Effects of Educational Interventions on Oral Hygiene: A Systematic Review and Meta-Analysis

Background: The objective of this study is to evaluate the effects of school based oral health and meta-analysis. Methods: Our investigation was conducted in electronic databases including MEDLINE Ovid), Embase Ovid, Scopus), Web of Science from 2000 to march 2018.The data were extracted based on a standard data collection form specific to observational studies, and entered into RevMan 2014. Inclusion criteria included individually randomized controlled trials (RCTs) or cluster-RCTs including quasi- experimental studies that were related to oral health interventions. Software RevMan 2014was used for meta-analysis. A meta-analysis was carried out using random-effects models. Results: Twelve studies of students in this review finally entered the study including five individual RCTs, four cluster-RCTs, and three quasi-experimental studies. The intervention study period ranged from 1 month to 9 month. Interventions described in the studies briefly included oral health education with activities such as lectures, albums, slides, pamphlets, posters, and role playing. Meta-analyses showed a significant difference in knowledge (SMD 3.31, 95% CI 2.52 to 4.11; I 2 = 98; P < 0.001), attitude (SMD 1.99, 95% CI 0. 43 to 3.54; I 2 = 99; P < 0.001), behavior (SMD 4.74, 95% CI 3.70 to 5.77; I 2 = 99; P < 0.001), plaque index (SMD -1.01, 95% CI -1.50 to -0. 51; I 2 = 97; P < 0.001) and Gingival index (SMD 0. 33, 95% CI -0. 36 to 1. 02; I 2 = 98; P = 0.34) for students receiving educational interventions compared to those receiving usual care . Discussion: The systematic review concludes that educational interventions are effective for improving oral health knowledge, attitudes, behaviors, etc., which could potentially lead to improved oral health, reduced oral diseases, and reduced costs from treating oral diseases.


Introduction
Oral health is a basic component of public health and well-being [1][2][3]. Poor OH such as dental caries, periodontal disorders and missing tooth are important public health issues around the world given the fact that poor oral hygiene has wide-spreading impacts on overall health and quality of life. Some common diseases include tooth decay (cavities), gum (periodontal) disease, and oral cancer are caused from the direct effect of untreated OH problems [4]. There is a link between poor OH and social-behavioral and environmental factors possibly leading to poor nutrition, absence from work and school, pain and suffering, and increased healthcare costs [5,6] . According to the Global Burden of Disease Study (2016), at least 3.58 billion people are afflicted with oral diseases at a global scale. In fact, caries of the permanent teeth has been the most common of all the target conditions. The global estimation is that 2.4 billion people are faced with caries of permanent teeth and 486 million children are afflicted with caries of primary teeth [7].
Tooth decay is common in about 50 % of the world's population [8]. The World Health Organization reported in 2015 that most of the adults and schoolchildren experience dental caries and 5%-15% of most populations are affected by severe periodontitis [9].
OH can be improved if certain challenges are overcome. Especially in developing countries these challenges are harsher. Thus, it is essential to improve public health programs globally and to take effective preventive measures against diseases and at the same time to promote OH [10].
OHE programs continue to be promoted and practiced in schools, which implies that the critical evaluation and summarization of that evidence is key to give clinicians, stakeholders and decisionmakers the required information about the cost-effectiveness of OH programs which are educational in type [11].
Considering the low cost of these interventions compared to the treatment of oral diseases, it is crucial for public health managers, especially in developing countries, to conduct evidence-based effective preventive measures against diseases while promoting OH [10,12,13].
The past decades have witnessed a growing interest in the effectiveness of oral/dental health interventions. Thus, achieving a sound understanding of these studies and examining their effectiveness require systematic reviews. Though there has been systematic reviews with this concern, each has addressed one aspect of the topic of interest [6,14,15]. Yet, the present study aims to explore the effectiveness of oral/dental health-related interventions in a particular student population considering all variables with short-term consequences such as awareness, attitude, behaviors such as brushing teeth, flossing and so on as well as long-term consequences such as tooth plaque and gums bleeding. The aim of this study is to evaluate the effects of school based OH interventions programs on students' oral hygiene, in developing countries.

