In Vitro Study On The Prevention Of Chalky Enamel Around Brackets With Different Concentrations Of EGCG Combined With Enamel Bonding Agents

Objective:Epigallocatechin gallate(EGCG)was added to the enamel bonding agent at different concentrations and observed and measured by quantitative light-induced fluorescence(QLF),scanning electron microscopy and microhardness.The results were compared with those of the clinical light-cured orthodontic cement(GC Fuji ORTHO LC,GC)by using an in vitro PH cycle model to investigate the effect and mechanism of the prevention of enamel demineralisation and to provide a reference for the prevention and treatment of chalky plaque during orthodontic treatment.Methods:Eighty-two isolated anterior molars that were clinically extracted for orthodontic treatment were selected and the roots were removed along the enamel-bone boundary,preserving the crowns for fabrication of the samples.The △Area around the centre of the bracket was expanded by 1 mm and the buccal surface outside the open △Area was closed with black acid-resistant nail polish.Two were randomly selected as the original specimens for scanning electron microscopy to observe the normal enamel surface structure,and the remaining 80 specimens were divided into four experimental groups and one comparison group: 0 g/L EGCG,0.1 g/L EGCG,1.0 g/L EGCG and 10 g/L EGCG of enamel bonding agent and GC bonding agent,respectively,followed by an artificial PH cycle: the four groups of samples were immersed in an artificial demineralising solution for 4 hours,then rinsed three times with deionised water,dried,then placed in artificial saliva at 37°C for 20 hours,changing once a day,and repeated for a total of four weeks.Pre-and post-operative quantitative photoconductive fluorescence systems were used to take fluorescence images of each group of specimens,and ΔF,△Area,ΔQ and ΔR values of each group were measured using analysis software,and the data were statistically analysed;hardness values of randomly selected samples were measured using a microhardness tester before the PH cycle,and at weeks 2 and 4 of the PH cycle,respectively;the surface morphology of the enamel was observed under scanning electron microscopy.Results:(1)QLF test results: The differences between the baseline values of each QLF variable in the five groups before the artificial PH cycle were not statistically significant(P>0.05);the 10g/L EGCG group had the least amount of loss △F,demineralized △Area△Area,lesion volume △Q and red fluorescence △R after 2 and 4 weeks of the artificial PH cycle,while the 0g/L EGCG group had the least amount of loss △F,demineralized △Area△Area,lesion volume △Q and red fluorescence △R △Q,red fluorescence △R were the highest.The differences in fluorescence loss △ F,demineralized △ Area △ Area,lesion volume △ Q and red fluorescence △ R between groups over time were statistically significant(P<0.05);the differences in fluorescence loss △F,demineralized △Area △Area,lesion volume △Q and red fluorescence △R between groups were statistically significant(P<0.05).(2)Microhardness measurements: before the artificial PH cycle,the differences between the baseline mean microhardness values of the five groups were not statistically significant(P>0.05),and the mean microhardness values of each group at week 2 and 4 of the artificial PH cycle were statistically different(P<0.05),with the highest mean microhardness value in the 1g/L EGCG group at week 2,followed by the 10g/L EGCG,GC The 1g/L EGCG group had the highest mean microhardness value at week 2,followed by the 10g/L EGCG,GC,0.1g/L EGCG and 0g/L EGCG groups,with the same loss rate from low to high;the 1g/L EGCG group still had the highest mean microhardness value at week 4,followed by the GC,10g/L EGCG,0.1g/L EGCG and 0g/L EGCG groups,with the same loss rate from low to high.(3)Scanning electron microscopic observation results: GC group: rough surface with interrupted continuity and obvious fissures,but still visible small relatively flat enamel surface;0g/L EGCG group: part of the surface crater-like change deepened,undulating in height,showing similar to honeycomb depression,a large number of scattered pores and fissure-like structures exist;0.1g/L EGCG group: relatively flat enamel surface △Area larger than GC group,but obvious fissures were still visible and the denseness of the enamel was disrupted;1g/L EGCG group: loose surface texture,rough and irregular surface,but clearer enamel structure;10g/L EGCG group: rough surface,relatively dense texture,marked reduction in the size and number of fissures and relatively regular surface.Conclusion:(1)The values of the four indicators of fluorescence loss,lesion area,ΔQ and ΔR in the QLF assay decreased significantly as the concentration of EGCG increased,and the effectiveness of the commonly used clinical bracket bonding agent,glass ionomer GC,in alleviating enamel demineralization in the orthodontic process was verified;(2)The enamel bonding agent with 1g/L EGCG can have a good effect on the prevention of chalky enamel around the brackets without affecting the hardness of the enamel.