Abstract:

Objective To evaluate the effects of dentine surface wetting and acid etching on the bonding strength of two kinds of Universal adhesives(Single Bond Universal(SBU) and Prime Bond Universal(PBU)). Methods Sixty human fresh caries-free molars were randomly divided into 6 groups to prepare a rectangular flat and smooth dentin adhesive surface. Each adhesive surface was divided into two parts. One side was treated with acid etching, and the other side was not. Dry, wet and overwet dentin surfaces were prepared by distilled water pipetter. SBU and PBU were used for bonding respectively. After filling, 1 mm×1 mm cylindrical rods were cut perpendicular to the dentin surface, and their micro-shear bonding strength was tested on a universal tester. The morphology of resin-dentin bonding interface was observed under scanning electron microscope. Independent sample T-test was used for statistical analysis between each two groups(P<0.05). Results ①There were statistically significant differences in the three factors of etching mode, adhesive and wetness.②In the acid etching group, there was no significant difference in bonding strength between the three moisture dentine surfaces, no matter SBU or PBU (P>0.05). In the non-acid etching group, the bonding strength of SBU on dry dentin surfaces was significantly lower than that on wet and overwet dentin surfaces, with statistical significance (P<0.05), while the bonding strength of PBU on three different moisture dentin surfaces without acid etching was not statistically significant (P>0.05). ③The bonding strength of SBU acid-etched groups was higher than that of the corresponding non-etched groups, but there was no statistical significance in wet and overwet conditions (P>0.05). The bonding strength of PBU acid etching group was higher than that of the corresponding non-acid etching group, and the differences were statistically significant (P<0.05). ④Compared with PBU, SBU could obtain higher bonding strength under the same experimental conditions, but there was no statistically significant difference in bonding strength between SBU and PBU on wet and overwet dentin surfaces after acid etching (P>0.05). ⑤The fracture modes were mainly interfacial fracture, and there was no significant difference.⑥Scanning electron microscope (SEM) showed that the resin protrusion formed by the two adhesives under the condition of acid etching was more dense and longer, and the resin protrusion extended into the dentin tubule. Under the condition of no acid etching, the resin protrusions formed by the two adhesives were sparse and short, and the resin protrusions formed by SBU were relatively more than those by PBU. Conclusion ①SBU applied to dentine surface after acid etching has low sensitivity to water, and PBU applied to dentine surface after acid etching or without acid etching has low sensitivity to water. ②SBU and PBU applied on the dentin surface after acid etching can obtain higher bonding strength than that on the dentin surface without acid etching.

Key words: universal adhesive, dentine moisture, micro-tensile strength, aid etching