Introduction

Dental caries influences the social life and well-being of people and has a great impact on the quality of life. In children, untreated caries has more negative impacts as it influences social life, school attendance, speech, and self-esteem [1, 2]. Oral health improvement is recommended through community programs, especially in school-aged children. It is necessary to promote awareness of caries risk factors, especially in developing countries. Supervised toothbrushing programs in the school setting has been well-documented as an effective method to improve the oral health of children [1, 3].

Schools are considered as an important setting to transfer information to children and their families as they offer an efficient and effective way of reaching over one billion children worldwide [1]. The school setting makes it possible to detect oral health problems at early stages and deliver care [4]. Many studies, including a review by Cooper et al., recommend brushing in school [5]. In addition, a large body of evidence demonstrates the effectiveness of fluoride delivered in various forms such as varnish, gel, toothpaste, etc. to prevent dental caries [6, 7]. The guidelines recommend that supervised toothbrushing should start from approximately 6 months of age up to the age of 7 [8].

A key component of supervised toothbrushing programs is ensuring plaque removal effectively via brushing twice daily using fluoride toothpaste under the supervision of a parent/caregiver [8]. The supervised toothbrushing technique is highly recommended at the time of eruption of permanent first molars at about six years of age. Most parents may not be aware of tooth eruption and neglect the plaque removal [9]. In this regard, the bucco-lingual technique is considered an effective method in plaque removal, especially when supervised by parents [10].

There are common indices to measure dental caries in the community-based surveys such as the DMFT/dmft index [11] although this index does not reflect the consequences of untreated dental caries, including pain and infection. Due to limitations of the newly developed indices such as the ICDAS [12] and PUFA/pufa [13], a new index was developed by Frencken et al. in 2011 [14] to measure a wide range of caries from non-cavitated to advanced cavitated lesions as well as the clinical consequences of caries. Considering the new concept of caries management, it is important to record a wider range of caries from non-cavitated to cavitated lesions. This is more important in developing countries where service delivery is limited and caries mainly remains untreated in children [15].

According to a national survey in 2012, the prevalence of tooth decay is high in Iranian children. The mean dmft/DMFT index was 5.16 (SD = 0.38) in 6-year-old children, and only 13% of children were caries-free in this age group [15]. There is also evidence of a wide spectrum of dental caries in Iranian children [16], indicating the importance of the management of non-cavitated lesions as well as service delivery to the high-risk children. Since no study has evaluated the oral health status of Iranian children, especially following oral health promotion programs using detailed indices, the purpose of the present study was to evaluate the impact of an oral health promotion program, including supervised toothbrushing, on the oral health status of schoolchildren aged 6–7 years old in Tehran, Iran.

Materials and methods

This study was a parallel-arm, examiner/statistician-blind, one-year follow-up of a community-based randomized controlled trial of an oral health promotion program including oral health education and supervised toothbrushing. This study was conducted on schoolchildren aged 6–7 years old in 19 educational districts of Tehran, Iran.

Sampling

This study was a one-year follow-up of a previously described community trial of school children from February of 2016 to March 2017 (methodology explained elsewhere) [17]. After considering schools as clusters, randomization applied at the class level, and one class was selected randomly from each school. Thus, 12 schools/classes were selected in each arm of the study. Blinding was done and the participants, the statistician, and the examiner (PKH) were not aware of the allocated group [16]. We calculated the sample size using the formula based on comparison of two proportions in the case and control groups. This proportion was the percentage of children with pulp involvement calculated as 0.3 based on the pilot study of 20 students. Accordingly, the sample size was calculated 720 subjects, 360 subjects in each group, with a power of 80%, α = 0.05, β = 0.2, loss to follow-up of 20%, and design effect of 1.5. The framework of the study is presented in (Fig 1). The inclusion criteria were schoolchildren aged 6–7 years old that went to public schools and their parents gave informed consent. In addition, the children that had allergies to fluoride, physical disability, systemic diseases, or dental emergencies were excluded.

