Oral dysbiosis systematically develops during orthodontic treatment [35][36]. Orthodontic appliances interfere with oral hygiene procedures and cause biofilm to accumulate, creating new retention zones, even in subjects who maintain correct oral hygiene [37]:

• A group benefiting from intensive personalised prevention
• A "conventionally monitored" group, with no personalised prevention. The hypothesis is that personalised prevention prevents dysbiosis from taking hold. If this hypothesis is confirmed, the concept could be extended to all patients, beyond orthodontics.

Based on the "biological signature" (microbiological and immune), a "risk profile" of patients could be defined, making it possible to better personalise the prevention message, the method applied and the frequency of follow-up. The aim would be to rebalance dysbiosis through a personalised prevention approach tailored to the profile defined.

It was decided to explore this hypothesis initially with orthodontic patients because they are "captive", i.e. in the course of treatment requiring regular visits. Prevention is aimed first and foremost at healthy patients, with the aim of maintaining them in good health. The project focuses on young patients undergoing orthodontic treatment

Inclusion Criteria:

• Patients aged 12 to 20 (permanent dentition) requiring fixed orthodontic treatment.

Exclusion Criteria:

• Tobacco;
• Overcrowded restorations, untreated caries,
• lack of tooth mineralisation;
• Medical pathologies;
• Known immunodepression (congenital or acquired);
• Taking a treatment that may induce general immunodepression;
• Taking a probiotic;
• Taking a concomitant treatment that may interact with oral health