This multicentre randomised controlled trial aims to evaluate the efficacy and safety of the SMILETM (Siwak Method for Integrated Lifestyle Enhancement) module in improving short-term periodontal outcomes, oral hygiene behaviour, and safe siwak practice among clinical dental students. Conventional toothbrushing will serve as the control intervention.

Eligible participants will be randomly assigned to either the SMILE intervention group or the conventional toothbrushing control group. Both groups will receive professional oral prophylaxis, standardised oral hygiene education, structured training according to their allocated intervention, and digital monitoring throughout the 21-day study period.

The study will assess changes in plaque accumulation, gingival health, and bleeding on probing, as well as participant compliance, behavioural outcomes, acceptability of the SMILE module, and intervention-related adverse events.

It is hypothesised that the SMILE module will effectively improve short-term periodontal outcomes, promote better compliance with the recommended oral hygiene practice, and achieve favourable acceptability while maintaining participant safety.

The participants will be recruited from four Malaysian universities and two Indonesian universities. Individuals who meet the eligibility criteria and provide written informed consent will undergo screening, oral examination, professional oral prophylaxis and any necessary dental treatment to establish a comparable baseline oral condition prior to randomisation.

Participants will then be randomly assigned in a 1:1 ratio to either the SMILE intervention group or the conventional toothbrushing control group using a computer-generated stratified randomisation sequence. Allocation concealment will be maintained through a centralised electronic allocation system. Outcome assessors and data analysts will remain blinded to group allocation.

The SMILE intervention group will receive a structured behavioural module delivered through the SMILE mobile application. The programme includes standardised instruction on siwak preparation, brushing technique, storage, recommended frequency of use, instructional videos, supervised hands-on practice, a standardised siwak kit, and daily monitoring using the mobile application with a paper logbook available as a contingency.

Participants in the control group will receive a structured conventional toothbrushing module following the same training schedule and monitoring procedures. A standardised toothbrush kit and the study application containing toothbrushing educational materials will be provided to ensure equivalent participant support and follow-up throughout the study.

Following completion of training, participants will perform their allocated oral hygiene practice for 21 consecutive days. Adherence to the assigned intervention will be monitored using the study application or the paper logbook when required. Clinical assessments will be conducted at baseline and at Day 21 by calibrated examiners using standardised periodontal examination procedures. The study is designed to determine the efficacy of the SMILE module under controlled conditions using conventional toothbrushing as the active control intervention.

Inclusion Criteria:

1. Adults aged 18 - 24 years
2. Clinical dental students enrolled at one of the participating universities.
3. Participants with a maximum diagnosed with plaque-induced gingivitis according to the 2018 Classification of Periodontal and Peri-Implant Diseases and Conditions, without clinical attachment loss attributable to periodontitis.
4. Have adequate oral hygiene (ranging from good to fair; score from 0 to 1.9 according to Silness and Löe plaque index (1964)
5. Possess at least 28 natural teeth.
6. Able to understand study procedures and provide written informed consent.
7. Willing to comply with all study procedures, intervention instructions, and follow-up assessments.

Exclusion Criteria:

1. Using braces and dental prosthesis.
2. Presence of systemic diseases known to influence oral and periodontal health
3. Use of antibiotics for the last 3 months or any medication or known to affect oral and periodontal tissues or salivary flow
4. Moderate or high dental caries risk
5. Severe tooth malposition that may interfere with plaque assessment or oral hygiene procedures
6. Participants presenting with moderate - severe dentin hypersensitivity
7. Participants with mucosa/ gingival trauma/recession and tooth wear
8. Pregnancy or breastfeeding
9. History of allergy or hypersensitivity to any material used in the study
10. Cognitive, psychiatric, or physical conditions that may impair compliance with study procedures

Due to the nature of the behavioural intervention, participants, care providers, and investigators cannot be blinded to group allocation. However, outcome assessors responsible for the clinical examinations will remain blinded to treatment allocation. The examiners will not be involved in participant training or intervention delivery, and participants will be instructed not to disclose their allocated intervention during clinical assessments. Statistical analyses will be performed using anonymised datasets with coded treatment groups by an independent data analyst who will remain blinded to treatment allocation until completion of the primary analyses.