OBJECTIVETo investigate the changes of caries susceptibility factors during the transition from caries-free to caries in three-year-old children.

METHODSThe study included 144 caries-free children aged 34-38 months. All participants underwent clinical examination and full-mouth supragingival plaque collection.Survey of children's oral health behaviors involving feeding habits and oral health care was also taken from children's parents of all participants. The children were reexamined 6 and 12 months later. According to the potential changes of caries status in twelve months follow up, all the participants were divided into three groups: caries-free group (caries free children in twelve months follow up), caries at 6-month group (children who were found with caries or cavities fillings at six months review) and caries at 12-month group (children who were caries free at six months but found with caries or cavities fillings at twelve months). Streptococcus mutans (Sm)and Streptococcus sobrinus (Ss) loads were compared among the three groups by real time fluorescence quantitative polymerase chain reaction (FQ-PCR).

RESULTSOne hundred and thirty children completed twelve months review, the dropout rate was 9.7% (14/144). At the end of twelve months follow up, the number of children in caries-free group, caries at 6-month group and caries at 12-month group was 58, 44 and 28 respectively. The changes of oral behavioral habits in caries-free group, caries at 6-month group and caries at 12-month group during twelve months follow up were not significantly different (P > 0.05). At baseline, the frequency of sweets consumption and eating sweets before sleeping in caries-free group was significantly lower than that in caries at 6-month group and caries at 12-month group (P < 0.001). At baseline, the quantity of Sm and Ss in caries at 6-month group[copy number of Sm: (6.33 ± 2.21)×10(3), copy number of Ss: (1.99 ± 0.45)×10(3)] was significantly higher than that in the caries-free group[copy number of Sm: (5.81 ± 2.43)×10(3), copy number of Ss: (1.34 ± 0.53)×10(3)] (P < 0.05). There was no significant difference in the quantity of Sm and Ss in the caries-free group and caries at 12-month group(P > 0.05). At six months, the quantity of Sm and Ss in caries at 12-month group was significantly higher than that in the caries-free group although both groups of children were caries-free at six months (P < 0.05).

CONCLUSIONSThe quantity of Sm and Ss increased six months before the caries onset in three-year-old children.High frequency sweets consumption and eating sweets before sleeping were important susceptibility factors for caries onset in the future.