Abstract: Objective:To explore the effects of the different aging time of cured composite resin commonly used in clinic and the silane coupling agent on the bonding strength of metal brackets,and to provide reference for its clinical application. Methods: A total of 20 cuboids were made with denture resin,and 5 resin surfaces were prepared on each cuboid,then 100 specimens of resin for test were obtained.Another 5 cuboids with only one surface were prepared for observation by scanning electron microscope,and the amount of the resin surfaces was 105.After the surfaces were polished with Super-snap discs,the samples were randomly divided into 5 groups; according to different aging time,all of specimens were aged by the method of constant temperature water bath (37℃) in the artificial saliva,and five groups included instant adhesive group (A group),aged 1 h group (B group),aged 1d group (C group),aged 1 week group (D group),aged 1 month group (E group); according to the different surface treatment methods,each bonding group was divided into two groups:coating treatment with silane coupling agent after treated by 33% phosphoric acid group (A1,B1,C1,D1 and E1 groups) and 33% phosphoric acid treatment group (A2,B2,C2,D2 and E2 groups).The specimens were bonded with the metal brackets via 3M chemical cured adhesive,after 4 min solidification,the specimens were put into the artificial saliva and store for 24 h under the temperature of 37℃.The universal mechanical testing machine was used to test the shear bond strengths between the aged composite resins and the brackets,then the adhesive remnant index (ARI) of each test composite resin surface was recorded.Five observation resin surfaces were not treated and the microstructures of different aged composite resin were observed by scanning electron microscope. Results: The shear bond strengths had significant differences between various coating silane coupling agent treatment groups(A1,B1,C1,D1 and E1 groups)(P<0.01); the results of comparison between each two groups showed that the average shear bond strength in A1 group was the highest; the average shear bond strengths in B1 and D1 groups were higher than those in C1 and E1 groups(P<0.01);there were no significantly statistical differences in the average shear bond strengths between other groups(P>0.05);all the shear bond strengths in various groups were higher than the bond strength required in clinic.There were no significantly statistical differences in the shear bond strengths between various phosphoric acid treatment groups(A2,B2,C2,D2 and E2 groups)(P>0.05);only the shear bond strength in A2 group reached the shear bond strength required in clinic;the results of the comparison between each two groups showed that the mean shear bond strength in A2 group was higher than that in C2 group(P<0.05),there were no significantly statistical differences between other groups(P>0.05). There were no statistical differences in ARI of each composite resin surface between silane coupling agent treatment group and phosphoric acid treatment (P>0.05); there were signifieant differences in ARI between groups with the same aging time(P<0.05).The scanning electron microscope results showed that the distribution was nonuniform gradually with the prolongation of time. Conclusion:When the composite resin is instantly bonded with the brackets, the shear bond strength can reach the level in clinic.Sliane coupling agent can increase the bonding strength of aged composite resin to the level required in clinical orthodontic.

Key words: aging time, bonding strength, silane coupling agent, resin