Study protocol of a cluster randomized controlled trial on oral health promotion programs for adolescents in Iran

Abstract

To design and evaluate oral health promotion programs for high school students in underprivileged areas of Tehran Province. A multilevel intervention based on the PRECEDE-PROCEED model will target students aged 13–15 years across 18 schools in Southern Tehran, Iran. This randomized controlled trial is being conducted using multistage random sampling, 435 students in grades 7–9 will be divided into three groups: Comprehensive Intervention (CI), Less Comprehensive Intervention (LCI), and a control group. The CI group will receive interventions including group motivational interviewing for students and teachers, parental education, free oral hygiene kits, peer-supervised tooth brushing, and access to educational videos through the school learning management system. The LCI group will receive similar interventions, excluding supervised tooth brushing. The control group will follow routine oral care practices. Primary outcomes will include oral health knowledge, attitudes, and practices; secondary outcomes will comprise plaque and CAST (caries assessment spectrum and treatment) indices. Data collection will occur at baseline, and at 3- and 12-months post-intervention. Statistical analysis will assess the effectiveness of the interventions. This study aims to provide evidence for embedding oral health promotion in school curricula. Results could inform national public health strategies to improve adolescent oral health.

Introduction

Adolescence is a critical period for adopting health-promoting behaviors. Oral health behaviors are key components of public health and are often established during this period¹. Health-related behaviors established during adolescence significantly impact current and future well-being, influencing both quality of life and the health of future generations^2–4.

Schools provide a convenient and cost-effective setting for promoting health among adolescents⁵. According to the World Health Organization, school-based oral health promotion programs (OHPPs) are effective means of improving the oral health⁶. Health promotion involves a combination of educational, organizational, and political strategies designed to change both behaviours and environments, leading to better health outcomes⁷.

Educational strategies involving sustained interventions, parental and teacher engagement, and behavior change theories are effective in raising awareness, promoting healthy behaviors, and reducing plaque and decay⁸. School-based OHP initiatives such as oral health education, supervised tooth brushing, and fissure sealants are recommended. Programs combining education for children, parents, and teachers with supervised brushing and fluoride toothpaste distribution have shown success⁹. Policy efforts should integrate oral health into school health programs and promote nationwide implementation, ensuring inclusivity across all socioeconomic groups^10,11.

Iran, with a population of over 80 million, has approximately 13 million schoolchildren and nearly 7 million adolescents^12,13. Dental caries and periodontal disease are common among Iranian adolescents¹⁴. According to the national oral health survey conducted in Iran in 2016–2017, the mean DMFT (Decayed, Missing, and Filled Teeth) score among 12-year-old Iranian students was reported as 2.09.Of this total, approximately 79.6% represented decayed teeth¹⁵. Globally, 60–90% of school-age children experience dental caries¹⁶. Prevalence of cigarette and hookah use among Iranian adolescents is 56.8% and 31.1%, respectively, which is alarming¹⁷. Adolescents in lower socioeconomic conditions are disproportionately affected by oral health risk factors¹⁸. Studies on refugees and migrants report high rates of tooth decay, periodontal diseases, and poor oral hygiene¹⁹.

Using fluoride toothpaste effectively prevents cavities²⁰. Studies link insufficient brushing to higher caries risk^21,22. Peer-led strategies, such as peer-supervised toothbrushing, are grounded in Social Cognitive Theory, which highlights the role of modeling and social reinforcement in behavior change. During adolescence, peer influence is especially strong, making peers effective agents for promoting oral health behaviors²³. Studies have shown that peer-led interventions can improve oral hygiene practices, increase motivation, and are cost-effective in school settings^24,25.

In Iran, oral health programs primarily focus on children aged 6 to 12, while few studies have addressed the growing need for health promotion programs targeting adolescents^14,26,27.This study aims to develop and evaluate a practical, behavior-changing program to improve oral health among adolescents in deprived areas of the country, ultimately informing national health policy.

Methods/design

This study is a multicenter, parallel, randomized controlled trial comparing three groups: a comprehensive intervention (CI) group, a less comprehensive intervention (LCI) group, and a control group. Data will be collected at three check-ups: baseline, 3-month follow-up (short-term), and 12-month follow-up (long-term). The research protocol was approved by the Research Ethics Committees of Tehran University of Medical Sciences, School of Dentistry, code IR.TUMS.DENTISTRY.REC.1402.109. The study was registered in the Iranian Registry of Clinical Trials (https://irct.behdasht.gov.ir/; registration number IRCT20160910029765N4; registered on 24/11/2024). All methods were performed in accordance with relevant guidelines and regulations.

