A ramdomised controlled trial and cost-utility analysis of pit and fissure sealant programme in first molar in 7-8 years old children in Guangzhou

INTERVENTION: Group A:sealing the first constant molar occlusal surface with ICDAS scores of 0‐2;Group B:sealing the first constant molar occlusal surface with ICDAS scores of 0‐3; CONDITION: Dental caries PRIMARY OUTCOME: ICDAS; SECONDARY OUTCOME: sealant retention;Visible plaque index;Demographic information;Oral health behavior information;Cost; INCLUSION CRITERIA: 1. Sign and date informed consent; 2. Second grade primary school students, male or female; 3. Good general health state; 4. Deep pits and fissures and are completely exposed to the mouth; 5. Be able to participate in clinical research for a period of 24 months; 6. At least 2 maxillary or mandibular first molars have completely erected and reach the occlusal plane; 7. At least having one tooth with an ICDAS score of 3, another with a score of 0‐2; 8. Ability and willingness to follow the research procedures required by the research protocol.