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Fig 1. Overview of the study at baseline and one-year follow-up according to the CONSORT flow diagram.

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Intervention

Theoretical session.

In the intervention group, the parents/caregivers of the children were invited to participate in a one-day workshop on supervised toothbrushing according to the World Health Organization (WHO) format [18] that was delivered to parents using a PowerPoint presentation. In addition, due to the importance of the permanent first molars, the professional buccolingual technique was presented using a video clip followed by a question and answer session. A free-of-charge package containing a toothbrush and fluoride toothpaste (1000 ppm) and a weekly guide was also given to the parents for use at home (Fig 2).

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Fig 2. Weekly guide of supervised toothbrushing for children for use at home.

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The content of the parents’ workshop included the order of the eruption of deciduous and permanent teeth, the position of the first permanent molar teeth, the concept of dental plaque and dental caries, toothbrushing technique (particularly the buccolingual technique for the first permanent molars), the importance of supervised toothbrushing, proper nutrition, and fluoride and fissure sealant therapy. Finally, a pamphlet and a parent supervision package were given to the parents. In addition, an overview of the etiologic factors of tooth decay was presented to children in the classroom including the importance of toothbrushing, proper brushing technique, fluoride use, and sugar consumption. The educational intervention package for children and parents was repeated twice in the period of one-year after the initial examination.

Practical session.

In the intervention group, after coordinating with the teaching staff, the students were taught how to brush properly including the first permanent molars under the supervision of the main researchers (AB, AP) in the school setting in groups of 6–8 children. A free toothbrush with a pea-sized amount of fluoride toothpaste was given to each student. It is noteworthy that all children in both intervention and control groups received varnish fluoride (22,600 ppm) biannually as part of the national fluoride program offered by the Ministry of Health and Medical Education (MOHME).

The examiners were calibrated, and dental caries was measured according to the CAST index [14] by the first examiner (AB) calibrated by an expert (AP) (inter-examiner kappa: 89.8, intra-examiner kappa: 91.2). In addition, one year after the intervention, the examination was repeated by another dentist (PKH) that was blind to groups and was calibrated by an examiner (AB) (Kappa = 87.68%).

Questionnaire.

A previously validated questionnaire [19] was used to assess oral health related knowledge, attitude, and self-reported behavior of parents. The questionnaire had three sections, including: A) parents’ knowledge of etiologic factors of dental caries, cariogenic diet, importance of brushing and its frequency, and using fluoride (9 questions). B) parents’ attitude about the importance of dental caries and its prevention (6 questions), and C (a) parents’ self-reported behavior including the frequency of brushing, using fluoride toothpaste, and consuming sugary snacks and drinks (3 questions) and C (b) children’s oral health related behavior including brushing frequency, using fluoride toothpaste, and having sugary snacks and drinks (3 questions).

In the knowledge section, correct answers scored one and incorrect answers scored zero. In a Likert scale, correct answers included “I strongly agree” and “I agree” for questions with a positive answer and “I disagree” and “I strongly disagree” for questions with a negative answer. Then, the sum score of the questions (0 to 9) was calculated for each subject. In the attitude section, a 5-point Likert scale from “I strongly agree” to “I strongly disagree” was dichotomized and the total score was calculated (6 to 30). In the self-reported behavior section, the sum score of questions (0 to 6) was calculated for each person. Parents’ and children’ behavior questions included three questions. The correct answers scored 1 vs. 0 for incorrect answers. Then, the sum score (0 to 3) was calculated for each person.

Results

In the community trial, 739 children aged 6–7 years were included at baseline of whom 593 were re-examined after one year (response rate = 74%). In addition to clinical data, 549 children returned the completed questionnaire on oral health-related knowledge, attitude, and self- reported behavior of parents (Table 1).

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Table 1. Demographic characteristics of study participants in control and intervention groups in one-year follow-up.

