Ecological Effect of 8% Arginine Dentifrice on Oral Microbiota of Caries-Free and Caries-active Populations

21 caries-free (CF) individuals with no clinical evidence of caries experience [decayed, missing and filled teeth (DMFT) = 0] and 21 caries-active (CA) individuals (DMFT ≥ 6) will be recruited in the clinical trial. The exclusion criteria are: smoker or former smoker, presence of any systemic disease that could alter the production or composition of saliva, treatment with antibiotics, steroids or any medication known to cause dry mouth in the last 3 months, and presence of dental prostheses or orthodontic devices. Subjects will be instructed to brush their teeth twice daily for 3 min using Colgate® Sensitive Pro-Relief® toothpaste (containing 8% arginine and 1450 ppm NaF) for 2 weeks. Volunteers are asked to refrain from brushing and flossing their teeth, eating, and drinking anything other than water for 12 h prior to sample collection visits at the end of both phases. Supra- and subgingival plaque (15 subjects in each group), saliva (21 subjects in each group), and in situ plaque samples (3 subjects in each group) will be collected before and after the treatment. Scraped plaque and saliva samples will be immediately transferred to and dispersed in sterile micro-centrifuge tubes containing 1×phosphate-buffered saline (PBS), and stored at -80 °C until needed for analysis. The in situ plaque samples will be transferred into 4% paraformaldehyde, kept under 4 °C for 16 h, and then stored in 50% (v/v) ethanol at -20 °C.