| ObjectiveInterproximal enamel reduction(IER)has been widely used in clinical dental treatment,especially in orthodontic therapy.IER is often used to solve dental crowding,level the curve of Spee,and correct the index of Bolton.However,IER can also bring some side effects which limit its use and development,such as tooth sensitivity,defect of dental morphology,irreversible damage of dental pulp,recession of periodontal tissues and increase of caries susceptibility risk.All these complications have raised clinicians' attention.The purpose of this investigation was to explore whether there are differences of caries susceptibility among a group of extracted premolars which have been removed different amount of interproximal enamel.MethodsPart OneEvaluation of caries susceptibility during different IER groups in bacteria based cariogenic modelIn vitro cariogenic model was built by Streptococcus mutans(S.mutans)and extracted premolar teeth.After IER,the initial surface microhardness(SMH)of the enamel blocks were measured using a Vickers diamond indenter under a 50-gram load for 15 s.Next,all the enamel blocks were immersed in the bacterial suspension for 10 d,15d,20 d respectively.After this procedure,enamel SMH values measured with same static load and time again(SMH).Then,confocal laser scanning microscopy(CLSM)was used to detect whether there are differences in caries susceptibility among different IER groups.At last,the outcome of SMH values and CLSM were collected and analyzed if there is statistical significance among different groups.Part TwoEvaluation of caries susceptibility during different IER groups in chemical demineralization solution cariogenic modelPartially saturated acid buffer demineralization system was build in vitro.After IER,the initial surface microhardness(SMH)of the enamel blocks were measured using a Vickers diamond indenter under a 50-gram load for 15 s.Next,all the enamel blocks were immersed in the demineralization solution for 5d,10 d,15d,respectively.After this procedure,enamel SMH values measured with same static load and time again(SMH).Then,confocal laser scanning microscopy(CLSM)was used to detect whether there are differences in caries susceptibility among different IER groups.At last,the outcome of SMH values and CLSM were collected and analyzed if there is statistical significance among different groups.Results1.There is no significant difference(p>0.05)in SMH values among different IER groups which had been reduced different amount of interproximal enamel neither in bacteria based cariogenic model nor in chemical demineralization solution cariogenic model.2.Comparison of SMH values of enamel blocks before and after demineralization showed significant difference(p>0.05)both in bacteria based cariogenic model and chemical demineralization solution cariogenic model which indicated that there are changes of SMH values of enamel blocks sample.3.There is no significant difference(p>0.05)in SMH values in 10 d,15d,20 d groups(bacteria based cariogenic model)and in 5d,10 d,15d groups(chemical demineralization solution cariogenic model)which indicates that process time does not matter.The results of three factors analysis of microbial-based cariogenic model,different cariogenic time in chemical cariogenic model,and different amount of interproximal enamel reductionshowed that there was no significant difference in SMH values between different amount of enamel reduction in different environments and process time(P>0.05)(p=0.875 R2=0.902).4.There was no significant difference in total f1uorescence(TF)of CLSM in same process group(p>0.05).However,the results of different process groups with same amount of IER showed significant difference(p<0.05).The results of three factors analysis of microbial-based cariogenic model,different cariogenic time in chemical cariogenic model,and different amount of interproximal enamel reduction showed that there was no significant difference in fluorescence values between different amount of enamel reduction in different environments and process time(P>0.05)5.There was no significant difference in average f1uorescence(AF)in same cariogenic model and same process time with different amount of IER.And there was significant difference in AF in different cariogenic model and different process time with same amount of IER.The results of three factors analysis of different cariogenic time in microbial-based cariogenic model,different cariogenic time in chemical cariogenic model,and different amount of interproximal enamel reduction showed that there was no significant difference in AF between different amount of enamel reduction in different environments and process time(P>0.05).6.For group microbial-based cariogenic model-10 d and group chemical cariogenic model-5d,there was no significant difference in area of f1 uorescent lesion(A)with different amount of IER.Howerver,for group microbial-based cariogenic model-15 d,20d and group chemical cariogenic model-10 d,15d,there was significant difference in A with different amount of IER.And there was significant difference in A in different cariogenic model and different process time with same amount of IER.The results of three factors analysis of different cariogenic time in microbial-based cariogenic model,different cariogenic time in chemical cariogenic model,and different amount of interproximal enamel reduction showed that there was no significant difference in A between different amount of enamel reduction in different environments and process time(P>0.05)Conclusion1.The SMH values of enamel blocks decreased and initially artificial caries lesions were seen in samples after demineralization caused by chemical solution or organism.2.When the amount of interproximal enamel removal are 0.0mm,0.2mm,0.3mm,0.4mm,there is no difference of caries susceptibility between treated teeth in microbial-based cariogenic model.Samples in this study support that,within the range of 0.0-0.4mm,with an increasing of the amount of interproximal enamel removal,there is no increasing of caries risk.3.When the amount of interproximal enamel removal are 0.0mm,0.2mm,0.3mm,0.4mm,there is no difference of caries susceptibility between treated teeth in chemical cariogenic model.Samples in this study support that,within the range of 0.0-0.4mm,with an increasing of the amount of interproximal enamel removal,there is no increasing of caries risk. |
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