Purpose: The aim of this study is to investigate the effects of two different types of fissure sealants on LF measurements. 

  Materials and Method: In this in vitro study, 86 extracted permanent third molars were divided randomly into two groups and clear or opaque sealant was applied on the occlusal surfaces. Two examiners performed pre- and post-seal fluorescence measurements twice with one week interval by employing DIAGNOdent device. Finally, measured values were evaluated through the statistical paired t-test by means of SPSS 17 software.

  Results: The mean value of LF measurements increased significantly due to the application of clear sealant (p= 0.001) while the statistical changes in this measurement was negligible after applying opaque sealant (p= 0.311). 

  Conclusion: Clear sealants increase the LF measured values but opaque sealants cause almost no changes. Therefore DIAGNOdent device is not reliable for detecting caries beneath the clear sealant.