This prospective cohort study is designed to evaluate the long-term effects of individualized oral hygiene education, known as Individually Trained Oral Prophylaxis (iTOP), on oral health outcomes in medical and dental students at the University of Mostar, Bosnia and Herzegovina. Participants will be randomly assigned to either an intervention group receiving personalized oral hygiene training (iTOP) or a control group. Both groups will receive professional dental cleaning and standardized oral hygiene kits. Clinical parameters will be assessed at baseline, after 3 months, and at a 2-year follow-up.

This is a prospective, two-year cohort study conducted at the School of Medicine, University of Mostar (Bosnia and Herzegovina), during the 2021/2022 and 2023/2024 academic years. The study is designed to evaluate the long-term effectiveness of a single-session oral hygiene education program, known as Individually Trained Oral Prophylaxis (iTOP), on periodontal health in medical and dental students.

- Study Population and Setting: Participants include first- and fourth-year students of medicine and dental medicine at the University of Mostar during the 2021/2022 academic year. Eligibility criteria include active enrollment and provision of informed consent. Students with systemic diseases affecting periodontal health (e.g., uncontrolled diabetes) or those using medications known to cause gingival overgrowth will be excluded.

- Study Design: Participants will be randomly assigned using a computer-generated list to either the intervention group (iTOP) or the control group. Group allocation will be concealed from examiners to minimize assessment bias. Both groups will receive professional dental cleaning and standardized oral hygiene kits at each examination point. Clinical assessments will be performed by a board-certified periodontist and a calibrated teaching assistant.

- Intervention: The intervention group will receive individualized oral hygiene instruction based on the certified iTOP methodology. This includes hands-on training in toothbrushing, interdental brush use, and flossing. A follow-up motivational session will be scheduled at 3 months. The control group will receive no structured oral hygiene education beyond standard cleaning and kit distribution. Adherence to oral hygiene recommendations will not be systematically monitored.

- Outcomes and Assessments: The primary clinical outcomes include plaque index, bleeding on probing, probing depth, and clinical attachment level. These will be measured at six sites per tooth using a UNC-15 periodontal probe and recorded on the Bern Periodontal Chart. Assessments are scheduled at baseline (2021/2022), at 3 months, and at the 2-year follow-up (2023/2024). Standardized oral hygiene kits (Curaprox toothbrushes and interdental brushes) will be provided at each time point.

- Statistical Analysis: Planned statistical analyses include both descriptive and inferential methods. Normality will be assessed using the Kolmogorov-Smirnov test. Comparative analyses will use appropriate non-parametric or parametric tests such as the Mann-Whitney U, Wilcoxon signed-rank, Friedman, Chi-square, or Fisher's exact test. All analyses will be conducted using SPSS software (version 26), with significance set at p < 0.05.

- Ethical Considerations: The study was approved by the Ethics Committee of the School of Medicine, University of Mostar (Approval numbers 01-I-1827/21 and 01-I-911/24) and will be conducted in accordance with the Declaration of Helsinki. Written informed consent will be obtained from all participants prior to enrollment.

Inclusion Criteria:

• Active enrollment as a student in either:
• First or fourth year during the 2021/2022 academic year, or
• Third or sixth year during the 2023/2024 academic year
• Enrollment verified by Faculty Administration records
• Provided written informed consent

Exclusion Criteria:

• Did not provide informed consent
• Presence of systemic conditions known to affect periodontal health (e.g., uncontrolled diabetes, immunodeficiencies)
• Use of medications known to cause gingival overgrowth, including:
• Anticonvulsants
• Calcium channel blockers
• Immunosuppressants

Deidentified individual participant data (IPD) will be available upon reasonable request to the principal investigator following publication, for research purposes only, and with appropriate data use agreements.

Deidentified individual participant data (IPD) and supporting documents will be available beginning 6 months after publication of the main results, and will be accessible for up to 5 years.

Access will be granted to qualified researchers upon reasonable request. Data will include deidentified individual participant data (IPD), study protocol, informed consent form, and statistical analysis plan. Interested researchers should contact the principal investigator via institutional email and provide a brief study proposal and data use agreement.

Clinical periodontal assessments were performed by trained examiners who were blinded to the participants' group allocation in order to reduce measurement bias.