Fifty patients needing non-extraction-based metallic orthodontic treatment will be divided randomly into the probiotic group and the control group. In each group, they will brush their teeth regularly while receiving orthodontic treatment. Only the probiotic group will take probiotic tablets for six months.

Clinical parameters will be assessed before and during orthodontic treatment and after 3 and 6 months during treatment.

Each subject will be examined completely to ensure eligibility before enrolling in the study. The operator will then inform them about the study's aim and ask them to provide written informed consent. Patients will receive professional scaling, polishing, and oral hygiene instruction before the research starts.

Regarding the probiotic, (PRODENTIS) is commercially available in Sweden and the USA. Probiotics prepared by Bio-Gaia AB (Stockholm, Sweden). Each probiotic tablet contains two strains of probiotic lactic acid bacteria of human origin: L. reuteri DSM 17938 and L. reuteri ATCC (PTA 5289), each at a minimum of 1 × 108 CFU per lozenge. The tablets should be stored at a temperature below 25 ◦C. Dosage instructions will be prescribed per the manufacturer's recommendations at a preventive dosage of 1 lozenge/day (after dinner and teeth brushing).

Regarding the clinical parameters, the Plaque index (Pl), the gingival index (GI), the Papillary Bleeding Index (PBI), 1977, and probing depth (PD) will be evaluated.

Inclusion Criteria:

1. Adult healthy male and female patients aged 18-25 years.

2. Patients eligible for full arch upper and lower fixed labial orthodontic appliance treatment and molar band.

3. Patients with malocclusion class I, II, or III without crowding on the anterior teeth.

4. Permanent occlusion and existence of all the upper and lower teeth (except third molars).

5. Good oral and periodontal health:

   • Probing depth < 4 mm
   • No radiographic evidence of bone loss.
   • Gingival index ≤ 1
   • Plaque index ≤ 1

Exclusion Criteria:

1. Previous orthodontic treatment history.
2. Patients with any systemic disorder that could influence periodontal conditions or response to treatment (such as hypertension, diabetes, or immunological disorders).
3. Patients were on systemic drugs, i.e., antibiotics, hypertensives, analgesics, hormonal drugs, sedatives, and anti-seizure medication, within three months before the baseline examination.
4. Patients who were allergic to ingredients of the probiotics lozenges.
5. Those undergoing periodontal treatment within three months before the baseline examination.
6. Smokers, pregnant or lactating women.
7. Regular use of antibacterial mouthwash.