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Questionnaire

At baseline, the sum score of the parents’ oral health-related knowledge, attitude and behavior were compared as the (mean and standard deviation of the sum score) between the intervention and control groups (6.76±1.89 vs. 6.92±1.59, 5.04±1.33 vs. 5.31±1.05, and 2.59±0.64 vs. 2.60±0.62, respectively), indicating no significant difference. In addition, the children’ oral health behavior (mean and standard deviation of the sum score) was compared between the intervention and control groups (2.12±0.82 vs. 2.11±0.80). Table 2 shows changes in the mean score of the parents’ oral health related knowledge, attitude and self-reported behavior compared to baseline in the intervention and control groups after one year according to the GEE analysis. There was improvement in the intervention group compared to the control group; however, the changes in the parents’ attitude and children’s behavior were marginally significant.

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Table 2. Evaluation of changes in the mean score of oral health knowledge, attitude, and practice in one-year follow-up compared to baseline in control and intervention groups.

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Dental caries according to CAST index

Table 3 shows a CAST score ≥ in primary molar teeth in the intervention and control group at baseline compared to the one-year follow-up. According to the GEE analysis, after considering the confounding effect of time, significantly more children in the control group had deciduous molars with a score ≥ compared to the intervention group (OR = 1.79; 95% CI: 1.17–2.73, p = 0.007). The caries status of children in the control and intervention groups in primary and permanent dentition at baseline and one-year follow-up according to the CAST index demonstrated in Fig 3.

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Fig 3.

Caries status according to the CAST index in the primary and first permanent molars in the control and intervention groups at baseline (A and B) and 1-year follow-up (C and D).

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Table 3. Comparison of changes in caries status of primary molar teeth in one-year follow-up between intervention and control groups according to the CAST index.

https://doi.org/10.1371/journal.pone.0284366.t003

Oral hygiene

The oral hygiene status of the children measured according to the OHI-S index. At baseline, the mean and standard deviation of the oral hygiene score was 0.49±0.03 and 0.48±0.04 in the intervention and control group respectively, indicating no significant difference [16]. The changes (Δ) of the OHI-S score in the post-test evaluation in the one-month follow-up are reported elsewhere [17]. After one-year, the Δ OHI-S was 0.59±0.06 and 0.85±0.04 in the intervention and control group, respectively (p = 0.01). The comparison between baseline, one-month follow-up, and one-year follow-up of oral hygiene status measure according to Δ OHI-S presented in (Fig 4). The results of the GEE analysis, after adjustment for the confounding effect of time, showed a significantly higher OHI-S score in the control group compared to the intervention group (B = -0.27, 95% CI: -0.45 –-0.08, p = 0.005). Accordingly, the GEE analysis showed improved oral hygiene status in the one-year follow-up.

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Fig 4. The mean OHI-S score in children at baseline, one-month follow-up, and one-year follow-up in intervention and control groups.

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Discussion

The present study evaluated the one-year impact of an oral health promotion program including parents’ education and supervised toothbrushing on oral health status of schoolchildren aged 6–7 years old. One year after implementing the program, the changes in the parents’ attitude and children’s behavior were marginally significant in the intervention group. According to the CAST index, there was less caries in deciduous molar teeth in the intervention group compared to the controls. In addition, a significant improvement observed in the oral hygiene status of children according to the OHI-S index in the intervention group compared to the control group. An improvement observed in the level of oral health related knowledge and self-reported behavior of parents that received the intervention package compared to the controls although the difference was not significant.

In the present study, evaluation of the caries status based on the CAST index showed that the percentage of caries in primary molars (CAST score ≥ 3) was significantly lower in the intervention group compared to the control group one year after the initial examination and receiving the educational interventions. Our findings are consistent with the results of longitudinal studies by Peterson et al., [20] and Tai et al., [21] that reported caries reduction based on the DMFT index in the intervention group receiving an educational package compared with the control group. However, they are in contrast to the results of a review study by Stein et al. in 2018 that did not find any long-term evidence regarding the effectiveness of educational interventions in caries prevention [22]. Moreover, in 2015, Jaime et al. reported that more subjects in the experimental group had higher knowledge of dental caries and declared that they used dental floss daily, but there was no significant difference in the incidence of dental caries between the case and control groups [23].

