| Background: Orthodontic treatment has been 100 years of history,with the progress of medicine,people on the oral health and beautiful demand is getting higher and higherr,orthodontic attachment wrapped in the teeth of the means of correction of teeth has been eliminated.Direct bonding technology to replace the traditional multi-band welding form,orthodontic operation greatly simplified,to bring comfort and beauty,oral orthodontic development is a milestone.But also with some negative effects,such as the brackets frequently fall off after the bonding,during the treatment or removal of the appliance around the brackets found obvious demineralization and the emergence of caries white spots,these phenomena are increasingly attentioned by orthodontists.Objective: To investigate the bonding strength and remineralization of strontium-doped nano-hydroxyapatite as filler to the enamel adhesive in vitro.Method: 1.Bonding strength test Selected 120 pieces of teeth,were randomly divided into 6 groups,each group of 20 pieces of teeth.Strontium-doped nano-hydroxyapatite with different mass ratios(0%,8%,10%,12%,14%),nano-hydroxyapatite with a certain mass ratio(10%)with the Beijing-Tianjin enamel binder composite,then the adhesives were bonded to the brackets,the shear strength(Shear strength,SS)and tensile strength(TS)were measured with 10 pieces of teeth in each group according to the requirements of universal testing machine.With the electronic universal testing machine,the loading speed is adjusted to 0.8(unit:mm / min),uniform loading to the bracket from the tooth surface,record the maximum load that bracket unloading moment load.The SS and TS of experimental groups were calculated by the maximum load / bracket floor area.2.Adhesive remnant index calculation Adhesive on the enamel surface was observed with a 10-fold magnifying glass.The improved adhesive remnant index(ARI)score was recorded,including1 point: no residual adhesive on the enamel;2 points: the amount of adhesive remaining on the enamel ?10%;3 points: 10%< the amount of adhesive remaining on the enamel? 90%;4 points: the amount of adhesive remaining on the enamel> 90%;5 points: all the adhesives are left on the enamel.Calculate the group of ARI scores.3.Remineralization test Selected 30 pieces of teeth,in the lips set aside 4mm * 4mm window area,the rest of the coating acid-resistant nail polish,were randomly divided into A,B,C three groups,with 12% strontium-doped nano-hydroxyapatite enamel adhesive,10% nanohydroxyapatite enamel adhesive,0% enamel adhesive bonding brackets respectively,then placed in saturated acid buffer demineralization,after two weeks with deionized water to clean the teeth,and placed at 37 ? artificial saliva 8 weeks.In the brackets around the enamel window parts using HVS-1000 microhardness tester,loading 200 g,maintaining 15 s,before the demineralization,demineralization and remineralization model formed of eight weeks enamel measured Vickers hardness value respectively.Each group was treated into 10 enamel blocks,dried,sprayed,and scanned under an electron microscope to observe the changes of the enamel surface around the brackets4.Statistical analysis SPSS22.0 statistical software was used to analyze the variance of the bond strength of each group,and t test was used to compare the two groups.The Kruskall-wallis H test was performed for the ARI values of the different groups.Different groups of enamel microhardness were analyzed by variance analysis.Results: The shear strength and tensile strength of 12% strontium-doped nanohydroxyapatite enamel binder were higher than those of other groups,with 10% nanohydroxyapatite enamel binder and 0% enamel binder were significantly different(P<0.05).There was no significant difference in ARI score between the two groups(P>0.05).The mineralization effect of 12% strontium-doped nano-hydroxyapatite binder was better than that of other groups.The microhardness of the three groups increased after the mineralization treatment and the microhardness of group A was the highest,which was significantly different from that of other groups(P<0.05).Scanning electron microscope showed that the demineralized enamel voids in group A were uniformly deposited with spherical particles,and only a few deposits were observed in group B,irregular in morphology and little in group C.Conclusion: Enamel adhesive with 12% strontium-doped nano-hydroxyapatite have better binding properties and significant remineralization than other groups. |
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