Children with incomplete anthropometric or dental assessment data were excluded from the analysis. The missing information in the questionnaire was removed from the list. Among the 1864 children aged 7-12, 50.59% were boys (943) and 49.41% were girls (921) (Fig.1). The chi-square test was used to analyze the relationship between demographics and the prevalence of dental caries (Table 1).
There was no significant difference in the incidence of dental caries among primary teeth, permanent teeth, and mixed dentition between males and females (χ 2 were 0.58,1.21,0.14 respectively, P > 0.05). There were significant differences among different BMI groups and age groups (P < 0.05). The incidence of caries was about the same in different genders. In the BMI group, the incidence of caries of primary teeth and mixed dentition in overweight and obesity groups was lower, but that of permanent teeth was higher. The incidence of permanent teeth caries increases with age, and 21.36% of 12-year-old children have permanent teeth caries.
The relationship between related factors and the decayed-missing-filled index of primary teeth, permanent teeth, and mixed dentition is presented in Table 2. There were significant differences in dmft between groups with different dietary structures, frequency of consumption of cookies and cake, candy and chocolate, carbonated beverage and juice, parents' educational level, exercise frequency, and sedentary habit (P<0.05). There was no significant difference in DMFT among groups with different frequencies of candy and chocolate intake (P>0.05). Intake frequency of cookies and cakes, carbonated beverages and juice, parents' education level; exercise frequency; and sedentary habits were significantly correlated with DMFT (P<0.05).
There were statistically significant differences in dmft and dmft+DMFT among different BMI groups (P<0.05), and dmft and dmft+DMFT decreased with the increase of BMI classification. There was no significant difference in DMFT among all groups (F=2.49, P> 0.05) (Table 3).
Multiple linear regression analysis was performed on dmft, DMFT, and dmft+DMFT (Table 4). Because of the high correlation between biscuit cake and candy chocolate intake frequency, they were not initially included in the same regression model to avoid multicollinearity.
The children with low BMI index and parents' educational level had significantly higher dmft(p=0.001, p<0.001). Children with high cookie and cake, sugar drinks consumption frequency and high exercise frequency had significantly higher dmft (p<0.001,p<0.001,p=0.001). The results of Model 2 show that those with a high BMI index have significantly higher DMFT (p=0.004). The result of model 3 shows that the relationship between dmft+DMFT and each variable is the same as in model 1.
We randomly sampled 40 children and divided them into four groups:A0: high caries(HC)+obese(n=10),B1:Carries-free(CF)+obese(n=10),C2:HC+non obese(NO) (n=10), D3: CF+NO(n=10).
The results of 40 saliva samples and 40 stool samples showed that Firmicutes were more in the obese group than in the normal group, and Bacteroides were less. The relative abundance of salivary level showed that the content of Prevotella was the lowest and that of Streptococcus mutans was the highest in the obese caries group. The relative abundance of fecal genus level showed that Bacteroides was the highest in the normal group, Prevotella was the lowest in the caries group, Prevotella was the highest in the caries group, and Bacteroides were less in the obese and caries obese groups than in the normal group (Fig.2).
There was a statistically significant difference in the Simpson index of Alpha diversity in saliva samples (p=0.077), but no statistically significant difference in fecal samples (p=0.64). Anosim analysis showed no significant difference in saliva and fecal samples between groups (p=0.496, p=0.272). The five dominant bacteria in saliva and fecal samples were selected for intra-group comparison. The results showed that Prevotella was statistically different between the saliva and feces samples.
Stacked bar plots of relative abundances at the phylum level demonstrated differences in oral and gut microbiota among four groups (Fig. 2A). Firmicutes, Bacteroidota, Proteobacteria, Actinobacteriota and Fusobacteriota were predominant
phyla in saliva, and Firmicutes and Bacteroidetes were predominant phyla in feces of all groups. At the genus level, Prevotella,Streptococcus,Haemophilus,Neisseria,Veillonella were predominant in saliva; Bacteroides,Faecalibacterium,Bifidobacterium,Agathobacter,Prevotella were predominant in feces.
Analyses of alpha (a)-diversity demonstrated that there was a statistically significant difference (p < 0.05) in the chao1 index between the CF+Obese and HC+Obese groups, and between the CF+NO and HC+Obese groups in saliva samples.
In feces samples,there was a statistically significant difference (p < 0.05) in the shannon index between the CF+Obese and HC+Obese groups,and between the HC+NO and HC+Obese groups.(Fig. 3A).
PCoA was performed to assess beta (b)- diversity of the microbiota (Fig. 3B). Bray-Curtis distance matrix demonstrated has no statistical difference (p=0.473,p=0.25) in b-diversity of oral microbiota and gut microbiota among four groups (Fig. 3C).
we selected 10 genera which ranked at the top of the total genera and analyzed the predominant members in each group. Comparing the saliva relative abundance in each group, we found that Prevotella was present at a lower level in CF+NO than HC+NO and HC+Obese group (p< 0.05; p< 0.05),Streptococcus was at a higher level in HC+NO than CF+NO and CF+Obese (p< 0.05; p< 0.05,Figure 4A). Among gut microbiota in each groups, Faecalibacterium in CF+NO was higher than CF+NO and CF+Obese (p< 0.01; p< 0.05). Bifidobacterium in CF+NO was lower than HC+NO and CF+Obese (p< 0.05; p< 0.05). Prevotella in HC+Obese was higher than CF+Obese and CF+NO (p< 0.05; p< 0.001), that in HC+NO was higher than CF+NO (p< 0.05, Figure 4B).
Source Tracker analysis explored the ectopic colonization of oral microbiota in the gut, showing one in HC+NO (No. 32) and one in CF+Obese (No.1) had a fraction of their gut microbiota which had originated from the oral cavity in Figure 5.