The progression rate of newly occurred pit and fissure incipient caries of first molars was investigated every 6 months for 24 months. The subjects were 93 1st and 2nd grade elementary school children who did not perform school-based fluoride mouthrinsing. The progression rate after 12 months was approximately 60%, and the non-progression rate was approximately 40%. Cumulative progression rates after 12 months were approximately 60% for the 1st grade, and 40% for the 2nd grade, and the same rates after 24 months were 70% for the 1st grade, and 60% for the 2nd grade. These data were compared with our previous data derived from the same grade of elementary school children who performed school-based fluoride mouthrinsing. There was no statistical difference in the progression of incipient caries between these two schools. This lack of difference may be explained in terms of the complicated form of pits and fissures, or it may be that the fluoride mouthrinsing period was too short to be effective against caries progression.
