Potential role of Lactobacillus reuteri in the management of dental black stain: A systematic review of clinical and microbiological evidence

Dental black stain (DBS) is an atypical extrinsic pigmentation predominantly observed in youth. It is often associated with a low frequency of caries but with contemporary esthetic concerns. The aim of this systematic literature review was to evaluate the efficacy of Lactobacillus reuteri as a probiotic in the treatment and prevention of DBS. A systematic literature review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. Studies were eligible if they reported original research investigating Lactobacillus spp. primarily Lactobacillus reuteri in relation to DBS, DBS-associated microorganisms, or relevant oral microbial and clinical outcomes. Observational, clinical intervention, and in vitro or ex vivo studies were eligible, while non-original publications and studies unrelated to L. reuteri or DBS were excluded. PubMed, Scopus, ScienceDirect, EBSCO, and SpringerLink were searched from inception to May 30, 2025, supplemented by reference-list screening. Risk of bias was independently assessed by two reviewers using design-appropriate interventions, experimental models, and outcome measures; studies were grouped into epidemiological or observational, clinical, and experimental evidence, with mechanistic findings synthesized across relevant studies using a qualitative narrative approach. The findings indicate that L. reuteri strains, such as DSM 17938, ATCC PTA 5289, LR08, and LC382415, demonstrate antimicrobial efficacy against chromogenic bacteria associated with DBS, including Streptococcus mutans, Actinomyces spp., and Prevotella spp. Reuterin and cell-free supernatants have been documented in vitro to reduce biofilm formation and pathogen viability. Clinical experiments showed a decrease in the recurrence and severity of black stain with the addition of L. reuteri after scaling. Moreover, its advantageous safety profile and regulation of oral microbiota suggest its potential as a long-term biofilm management approach. Although these results are encouraging, broad generalization is limited by variations in study design, probiotic dosage, and assessment measures. Metagenomic analyses and effective future clinical trials are necessary to understand microbiological processes and create standard procedures. In general, L. reuteri is a viable non-invasive adjunct for DBS management that improves oral microbial balance without having the negative side effects of traditional antimicrobials.