Search methods to select the studies
This systematic review was based on the search strategy developed for MEDLINE Ovid and Embase (Pico), Scopus and Web of Science. The search strategy used a combination of controlled keywords and free-text terms include: ("Student" OR "School Student" OR "Primary school" OR "Secondary school") AND ("Training" OR "Education" OR "Intervention" OR "Program" OR "Health education" OR "Health promotion" OR "Text message" OR "peer education" OR "distance learning" OR "distance education" OR "EHealth") AND ("Dental Health" OR "Oral health" OR "Brushing" OR "Flossing" OR "Dental plaque" OR "DMFT" OR "Oral hygiene" OR "Dental Hygiene" OR "tooth" OR "teeth" OR "Gingival") AND ("Knowledge" OR "attitude" OR "Behavior" OR "Performance" OR "belief" OR "skill" OR "practice").
In addition, search engines such as Google and Google Scholar were also used to identify all potentially eligible publications. We also scanned reference lists of relevant papers to identify additional papers (snowballing).When searching the electronic databases, authors placed English and Persian language of publication.

Inclusion criteria
Individually randomized controlled trials (RCTs) or cluster-RCTs including quasi-experimental studies were used to enhance oral hygiene (dental plaque), associated knowledge, and attitude, performance of students using one or more school-based OHE and/or oral health promotion interventions programs (the case group in comparison with consistent oral hygiene education (the control group). The studies mentioned above must also have been in line with the Pico conditions: Population: Studies that have evaluated the primary, middle, and high schools in their communities; Indeed, Male and female students at primary and secondary schools were selected for this study.
Most of them were 6-18 years old.
Intervention: School-based educational interventions to improve scores on OH variables including knowledge, attitude, behavior, gingivitis, dental plaque and DMFT.
Comparison: Studies with groups that got any sort of OHE intervention vs controls (the group had not received any training).
Outcome: Studies that assess scores on OH variables including knowledge, attitude, and behaviors such as brushing and flossing that determined by any tools applied in the included studies (e.g. questionnaire or interview), gingivitis, dental plaque and DMFT. It is noteworthy that gingival index measured by gingival scores, Dental plaque measured by plaque scores and DMFT scores (The score of decayed, Missing and filled teeth).

Screening, Data extraction
The search strategy was conducted by two of the review authors (ASM, SD). The first phase was a search in the titles and abstracts and done independently reviewed by two authors. The second phase was marked by a thorough checking through the articles in full-text by both authors independently.
The review authors were not blinded to authors of included studies. If disagreement occurred, the two review authors would try to solve it through discussion; otherwise, they would seek consultation with a third review author and finally those articles that were mutually agreed-upon were selected for inclusion. The collected data included author's name, publication year, country, sample size, frequency for each group, participants, age range, effects, delivery type, language, study design, details of the intervention, outcome measures, and follow-up. Data extraction was done independently by two review authors (AS, SD) by applying a standard survey data collection, which was put into Review Manager 5 Software (RevMan 2014). The extracted data were entered in Excel software 2010 in accordance with the above-mentioned categories. Data was extracted based on the fidelity of the intervention implementation. If, information on the afore-mentioned issues was insufficient, authors gathered additional information through contacting authors of the primary studies. The Cochrane Collaboration tool was applied to evaluate the risk of bias. The risk of bias was assessed in seven specific domains: random sequence generation; allocation concealment; blinding of participants and personal; blinding of outcome assessment; incomplete outcome data; selective reporting and other bias. This was done through the assignment to "low risk of bias," "high risk of bias" or "unclear risk of bias" rulings [16].

Statistical analysis
We used RevMan 2014 for meta-analysis. Before combined analysis, we assessed data heterogeneity among studies. Heterogeneity was evaluated statistically by the authors; it was also quantified among studies included in each analysis using the I² statistic. To assess the change of variables, mean difference (MD) was applied and its matching 95% confidence interval (CI) was used if the same tool was used. Moreover, if the used tools were not similar, the standardized mean difference was used (SMD). Measures for continuous data were evaluated as follows: mean change in Plaque Index (pre-and post-intervention phases) and standard deviations; mean change in gingivitis (pre-and post-intervention) and standard deviations.

