Objectives: The objectives were to quantify the contributions of internal (self) and external (familial) sources to the recolonization of the bacterial content of the subgingival plaque following professional prophylaxis and assess the effect of close-contact activities on modifying this contribution. Materials and Methods: Families, each consisting of at least one preschool-aged child and at least one sibling, were recruited for this interventional cohort pilot study. Microbial samples were collected from various oral sites, including saliva, buccal mucosa, tongue, supragingival plaque, and subgingival plaque in all family members. Following the child's oral prophylaxis, subgingival plaque samples were collected one week later. DNA from these samples was extracted and sequenced using the 16S rRNA gene and estimation of the sources were quantified using Bayesian source tracking models. Additional analyses using generalized linear mixed models, Phylofactorization, and Spearman correlations. Statistical significance was set at p<0.05. Results: Child's own subgingival plaque was the primary source of recolonization, contributing 63.7% to the microbial community one-week post-prophylaxis. Siblings contributed approximately 8%, a contribution significantly higher than that from parents, who contributed around 3% each (p<0.05). The analysis revealed a statistically significant positive correlation between the number of siblings and their bacterial contribution to the child's subgingival plaque. Several close contact activities between parents and children were statistically associated with higher contribution (p<0.05, Spearman correlation). Additionally, 110 bacteria were statistically significantly different in their internal contribution compared to external, after accounting for household association, sample type, and family members (p<0.05, Phylofactor) Conclusion: The findings challenge the traditional focus on parent-child transmission of oral microbes, highlighting the importance of studying families as a whole.

The authors have declared no competing interest.

Oral Health for Children, Youth, and Families Fund (OHCY-02)

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Ethics committee of The University of Alberta gave ethical approval for this work.

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All data produced in the present study are available upon reasonable request to the authors and will be published in NIH SRA once the publication gets accepted by the journal.