This study will follow a randomised, double-blind, cross-over design. Participants will use mouth rinses containing plant extracts and/or fluoride, as well as a mouth rinse containing only water (placebo). They will use oral appliances containing sterilized enamel and dentine slabs, which will be later collected for analyses.

The cross-over design will allow participants to use all rinses, allowing for a comparison between the rinses within each individual.

This study will be made in three in situ parts. Participants will wear an oral appliance containing sterilized enamel and dentine slabs. During this experimental phase, they will use the designated mouth rinse. After this period, the investigators will remove the enamel and dentine slabs, and will also collect salivary pellicle and any bacterial biofilm forming on the participant's teeth. Participants will also donate saliva for proteomic analysis (protein profile) to verify if there are any differences in proteins in saliva to proteins in the pellicle. Throughout the whole study, all participants will use standardized oral hygiene products.

The experimental mouth rinses contain plant extracts that could interact with salivary proteins and influence the salivary pellicle and oral biofilm, thus bringing positive results against tooth (enamel and dentine) demineralisation.

Inclusion Criteria:

• Participants will be healthy young adults of both sexes, with normal salivary flow, with no cavitated caries lesions, no gingivitis or periodontal disease, no severe erosive tooth wear, and no other serious general or oral conditions.
• Participants will have signed an informed consent form.

Exclusion Criteria:

• Presenting oral diseases or conditions, such as untreated cavitated caries lesions, gingivitis or periodontitis, severe erosive tooth wear, etc.
• Participants who are under orthodontic treatment (wearing braces),
• Contraindications to the mouth rinses under study, e.g. known hypersensitivity or allergy to the investigational product,
• Participants using drugs that cause hyposalivation,
• Women who are pregnant or breast feeding,
• Intention to become pregnant during the course of the study,
• Individuals suffering from clinically significant concomitant disease states (e.g., renal failure, hepatic dysfunction, cardiovascular disease, etc.),
• Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc. of the participant,
• Participation in another study with investigational drug within the 30 days preceding and during the present study,
• Enrolment of the investigator, his/her family members, employees and other dependent persons,
• Specific exclusions for the disease under study,
• Specific concomitant therapy washout requirements prior to and/or during study participation

Mouth rinses will be placed in coded bottles, and the investigator and patients will not know to which group they belong. This is a cross-over study, where all 12 participants will use all 4 rinses.