OBJECTIVETo compare the changes of enamel surface and cross-sectional microhardness of artificial caries immediately and after the twice demineralization through coating resin infiltration, fluoride varnish and fissure sealant.

METHODSA total of forty bovine lower incisors enamel samples with artificial caries lesions by the demineralization liquid were used in the experiment. The specimens were then randomly divided into four groups as group A(resin infiltration), B(fluoride varnish), C (fissure sealant), D(control), 10 specimens in each group. The samples were sectioned vertically into two halves through the centre. One half of each sample the surface and cross-sectional microhardness was measured. The other half was put into demineralization liquid for 14 days, then the surface and cross-sectional microhardness was measured again. The cross section morphology of the samples was observed by scanning electron microscope.

RESULTSThe surface of enamel had the highest microhardness value, and with the increase of cross- sectional depth, the microhardness value declined gradually. Variance analysis showed that the difference was statistically significant in the cross-section of different depth among the four groups(P<0.05). The microhardness values of the surface and the cross- section at 40 µm of each group in immediate measure showed the values were significantly higher in group A, B and C than in group D. There was no significant difference in the microhardness value of cross-section at 80 µm between group A[(324 ± 17) kg/mm(2)] and group C[(316 ± 20) kg/mm(2)], but they were significantly higher than group D. There was no significant difference between group B[(303 ± 13) kg/mm(2)] and group D[(294 ± 23) kg/mm(2)]. At 120 µm level, the microhardness value of group A was significantly higher than those of the other three groups. After the twice demineralization, the enamel surface microhardness value of the specimens was the same as the first measurement. In the cross-section at 40 µm level, the microhardness value was equal to the value of cross-section at 80 µm level of the first measurement. In the cross- section at 80 µm and 120 µm level, the microhardness value of group A was significantly higher than those of the other three groups.

CONCLUSIONSResin infiltration can effectively strengthen microhardness of enamel surface and cross-section of different depth of artificial caries.