Primary outcomes

The primary outcomes are oral health knowledge, attitudes, and practices. Oral health knowledge, attitudes, and practices will be assessed using a validated questionnaire focusing on oral health behaviors and tobacco use^28,29.

Secondary outcomes

The secondary outcomes include CAST (caries assessment spectrum and treatment) and plaque indices. Detailed descriptions of the scoring systems are presented in Table 1^30,31.

Table 1.

CAST³⁰ and Plaque³¹ scoring system.

CAST Index scoring		Plaque Index scoring
Code	Description	Score	Description
0	Sound	0	No plaque
1	Sealant	1	Low amount of plaque detectable only by explorer
2	Restoration	2	Medium amount of plaque
3	Enamel lesion	3	High amount of plaque
4	Dentine lesion (superficial)
5	Dentine lesion (deep)
6	Pulp involvement
7	Abscess/Fistula
8	Tooth loss due to caries
9	Not recorded/Other

Participants and recruitment

Students aged 13 (grade 7) and 14 (grade 8) will be recruited from eighteen schools. These schools are located in Islamshahr and Ray. The inclusion criteria are students aged 13 and 14 years who have no systemic diseases or orthodontic brackets. Because of the 12-month follow-up period, the students’ grade at the end is 9, and their age is 15. Exclusion criteria include failure to obtain consent from either the student or their parent, as well as student transfer from the school during the study period.

To account for cluster randomization, the sample size was adjusted using a design effect of 1.4, and with a 20% anticipated attrition rate, the final sample included 145 participants per group. (total = 435 students across three groups)³².

Randomization

This study will employ a multi-stage cluster-randomized design. The unit of randomization is the school-grade level. In this region, a total of 30 schools train our target age group. The randomization process comprises two stages. First, out of these 30 schools, 18 schools (9 girls’ schools and 9 boys’ schools) will be selected for the study (refer to the sampling method). To prevent contamination between the intervention groups and the control, 3 girls’ schools and 3 boys’ schools will be randomly assigned to the control group. In the second stage, the remaining 12 schools, each with seventh and eighth grades (a total of 24 school-grades), will be allocated to two intervention groups. A random number generator will be used to produce numbers between 1 and 24, with 12 non-repeating numbers assigned to the first intervention group and the remaining 12 to the second intervention group. This process will ensure an even distribution of schools across intervention groups, allowing for a reliable comparison of outcomes.

Since all the units participating in the study are included in the study at the same time, and blinding is not possible in this study (even for data analysis, because the operator will perform the analysis herself), sequence concealment random allocation is irrelevant.

Intervention groups

This study was structured based on all nine phases of the PRECEDE-PROCEED model. Phases 1–3 were used for formative assessments to identify behavioral, environmental, and educational determinants. Phases 4–5 informed the design of tailored intervention strategies, and Phases 6–9 guided implementation and evaluation. This ensured a comprehensive and theory-based approach throughout the study. (Fig. 1)

Fig. 1.

Modified conceptual map of the study based on PRECEED (Policy, Regulatory, and Organizational Constructs in Educational and Environmental Development) model for oral health promotion of schoolchildren. The model was applied across all nine phases, from formative assessment to evaluation³⁴.

Comprehensive intervention (CI) group: The interventions in this group compromises the followings: Teaching students and teachers will be conducted through a single group motivational interview (MI) session about oral health (hygiene and tobacco use), following the strategies outlined in “ motivational interviewing in groups”³³. The session will be conducted by the researcher, who is trained in MI techniques as described in the referenced methodology. The MI session will last 45 min and will focus on enhancing motivation for healthier oral health behaviors and addressing ambivalence regarding hygiene practices, dietary habits and tobacco use and providing free toothbrushes and toothpaste; Educating parents will be conducted through a national platform named SHAD, an educational social media network used for communication between schools and families in Iran. Through this platform, parents will receive targeted educational content on oral health (hygiene and tobacco use), such as videos, articles, and infographics. To encourage parent engagement, interactive elements will be incorporated, such as online polls, question prompts, and discussion threads, where parents can share their thoughts, ask questions, and provide feedback. Regular reminders and notifications will also be sent to ensure active participation and engagement in the educational content. Examining the oral health of students by the peer group (health agents, who will be chosen through a vote by students among volunteers, and will also be trained to check for plaque remaining on their peers’ teeth) and brushing teeth under their supervision monthly; and information and educational videos for the students through the School Learning Management System (SHAD) about oral health and tobacco.

