The goal of this clinical trial is to evaluate if the adjunctive use of an amine and zinc lactate - containing mouthrinse may give significant benefits in the home-based treatment of plaque-induced gingivitis in adolescents. The study is based on the following hypothesis: the periodontal conditions of participants affected by gingivitis will significantly benefit from the implementation of the self-performed plaque control regimen (consisting of manual toothbrush and amine and zinc lactate toothpaste) with an amine and zinc lactate - containing mouthrinse. The benefit is expected to become manifest in terms of impact on clinical periodontal parameters, ecology of the subgingival environment, patient-reported outcomes and oral-health-related quality of life. In other words, gingivitis participants implementing their self-performed oral hygiene with the investigated mouthrinse are expected to assume a closer profile (based on the outcomes listed above) to periodontally healthy subjects when compared to gingivitis participants not using the investigated mouthrinse.

One hundred fifty participants (100 adolescents with gingivitis and 50 periodontally healthy adolescents) will be selected for the study. Gingivitis patients will be asked to participate in 5 observation intervals: screening visit, study baseline, and 3 follow-up visits (3 weeks, 3 months, 6 months), while periodontally healthy controls will conclude their participation in the study within the baseline visit.

According to the randomization list, at baseline gingivitis patients will receive one of the following home-based oral hygiene regimen:

• test intervention (Gt group): manual toothbrush (meridol) and dental floss (meridol) associated with amine and zinc lactate - containing toothpaste (meridol Gum Protection) and amine and zinc lactate - containing mouthrinse (meridol Gum Protection);
• control intervention (Gc group): manual toothbrush (meridol) and dental floss (meridol) associated with amine and zinc lactate - containing toothpaste (meridol Gum Protection); All periodontally healthy subjects will be assigned control intervention.

At baseline, both gingivitis patients and periodontally healthy subjects will undergo:

• assessment of clinical periodontal parameters;
• subgingival plaque sampling for microbiological analysis;
• assessment of patient-reported outcomes (including oral-health related quality of life) using dedicated questionnaires; Gingivitis subjects will repeat the assessments at 3-week, 3-month, and 6-month follow-up visit.

The 6-month proportion of periodontally healthy participants in each gingivitis group (Gt and Gc) will be regarded as the primary outcome of the study. Changes in clinical parameters, subgingival microbial community profile, and scores related to patient-reported outcomes will be regarded as the secondary outcome measures.

Inclusion Criteria:

• systemically healthy;
• eligible for oral care provision by Regional Health Service due to low socio-economic status;
• at least 16 fully erupted teeth (excluding third molars);
• diagnosed with plaque-induced gingivitis (G) or periodontal health (PH) according to the World Workshop case definitions (Trombelli et al. 2018, Chapple et al. 2018);
• willing to participate in the study and capable to fully understand and comply with the study procedures (including questionnaire reading and filling).

Exclusion Criteria:

• pregnant or lactating;
• current smoking;
• motor and/or cognitive deficit impairing compliance with the study intervals or procedures;
• legal guardian not willing to either allow for subject participation in the study or ensure adherence with the study procedures;
• teeth with developmental defects (e.g., enamel pearls/projections);
• untreated oral lesions, including dental caries or endodontic lesions;
• fixed or removable orthodontic appliances or scheduled for orthodontic therapy with a timing not compatible with the experimental phase;
• use of antibiotics in the previous 3 months;
• use of medications that affect the size of the gingival tissues, such as phenytoin, sodium valproate, certain calcium channel-blocking drugs (e.g., nifedipine, verapamil, diltiazem, amlodipine, felodipine), and immune-regulating drugs (e.g., cyclosporine);
• conditions (e.g., Sjögren's syndrome, anxiety, poorly controlled diabetes) or medications (e.g., antihistamines, decongestants, antidepressants) that are associated with hyposalivation.

Biological samples (subgingival plaque) will be analyzed at the Section of Microbiology, University of Ferrara, Italy. However, the analysis will be conducted in a blinded fashion (no information related to patient identity and observation interval will be provided for each sample to be analyzed).