The target population of the sealant program was first grade primary school children who had fully erupted and caries-free first permanent molar teeth. Multi-stage random sampling was employed. Six out of 12 CUPs were randomly selected and then one or two schools from 12-40 schools in each CUP were used. Finally, there were 11 schools. All eligible children with parental or guardian consent were included. For all children, the selected teeth were sealed by six dental nurses who had attended a refresher course at the Faculty of Dentistry, Prince of Songkla University For sample size calculation, the following where, n was a formula was used's; n minimum sample size, p was proportion of children with full sealant retention, q was (1- p) or the proportion of children with loss of sealant retention teeth (both partial and total loss), and half size of the 95% confidence interval. The estimate p, obtained from a pilot survey, was 0.65, d 0.065 and Z at 95% confidence 1.96. Therefore, the minimum sample size was 208. The acquired sample size in this study was 206 children with 347 teeth.