One hundred and forty-three patients ranging in age from 5 to 8 years participated in a pit and fissure sealant study using a half-mouth design. At the end of 18 months, for all permanent first molars, there was a 75.9% effectiveness with a net gain of 82, which was statistically significant. The sealant was present on the surfaces to which it was applied in 74% of the teeth. Application time was 8 minutes per quadrant and 5.5 minutes per tooth. The effect of treatment was similar to that reported for an unfilled BIS-GMA sealant in patients with similar teeth and similar ages. Loss of sealant from the permanent maxillary first molars did not appear to contribute to the initiation of dental caries. However, in 6 of 38 mandibular tooth surfaces, sealant loss may have been a factor.