Microbial Characteristics of the Extrinsic Black Stain in Primary Dentition

Extrinsic black stain (EBS), a pigmented dental deposit prevalent in primary dentition, is challenging to remove, tends to recur rapidly, and poses aesthetic and psychological concerns. While the microbiota plays a key role in EBS formation, the specific microbial features remain poorly understood. The aim of the study was to explore the microbial characteristics of children aged 3-5 years with the EBS.

EBS (30) and healthy (30) supragingiva plaque samples were collected for comparative analysis. The microbial features of the 2 groups were investigated using Illumina MiSeq sequencing technology and verified by quantitative polymerase chain reaction (qPCR). Potential EBS-dominant genera were isolated and identified, followed by whole-genome sequencing and bio-informatic analysis.

The qPCR results verified that Abiotrophia, Lautropia and Arachnia were significantly more enriched in the EBS group than that in the healthy group (P < .05). Four species of the above genera were isolated and identified, including E11004 (Abiotrophia defectiva), E3101(Lautropia mirabilis), E1715 (Arachnia propionica) and E10012 (Arachnia rubra). E3101 possessed the highest number of iron metabolism and biofilm-related genes among the isolates. Two genes, including 4-hydroxyphenylacetate hydroxylase (K23470) and 4-hydroxyphenylpyruvate dioxygenase (K05606), encoding key enzymes in the melanin synthesis pathway, were found in E3101, E1715 and E10012.

This study identifies E11004, E3101, E1715 and E10012 as species-level contributors to EBS, with genomic evidence implicating their potential roles in iron metabolism, biofilm formation and melanin production. These findings highlight the need for functional studies to elucidate their mechanistic roles in EBS pathogenesis.

Identifying E11004, E3101, E1715 and E10012 as key contributors to EBS offers potential targets for novel preventive or therapeutic strategies, such as antimicrobial agents or biofilm inhibitors, to reduce recurrence and alleviate the aesthetic burden in affected children.