Metagenomic analysis of oral microbiome around zinc oxide nanoparticle-coated mini-implants: A split-mouth trial

This study aimed to evaluate the changes in the oral microbiome surrounding zinc oxide nanoparticle (NP)-coated orthodontic mini-implants using whole-genome metagenomic sequencing and to compare the microbial colonization and clinical stability with uncoated orthodontic mini-implants.

A randomized split-mouth trial was conducted on 12 orthodontic patients requiring bilateral skeletal anchorage in the maxillary arch. Each patient received one zinc oxide NP-coated mini-implant and one uncoated implant. The implants were coated using radiofrequency magnetron sputtering. Peri mini-implant crevicular fluid samples were collected at 1 week (T1), 4 weeks (T2), and 3 months (T3) postinsertion, and the pooled sample at each time point was subjected to whole-genome shotgun metagenomic sequencing. Taxonomic and functional profiles were analyzed using Kraken and MEGAN6, with diversity indices calculated via the VEGAN R package. Stability was assessed using a 4-point semiquantitative mobility scoring.

Alpha diversity indices (Shannon and Chao1) showed no comparable differences between coated and uncoated mini-implants at any time point. Descriptive analysis of pooled metagenomic samples showed lower relative abundance or absence of peri‑implant pathogens, including Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola, and Parvimonas micra, around coated implants. Functional gene analysis revealed reduced expression of bacterial motility, chemotaxis, and ribosomal pathways in the coated group. All mini-implants remained clinically successful during follow-up. Mobility scores were significantly lower at 1 month (P = 0.04), but not at 3 months (P = 0.102).

Within the constraints of pooled metagenomic analysis, zinc oxide NP-coated mini-implants were associated with a lower relative abundance of selected peri‑implant pathogens and differences in functional pathway profiles compared with uncoated implants. Overall microbial diversity did not differ significantly between groups. Both implant types remained clinically stable, although coated implants showed reduced early mobility at 1 month. These findings should be interpreted as exploratory, and further validation through patient-level metagenomic studies is warranted.