Optimal storage time and temperature of human oral samples to minimize microbiome changes: A scoping review

Improper storage times and temperatures negatively impact the quality of biospecimens with oral microbiomes. This study aimed to determine the optimal storage time and temperature for maintaining the integrity of human dental plaque and saliva samples' microbial profiles. A comprehensive search yielded 5433 studies, with 12 meeting inclusion criteria. The number of studies on the storage time and temperature for plaque or saliva samples was extremely limited, with large variability in study designs and analytical tools. The best approach for dental plaque and saliva samples was to immediately freeze fresh specimens at - 80 °C or lower until DNA extraction, with a recommended storage time not exceeding 1-2 years, regardless of temperature. Checkerboard DNA-DNA hybridization-based studies suggested dental plaque storage at - 20 °C for 6 months, but a shorter duration was advised. Based on 16 S rRNA gene sequencing studies, dental plaque samples could be stored at - 80 °C for 6 months in 75 % ethanol or Bead Solution. Dental plaque and saliva samples could be stored at room temperature for 1-2 weeks without significant microbiome changes if stored in appropriate media. Further well-designed randomized controlled studies with longer-storage duration are necessary to establish more definitive guidelines.