After one year, the children’s oral health status was compared between the control and intervention groups using the OHI-S index. In this regard, the findings of the present study showed a significant improvement in the oral health status of children in the intervention group in the one-year follow-up according to the OHI-S index. This finding was consistent with the results of a systematic review by Stein et al. in 2017 [22] that reported the impact of oral health education intervention on oral health. This meta-analysis found that the plaque index improved significantly based on the Loe and Silness index and O’Leary index following short-term educational interventions.

A recent review of Gargano et al., in 2019 advocated the involvement of parents in oral health programs in addition to stakeholders from different levels [24]. This is because children spend much time at home and therefore the active role of parents is important. In the present study, the oral health promotion program was effective in preventing caries progression in deciduous molar teeth and improving oral hygiene. This finding was in line with the results of a review study by Cooper et al. in 2013 [5] showing a statistically significant reduction in the plaque score in the test group receiving behavioral intervention compared to the control group. In addition, similar findings in two studies by Peterson et al. [20] and Jaime et al. [23] that used the Loe and Silness index for periodontal evaluation. Similarly, local studies conducted Saied-Moallemi et al. in 2009 [25] and Babaei et al in 2010 [17] reported the effectiveness of a school-based intervention.

In the present study, a comprehensive package including education workshop and supervised toothbrushing delivered. Our intervention package was prepared according to the recommendations of the World Health Organization (WHO) [1] including a training session for parents (mothers) and teachers in the form of a face-to-face workshop and pamphlet in addition to a supervised toothbrushing session for children in the school setting. A package including a toothbrush and fluoridated toothpaste was also given to children free of charge. Our finding was in line with a study by Peterson et al. in 2015 that reported that an oral health promotion training program including supervised toothbrushing with fluoride toothpaste was effective in reducing the incidence of caries [20]. Supervised toothbrushing is considered as an effective oral health promotion program for schoolchildren [5, 21]. However, a systematic review by Santos et al. in 2017 offered no conclusive recommendations regarding the effectiveness of supervised toothbrushing in the incidence of caries [26].

In the present study, both children and their parents were targeted for the oral health promotion program. According to the literature, the programs targeting children, parents, and teachers at the same time are more promising. This finding is consistent with a review study by Cooper et al. in 2013 that found that these interventions had a positive effect on maintaining oral health in children aged 4 to 12 years [5]. Similar to the studies conducted by Peterson et al. in 2015 [20] and Tai et al. in 2009 [21]. In this regard, Yekaninejad et al. conducted a local study in public elementary schools in 2012 and found that interventions targeting parents and school teachers in addition to children had more favorable results in promoting the children’s oral health [27].

After one year, the mean score of the parents’ oral health related knowledge, attitude and self-reported behavior was assessed in both groups. Although the parents’ attitude and the children’s behavior change were marginally significant in the intervention group, the difference was not significant. In this regard, the GEE analysis showed that the improvement of the parent’s attitude and children’s behaviors was marginally significant in the intervention group. In the present study, similar to a study by Gholami et al. [28], the GEE analysis was used to assess the impact of time and intervention considering the random sample effect to compare the intervention and control groups.

Conclusions

Our study was conducted to evaluate the long-term impact of an oral health promotion intervention program including supervised toothbrushing and parents’ education on the oral health status of schoolchildren aged 6–7 years old. The children in the intervention group had less caries in deciduous molar teeth and a better oral hygiene status compared to children in the control group. In the intervention group, the changes in the parents’ attitude and the children’s behavior were marginally significant. The oral health related knowledge and self-reported behavior of parents in the intervention group did not improve significantly.

Supporting information

Acknowledgments

We appreciate the school managers and instructors that participated in the study.