| BackgroundsRemovable clear aligner is widely used because of its invisibility,comfort and self-removal.In order to investigate whether the effect of removable clear aligner treatment on oral health is better than fixed orthodontic treatment,a large number of studies have compared periodontal status of patients who had removable clear aligner treatment or fixed orthodontic treatment.But only a few studies paid attention to oral flora,locked the exploration of the dynamic change of bacterial structure.Saliva is the main source of samples reflecting the oral flora.The microorganisms in the saliva come from various ecological sites in the oral cavity,which can provide the overall information of oral flora.The effects caused by the treatment of removable clear aligners and fixed appliances on saliva microbial still required further study.PurposeThe purpose of this study was to investigate the changes of oral bacterial community composition and structure during the orthodontic treatment,and to compare the salivary flora between the patients with removable clear aligners and with traditional fixed appliances.Materials and methodsTwenty-one patients were included in this study refer to who met the criteria.Among them,10 subjects received removable clear aligners treatment,11 subjects received fixed orthodontic treatment.Evaluated health status before the treatment(TO),three months after orthodontic treatment(T3)and six months after orthodontic treatment(T6).Examined and recorded plaque index(PLI),gingival index(GI),probing depth and attachment loss(PD and AL),enamel decalcification(ED)on maxillary incisors(13-23).Unstimulated whole saliva was collected from each patient at three-time points,T0,T3 and T6.High-throughput pyrosequencing and bioinformatic analysis was performed based on the V3-V4 region of the bacterial 16S rRNA gene.Calculated the Observed-species,Shannon index,Pielou-e index and Pd index to estimate the alpha diversity of oral microbial.Beta diversity indices were estimated based on Weighted-Unifrac distances,Unweighted-Unifrac distances,Bray-curtis distances and Jaccard distances.Then we compared the core-microbial and relative abundance during the orthodontic treatment on difference taxonomic levels,found the salivary bacterial flora altered during the treatment.Used permutation test(pad 0.05)and wilcox test(p?0.05)screening for differential bacteria.Finally,compared the relative abundance information between and within group by the Spearman rank correlation test,analyzed the change of salivary microbial flora between different appliances with time.ResultsAs the orthodontic treatment proceed,the index of PD and AL in both group has increased,and had significant difference at T6 when compared to TO(p<0.05).No significant changes were observed in other indexes.During the treatment,the clinic indexed of clear aligner group were generally lower than in fixed orthodontic group but with no statistically significant(p?0.05),such as PLI,GI and ED.Only PD and AL index showed significant difference(p<0.05)at three months after orthodontic treatment.A total of 4036066 effective tags were obtained after sequencing,and after a 97%similarity cutoff,1560 OTUs were obtained for further analysis.The results showed that the Shannon index,Pielou-e index of fixed orthodontic group were higher than clear aligner group,the difference between the groups was statistically significant(p<0.05)in both group,but the difference between before and after treatment inter group has no statistical significance.Beta diversity analysis showed that bacterial community structures had significant difference between fixed orthodontic group and clear aligner group at T6(p<0.05).Using PCoA analysis and PERMANOVA analysis deeply compare the difference between two groups,we found that the difference in bacterial community structures between the two treatment techniques gradually increased and the difference was statistically significant at T6.(Based Weighted-Unifrac,R2=0.160,F=3.047,P=0.02*;Based Bray-curtis,R2=0.113,F=2.033,P=0.023*).The core-microbial and relative abundance analysis showed that the dominant microbes at genus level include Streptococcus,Haemophilus,Neisseria and Prevotella.And the high relative abundance microbes at species level were Haemophilus-parainfluenzae,Pseudomonas-beteli,Porphyromonas-catoniae,Gemella-haemolysans,Lautropia-mirabilis and Rothia-aeria.We totally selected 12 genus and 23 kind of species with significant difference between the two groups.Most of them had a higher abundance in fixed orthodontic group.The correlation test between the saliva flora showed that the correlation increased among the clear aligner group and fixed orthodontic group overtime,and have the most complicated network diagram at T6.Clear aligner group had more complicated network diagram than fixed orthodontic group.Conclusion1.Salivary flora diversity was not affected significantly by clear aligner or fixed orthodontic treatment during the first six months.2.As the orthodontic treatment proceed,the diversity difference between the clear aligner group and the fixed orthodontic group increased.3.As the orthodontic treatment proceed,the structure of clear aligner group and fixed orthodontic group shows difference significantly.Some bacterial related to periodontal disease such as Olsenella,Dialister and Prevotella have a higher relative abundance in fixed orthodontic group. |
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