Objective: To evaluate and characterise the microbial compositional changes of removable dentures after interventions by comparing the efficacy of the test arm (a portable self-operated ultrasonic cleaner combined with an enzymatic peroxide-based denture cleanser solution) to the control arm (immersion of the denture in the same cleanser solution followed by conventional brushing). MATERIALS AND

Methods: A prospective, single-blind, block-randomised, two-period crossover, controlled clinical trial was conducted, involving 56 community-dwelling older adults wearing removable acrylic dentures. They were block-randomized into the test/control or control/test denture cleaning sequence. Type IIB Restriction-site Associated DNA for Microbiome metagenomic sequencing was adopted to characterize the species-resolved microbial composition for denture biofilm.

Results: For the intervention effect, the overall microbial richness in both arms was not significantly different based on the Chao 1 index (P = 0.343). However, Beta diversity analysis (Jaccard qualitative distance matrix) demonstrated significant differences in the microbial community structures between the Test and Control arms after interventions, confirmed by the Permanova test (R(2) = 0.01118, P = 0.034). Among the opportunistic pathogenic bacteria, Pseudomonas aeruginosa was detected as one of the top 30 species by relative abundance at the end of the clinical trial, and Enterobacter kobei was significantly enriched in the control arm, as determined by LEfSe analysis.

Conclusions: The microbial community of denture biofilm samples after both interventions were significantly 'shifted' and had limited numbers of opportunistic pathogens, suggesting the interventions equally effective in mitigating the overall number of pathogenic bacteria.

Clinical significance: Denture cleaning intervention using ultrasonic cleaner combined with immersion in denture cleanser solution appears to be effective in shifting the denture microbiome with reduced pathogenic bacteria among community-dwelling denture wearers.