Less comprehensive intervention (LCI) group: In this group all interventions described above will be performed except for tooth brushing under the supervision of the peer group.

Control group: A routine school program that is conducted annually or as part of specific health programs, focusing solely on emphasizing the importance of oral hygiene.

Figure 1 shows the conceptual framework of the study.

Potential confounders

Socioeconomic status (SES) of families

Socioeconomic status (SES) is an important potential confounder in this study, as parental education, income level, and access to dental care can significantly influence children’s oral health outcomes. We will control SES in our statistical analyses by adjusting for it as a covariate. Additionally, stratifying by SES may also be considered to examine its differential impact across groups.

Nutritional and dietary habits

Dietary habits, particularly high sugar consumption, are a major risk factor for dental caries, which may differ between intervention and control groups. To account for this, we will collect dietary data, such as frequency of sugary snack intake, and include it as a covariate in our analysis. This will help to isolate the effect of the intervention from the potential confounding impact of dietary factors.

Access to dental services

Access to dental services can independently affect oral health outcomes, regardless of the intervention. To address this, we will document participants’ history of dental visits, fluoride treatments, and previous caries experience. This information will be included in the analysis to assess its potential confounding effect on the study results.

Oral hygiene practices at baseline

Baseline oral hygiene habits may influence the outcomes of the intervention, as children who already have good oral hygiene practices may show different results. We will assess baseline oral hygiene habits using a questionnaire or plaque index and include this information as a covariate in the statistical analysis to control for its potential impact.

Statistical analysis

The data are entered into SPSS software. The participants’ characteristics will be summarized via descriptive statistics (means, standard deviations, frequencies). Baseline data will be utilized to examine the characteristics of participants who discontinue or deviate from the trial and/or intervention. The normality of the data distribution will be checked; if the data are normally distributed, ANOVA and paired t-tests will be used to assess pre- and post-intervention measurements within each group, otherwise equivalent non-parametric tests will be employed to analyze the magnitude of change over time across the study groups, linear mixed models will be employed for continuous primary and secondary outcome variables. These models will account for fixed effects (such as the study group and time points) and random effects (including subject-specific variability). In addition, if the assumptions of normality and linearity are not met, Generalized Estimating Equations (GEE) will be used as an alternative method. Both approaches will allow us to account for within-subject correlations and ensure robust estimates of treatment effects. and if multiple tests are performed, correction methods for multiple comparisons, such as the Bonferroni correction, will be applied to control the Type I error rate. We will perform an intention-to-treat (ITT) analysis. For missing data, if assumed missing at rrandom, multiple imputation methods will be applied using SPSS or Stata.

Discussion

This study protocol outlines the design for evaluating the effectiveness of two oral health promotion programs aimed at improving oral health knowledge, attitudes, and practices among adolescents aged 13–15 years in underprivileged districts of Tehran. The publication of this study protocol will enhance its eventual usefulness and contribute to the wider application of its findings³⁵. The study aims to contribute valuable evidence on the feasibility and impact of school-based oral health interventions and provide recommendations for integrating such interventions into national curricula and health programs³⁶.

Although our study will be conducted in Iran, its findings will be consistent with peer-led oral health initiatives, for instance, in a school-based study in Tehran, Iran, by Keshmiri et al. (2021) reported that peer-led oral health education significantly improved adolescents’ oral hygiene practices and reduced their plaque index³⁷. Similarly, Bhaskar et al. (2019) in India and Ali et al. (2020) in Pakistan found that peer-led programs were effective in enhancing oral health knowledge, brushing behavior, and plaque control among adolescents^38,39. These findings support the growing body of evidence that peer-led interventions are not only cost-effective but also culturally adaptable and behaviorally impactful in LMIC settings.

A key strength of this study is its randomized controlled trial (RCT) design, which allows for the rigorous assessment of the interventions in comparison to a conventional school program. The use of a cluster randomization method, where schools-grades are randomized, minimizes the risk of contamination between intervention groups. This study provides valuable insights into the effects of different levels of intervention intensity. The study is based on the PRECEDE-PROCEED model which has been widely used for development of oral health promotion programs⁴⁰.

