Oral Microbiome Alterations in Oral Lichen Planus Across Saliva, Dental Plaque, and Tongue Coating.

OBJECTIVE: To characterise oral lichen planus-associated oral microbiome alterations separately in saliva, supragingival dental plaque, and tongue coating. METHODS: In this cross-sectional study, samples from patients with oral lichen planus and healthy controls were analysed using bacterial amplicon sequencing. Microbial diversity, taxonomic composition, and genus-level differential abundance were compared within each sample type. RESULTS: Analyses included 47 control and 35 oral lichen planus saliva samples, 10 and 30 dental plaque samples, and 47 and 32 tongue coating samples, respectively. Significant alpha-diversity differences were observed for all four indices in saliva, three in tongue coating, and one in dental plaque. Beta-diversity differed between groups within all three sample types. Unweighted phylogenetic and presence-absence distances most consistently detected group differences, whereas abundance-weighted phylogenetic distances were not significant after correction. Unweighted phylogenetic differences remained significant after adjustment for Plaque Control Record. Descriptive taxonomic and differential-abundance patterns varied among sample types, with saliva yielding the largest number of significant taxa. CONCLUSION: Oral lichen planus was associated with microbiome alterations in all three sample types, mainly reflecting differences in microbial community membership. These sample types may provide complementary information for characterising oral lichen planus-associated dysbiosis.