| Background:With the development of dental bonding techniques and materials, aesthetic requirements of patients improving. It has become a trend that dental resin material takes the place of metal materials. It is said that adhesive agent plays as an important part in the resin prosthesis. During 50 years, the bonding adhesive system has undergone seven generations. Adhesive system has transformed from simple to complex while the operations has transformed from simple to complex, and then from complex to simple. In future it might be probable that the components of adheresive system will be simpler and the clinical oprations will become easier. With the rapid development of dentin adhesive agent, there are many kinds of dental dentin adhesive agent showed in the market. The property of the 7th-generation adhesives agent is not clear as the clinical and laboratory Studies are less numerous,so it is hard to say that if its adheresive effection is good without clinical evidence. Objective:We chose Single Bond 2 produced by 3M ESPE company of the USA as the representative of the fifth-generation dentin adhesive agent. Adper Prompt by 3M ESPE and XENOⅢby Dentsply are considered as the typify of the sixth-generation. And the example of the seventh-generation is G-Bond produced by the GC of Japan. By comparison of the adheresive effect of these kinds of adhesive agent, and ultrastructural changes in the dentin bonding junction, we can explain the mechanism of dentin adhesive,and provide a theoretical basis for clinical.Method:The bovine incisors were randomly divided into four groups, slice cut enamel of one proximal surface and expose dentin.Each group is operated in strict steps according to the introduction. After 24 hours, do shear stress test, according to Pa= F/S, calculate and record the shear stress of the bonding surfaces. Then classify cross-section and observe them by electron microscope. The experimental results were statistically analyzed by spss11.0.Result:(1) The shear force across each group is different. The maximum is G-Bond of the seventh-generation adhesive, for 39.4±9.5 Mpa, followed by XENOⅢof the sixth-generation for 33.6±7.6 MPa. Then the result of Single bond group is 24.5±4.2.and Adper Promp group is 24.1±6.0 Mpa. Compare Single bond 2 with Adper Prompt, P= 0.820> 0.01, shows there is no significant deviation in statistics. Compare single bond 2 and G-Bond, P= 0, shows there is significant deviation in statistics. Compare XENO III with Adper Prompt comparison, P= 0.001<0.01, shows there is significant deviation in statistics.Compare XENOⅢwith G Bond, P= 0.466> 0.01, shows there is no significant deviation in statistics. Compare Adper Prompt with G-Bond, P= 0, shows there is significant deviation in statistics. (2) Observe fracture surface of specimen by Optical microscope. Fracture of Specimens in XENOⅢand Adper Prompt group are at adheresive junction. While there is hybrid layer in one specimen of both single bond 2 group and the G-Bond group, but has no significant deviation in statistics.(3) there is evidently different among four groups when observe image through electron microscope. Demineralization in single bond 2 groups is worst, but no hybrid layer occurrs Adper Prompt group also shows strong performance of demineralization and hybrid layer can be observed. G-Bond, XENOⅢgroup has less demineralization, but the hybrid layer is clearl, resin is adhered tightly to dentinal tubules.conclusion:The mechanism of dentin adhesive among four groups is different, so the effect,and picture of electron microscopy is different. Single bond 2 is a total-etching adhesive, which can remove the smear layer and makes the deep layer of dentin demineralized. Its adhesive stress is enough in clinical. The electron microscopy shows that demineralization of detin is significantly, and no hybrid layer occurrs. Adper Prompt and XENOⅢare the sixth-generation self-etching adhesives, Adper Prompt is a strong acid-based binder, electron microscopy shows that demineralization of detin is significantly, and the bonding strength of them is satisfacted too. The cohesion of XENOⅢis strong for monomer of resin matrix penetrating deep into the dentin, because of a special component. The demineralized function of G-Bond is weak, but the adheresive effect is very strong for good penetrating that produce strong chemical bonding and mechanical micro-locking strength.
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