molars, even when sealant was applied.