Arginine is an adjunct to oral health care that has the potential to modulate the composition and activity of the microbial community of dental biofilms towards a health-related status without harmful effects for the resident oral microbiota. The aim of the study is to investigate the effects of arginine treatment compared to placebo on the composition, metabolism, and microarchitecture of biofilms grown in situ in the oral cavity of caries-active participants.

Inclusion Criteria:

• Males and females ≥ 18 years old.
• Three or more active carious lesions.
• Anatomically possible to manufacture an intraoral lower-jaw splint.
• Able to understand and follow instructions, as well as to read and sign the informed consent form.

Exclusion Criteria:

• History of allergies towards any of the ingredients in the test products
• Self-reported pregnant or nursing
• Antibiotic or anti-inflammatory medication within 90 days of the screening visit.
• Orthodontic appliances, including retainers, or removable partial dentures.
• Self-reported serious medical conditions.

Due to general data protection regulations, individual participant data will not be made available publicly. Summary data will be made available upon publication of the results.