Impact of removing fixed orthodontic appliances on oral microbial dysbiosis: A longitudinal study and metagenomic sequencing analysis

Abstract

Objective:

To investigate the impact of appliance removal on oral microbial diversity, composition, and abundance using metagenomic sequencing. It aims to identify the core microbiome and assess changes between mid-treatment and 2 weeks after debonding to understand the relationship between orthodontic therapy and oral health better.

Methods:

This longitudinal cohort study recruited 26 patients undergoing fixed orthodontic treatment between January 2022 and June 2023. Saliva samples were collected at two predefined time points: mid-treatment (T0, defined as before appliance removal) and 2 weeks after debonding (T1). Microbial DNA was extracted and the V1–V3 hypervariable regions of the 16S rRNA gene were sequenced using Illumina NovaSeq. Bioinformatics analysis was performed using QIIME and the SILVA database to evaluate microbial diversity and composition at T0 and T1. Beta diversity metrics and statistical tests, including PERMANOVA and Wilcoxon signed-rank tests, were applied to identify significant differences (P < 0.05). Effect sizes with 95% confidence intervals (CIs) were reported.

Results:

The analysis revealed significant shifts in microbial diversity and composition between T0 and T1. A total of 189 species across 63 genera were identified, with Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, and Fusobacteria as dominant phyla. Genera such as Fusobacterium periodonticum (↑ 12.4%, 95% CI = 10.1–14.7) and Veillonella parvula (↑ 9.8%, 95% CI = 7.6–11.3) increased after debonding, while Prevotella melaninogenica (↓ 10.2%, 95% CI = 8.1–12.0) and Rothia dentocariosa (↓ 7.9%, 95% CI = 6.3–9.2) decreased. Beta diversity analysis confirmed a statistically significant microbial community shift (P < 0.05).

Conclusion:

This study demonstrated significant microbial shifts between mid-treatment and 2 weeks after debonding, including increases in potentially pathogenic genera and alterations in the core microbiome. These findings indicate microbial changes persist for at least 2 weeks after appliance removal. Further research with pre-treatment baselines and extended follow-up is required to better define the long-term trajectory of these changes.

Plain language summary

Braces and oral health: How the mouth’s microbiome changes during and after orthodontic treatment

Why was the study done? When people wear fixed braces, food can get trapped around the wires and brackets, making it harder to keep teeth clean. This can allow harmful bacteria to grow. Most studies only check bacteria before and during treatment. We wanted to find out what happens after braces are removed. What did the researchers do? We collected dental plaque samples from patients while they were still wearing braces (mid-treatment) and again 2 weeks after their braces were removed. We used a genetic test called 16S rRNA sequencing to see which bacteria were present and how the overall community changed. What did the researchers find? The types and amounts of bacteria were different between mid-treatment and after braces came off. Some harmful bacteria linked to gum disease and tooth decay were still more common even after the braces were removed. What do the findings mean? The results show that braces may cause lasting changes in mouth bacteria that do not go away immediately after treatment. Dentists should encourage patients to pay extra attention to cleaning their teeth after braces are removed. Future studies may test ways, such as probiotics, to help restore a healthy balance of bacteria.