The high risk children (having a previous caries experience at 5 years of age) from 2009, 2010 and 2011 birth cohorts (6-, 7- and 8-year-olds) from three counties (Østfold, Oppland and Hedmark) are selected. Children with at least two erupted first permanent molars in the same jaw randomly receive resin-based sealant or a fluoride varnish (Duraphat) during a routine dental examination. Children who already developed caries, had restorations or fissure sealants placed in first molars were excluded from the present study.