The primary and secondary outcomes selected for this study are comprehensive and allow for a multidimensional evaluation of the interventions. These outcomes align with key areas of focus in adolescent oral health, particularly the prevention of dental caries and the promotion of regular oral hygiene habits. The inclusion of a peer-based health assessment system in interventions is another innovative aspect of this study. Previous research has demonstrated the effectiveness of peer education in promoting health behaviors, and by involving adolescents in the evaluation of their peers’ oral health, this study aims to foster a sense of responsibility, which can reinforce behavior change²⁵. Considering the designed interventions, the results of the study also contribute to the evaluation of the effectiveness of peer education in this age group. This approach, by leveraging peer influence, offers valuable insights.

The decision to recruit students from underprivileged districts is particularly relevant, as these populations are often underserved in terms of access to oral health care and education¹⁸. The high prevalence of dental caries and periodontal diseases in such areas underscores the urgent need for effective interventions¹⁴. By focusing on these regions, this study can provide critical data on the effectiveness of school-based oral health programs in disadvantaged communities.

One limitation of the study is the potential for bias due to the lack of blinding in both the allocation process and the data collection⁴¹. Since it is not feasible to blind participants or those administering the interventions in this context, the study relies on objective outcome measures, such as clinical assessments of oral health, to minimize bias. However, it is important to note that participant and evaluator biases may still influence the results, especially in self-reported data regarding oral health knowledge and behaviors. Future studies may benefit from exploring ways to implement blinding in larger-scale interventions or the use of more objective data sources, such as clinical examinations conducted by external assessors.

Another potential limitation is the relatively short follow-up period (12 months), which may not fully capture the long-term effects of the interventions. Although a 12-month period is sufficient to observe initial changes in oral health practices and plaque levels, the sustainability of these changes beyond this time frame is an important question for future research⁴². Therefore, future studies are recommended to include longer-term follow-ups and to consider cost-effectiveness evaluations, in order to better assess the sustainability and scalability of such interventions over time.

We acknowledge that students who received parental consent may have come from families with higher awareness, which could introduce a selection bias and affect the generalizability of the results. Addressing selection bias will help improve the external validity of the findings⁴³.

The knowledge and attitude were measured solely through a questionnaire, which may not fully reflect actual behavior. While questionnaires are a valuable tool for assessing attitudes and knowledge, they may not always correlate directly with observed behaviors. To address this limitation, future studies could incorporate mixed methods, such as interviews or direct observations, to obtain a more comprehensive understanding of participants’ behaviors and attitudes. These additional methods would help reduce potential bias and provide a more accurate assessment of the impact of intervention. Furthermore, we will examine self-reported oral health behavior, which will increase the validity of the results.

Despite these limitations, the findings from this study are expected to provide valuable insights into how oral health promotion programs can be integrated into school curricula and health policies, especially in disadvantaged areas. The results will also contribute to the growing body of evidence on effective school-based health interventions and may serve as a model for similar programs in other regions or countries facing similar health disparities⁴⁴.

In conclusion, this study protocol outlines a comprehensive approach to evaluating oral health interventions in adolescents. The findings from this trial will have important implications for public health policy, particularly in the integration of oral health promotion into national school curricula and the development of interventions tailored to underserved populations. Future research should focus on exploring the long-term impact of these programs and their cost-effectiveness to inform sustainable public health strategies for improving adolescent oral health.

Abbreviations

CI

Comprehensive Intervention

LCI

Less Comprehensive Intervention

CAST

Caries Assessment Spectrum and Treatment

LMS

Learning Management System

OHP

Oral Health Promotion

PRECEDE-PROCEED

Predisposing, Reinforcing, and Enabling Constructs in Educational/Environmental Diagnosis and Evaluation - Policy, Regulatory, and Organizational Constructs in Educational and Environmental Development

RCT

Randomized Controlled Trial

SPSS

Statistical Package for the Social Sciences

Author contributions

All of the authors (Mohamad Reza Khami, Katayoun Sargeran, Fatemesadat Seyedzadeghomi) contributed in planning and designing protocol of the study and reviewed the manuscript.

Funding

Research Centre for Caries Prevention, Dentistry Research Institute, Tehran University of Medical Sciences, Tehran, Iran, grant number: 1403-2-238-72521.

Data availability

The datasets used during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The research was approved by the Research Ethics Committees of the School of Dentistry, Tehran University of Medical Sciences, code IR.TUMS.DENTISTRY.REC.1402.109, and IRCT registration number: IRCT20160910029765N4. Written informed consent was obtained from all participants’ parents before their involvement in the study.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.