Diversity loss in subgingival bacterial microbiota of children with palatal expansion: A prospective case control study

Aim: This prospective case control study assessed the impact of palatal expanders on the subgingival bacterial microbiome by 16S rRNA gene analyses over four month.Materials and methods: Sixteen children with tooth-borne acrylic palatal expanders (+BAPE) in mixed dentition were compared to sixteen untreated matched controls ( BAPE). Subgingival biofilm was sampled at baseline (t-1) before start of intervention, after one month of standardized oral hygiene with the start of intervention for cases (t0), and four months later (t+1, day of appliance). Paper-point sampling was performed and bacterial DNA was analyzed using 16S V1-V3 rRNA gene amplicon sequencing with bioinformatic evaluation.Results: The intervention had a remarkable impact on the subgingival microbiome on all taxonomic levels investigated. Relative abundances from seven genera changed significantely (p 0.85): Veillonella, Parascardovia, Capnocytophaga, Paracoccus and Leptotrichia decreased (logFC = -5.32 to -2.47) and Fusobacterium and Atopobium increased (logFC = 5.37 and 2.51, respectively). This was associated with a reduction in Shannon alpha diversity (p = 0.005) for cases at t+1 vs baseline and a shift in beta diversity (p = 0.001) at t+1 vs baseline, while controls remained stable over time as confirmed by Adonis on Bray-Curtis distances.Conclusion: Tooth-borne palatal expanders lead to diversity loss in the subgingival bacterial microbiome of children. We suggest 1) to introduce microbial ecotype screening for personalized orthodontics 2) to assess material and treatment alternatives using microbiome studies of periodontal risk outcome and 3) to perform long-term studies monitoring microbial and clinical changes after appliance removal.