Microbial Environmental Analysis of Orthodontic Homeostasis in the Mandibular Anterior Decompensation Zone During Pre-orthognathic Orthodontic Treatment in Skeletal Class III Patients

Objective: To characterize microbial community structure, diversity, and composition in the mandibular anterior decompensation zone during the late, stabilized phase of presurgical decompensation in skeletal Class III patients. Methods: In this prospective study, we analyzed eighteen gingival crevicular fluid samples from six adults (3 males, 3 females; age 21.8 ± 1.6 years) undergoing orthognathic surgery for severe skeletal Class III malocclusion (ANB: -5.6 ± 0.8°). Samples were collected from mandibular central incisors at three intervals within one month, near the completion of presurgical decompensation. Microbial profiles were generated using 2bRAD-M sequencing to assess alpha and beta diversity, taxonomic composition, and KEGG functional pathways. Results: The subgingival microbiome demonstrated remarkable stability during the final month of orthodontic decompensation. Both alpha diversity (Chao1, Shannon, Simpson; Kruskal-Wallis, P > 0.05) and beta diversity remained unchanged across all time points. The community was consistently dominated by phyla (Firmicutes, Bacteroidetes) and commensal genera ( Streptococcus, Prevotella ) characteristic of oral health, with a low abundance of inflammation-associated taxa. The only notable fluctuations were minor and transient variations within the top-10 KEGG functional pathways. Conclusions: Following orthodontic decompensation, the mandibular anterior region harbors a stable, diverse, and anti-inflammatory microbiome consistent with oral health. This finding validates the clinical importance of ensuring biological stability prior to orthognathic surgery. Furthermore, this work lays the groundwork for using microbial markers to optimize treatment timing and assess surgical readiness.