To compare the effect of different etching modes on the bond strength and durability of a new type of pit and fissure sealant on the surface of human enamel in vitro after storage in water (37 ℃) for 24 h and thermocycling for 5000 times.

In the present study, a total of 30 caries-free human third molars were selected and the enamel plane was exposed, of which 24 specimens were used for this experiment. The specimens were divided into two groups according to random number table method (n = 12) , and further divided into 3 subgroups (n = 4) according to different etching modes: phosphoric acid group (group A) , universal adhesive group (group B) and phosphoric acid + universal adhesive group (group C) . After specimen preparation, the shear bond strength (SBS) test was carried out after 37 ℃ water storage for 24 h and after thermocycling for 5000 times, respectively. The data from SBS were analyzed by using Three-Way ANOVA (storage condition, etching mode and color of pit and fissure sealant) , and Turkey/Games-Howell (α = 0.05) . The fracture mode was analyzed by light microscope and fracture surface on enamel was observed by scanning electron microscope (SEM) with the application of energy spectroscopy.

After storage in 37 ℃ water for 24 h, the SBS of group C was (22.18 ± 4.55) MPa, which was significantly higher than that of group A (16.07 ± 4.17) MPa (F = 11.779, P = 0.002) and group B (16.40 ± 3.01) MPa (F = 13.436, P = 0.001) . No significant difference was detected between group A and group B (F = 0.068, P = 0.797) . After thermocycling for 5000 times, the SBS of group A was (12.69 ± 3.00) MPa, that of group B was (0.00 ± 0.00) MPa, and group C was (12.17 ± 2.85) MPa, all of which decreased. There was no statistical difference in the change of SBS in group A (F = 1.504, P = 0.225) , whereas significant decrease was found in group B and C (F_{B group} = 165.896, P_{B group}<0.001; F_{C group} = 51.665, P_{C group}<0.001) . No statistical difference was found between group A and group C (F = 0.182, P = 0.674) , both of which were significantly higher than that of group B (F_{A group} = 213.353, P_{A group}<0.001; F_{C group} = 219.470, P_{C group}<0.001) . Three-Way ANOVA analysis of variance revealed that the interaction within these three factors was not statistically significant (F = 1.376, P = 0.254) . After thermocycling for 5000 times, the type Ⅱ fracture mode was significantly increased, but no enamel prisms fracture was detected in group B. The downtrend of enamel prisms fracture in group C was greater than that in group A.

The bond strength of pit and fissure sealant on enamel could be significantly enhanced by the combination of phosphoric acid etching and universal adhesive after storage in 37 ℃ water for 24 h. The durability of pit and fissure sealant after acid etching of dental enamel was improved.