Results
Results of the search Based on search strategies carried out by two (ASM, SD) screened 309 abstracts for inclusion, and assessed 37 publications in full text. Finally, 12 Studies had the eligibility criteria. Studies in English and Persian were included in the study. Excluded studies We excluded 25 studies: fifteen had no educational component; six included university students; and four assessed no predefined outcomes ( Figure 1). Duration of follow-up Follow-up for two studies was one month [17,18], and for six studies ranged from one month to three months [19][20][21][22][23][24]; for two studies was from three months to six months [25,26], and a study was followed up after nine months [27]. In one study, follow-up time was not reported. Altering knowledge, attitude and behavioral skills can be influenced by short-term educational interventions while changes in goal-oriented behaviors are supported by policies and environments [28]. Thus, within a short time span, mange changes can be made to oral/dental healthrelated knowledge, knowledge of different oral, oral cavity and material use, attitude, use of tooth brush and floss, visiting a dentist, behavior (alcohol consumption, cigarettes, fluoride toothpaste, delayed brushing of teeth, brushing of teeth with parents). Moreover, long-term effects such as tooth plaque, bleeding gum would take longer time. Post-intervention follow-up has been also considered as a key factor in categorizing the related body of research. It is also noteworthy that in several studies, short-term and long-term variables were taken into account. In such studies, the variable that related to the main consequence was considered. Authors categorized studies covering less than three months as short term and more than three months as long term (Supplement 2). Some interventions were complex interventions, which involved more than one active component. All educational interventions covered theoretical or practical education sessions, or both, on OH for students. The characteristics of the studies based on the variables studied are described in Table  1. The existing body of research explored the variety of educational content and methods. The interventions were described in oral/dental health pamphlets and instructions. The educational methods involved lecture, album, slides, films, pamphlets, booklets, dental educational models, PowerPoint presentations, role-play, use of tooth brush under the supervised tooth brushing system and group discussions. Moreover, teachers, peers and dentists were involved in the transfer of educational information (Table 2).  Statistical heterogeneity of studies was assessed through the calculation of tau 2 and I 2 . As the heterogeneity of studies s was higher than 25%, a random effects model was applied. Oral health-related knowledge Based on the results, ten studies reported oral health-related knowledge of students [17, 18, 20-23, 25,27,29]; all studies Oral health-related knowledge assessed by self-administered questionnaires. Data of twelve studies on students' knowledge were combined in the current study. Moreover, ten studies at high and unclear risk of bias including 2309 members of students were combined in a meta-analysis. Oral health knowledge scores improved significantly more among students receiving the oral health educational intervention compared with students that no receive educational activities (SMD 3.31, 95% CI 2.52 to 4.11; I 2 = 98; P < 0.001) (Figure 3). Oral health-related attitude Oral health-related attitude of students was evaluated by six studies [17, 18, 21, 23]. Selfadministered questionnaires were applied with Likert scale. Self-administered questionnaires were applied with Likert scale. Six studies including 1141 members of students were combined in a metaanalysis by the authors. Oral health attitude scores improved significantly more among students receiving the oral health educational intervention compared with students that no receive educational activities (SMD 1.99, 95% CI 0. 43 to 3.54; I 2 = 99; P < 0.001) (Figure 4). Oral health-related behavior Oral health-related behavior of students was evaluated by eight studies [17, 18, 21, 23, 25,27]. Eight studies including1909 members of students were combined in a meta-analysis by the authors. OH behavior scores improved significantly more among students receiving the oral health educational intervention compared with students that no receive educational activities (SMD 4.74, 95% CI 3.70 to 5.77; I 2 = 99; P < 0.001) ( Figure 5). Dental plaque index We meta-analyzed six studies [19-22, [24][25][26][27] and involving 1947 students. Dental plaque scores improved significantly more among students receiving the oral health educational intervention compared with students that no receive educational activities (SMD -1.01, 95% CI -1.50 to -0. 51; I 2 = 97; P < 0.001) ( Figure 6). Gingival index Authors meta-analyzed four studies [19,24,26,27] and involving 1541 students. Gingival scores improved significantly more among students receiving the oral health educational intervention compared with students that no receive educational activities (SMD 0. 33, 95% CI -0. 36 to 1. 02; I 2 = 98; P = 0.34) (Figure 7).

Discussion
Oral health knowledge scores improved significantly more among students receiving the oral health educational intervention compared with students that no receive educational activities. Therefore the effectiveness of OHE-related program has been able to increase of knowledge. According to the results by Kay and Locker, it was possible to enhance knowledge by dental health education [30]. The results of meta-analysis show that oral health attitude scores improved significantly more among students receiving the oral health educational intervention compared with students no receive educational activities. The results of the meta-analysis indicated that the educational program in the intervention group were able to improve the students' positive attitude towards health behaviors.
Effective education and raising knowledge can be one of the reasons for positive attitudes among students. On the other hand, improving attitude can lead to health behavior. Studies have shown that there is a positive relationship between positive attitude and frequent tooth brushing of students [38][39][40]. Moreover, the positive attitude of educational staff can lead to a positive attitude in students. A study showed that teachers who have a positive attitude towards oral hygiene of students can be a positive role model, and vice versa, teachers with a negative attitude would have an unfavorable effect on students' health behaviors [41]. According to the studies recommendations, the oral health knowledge, attitude, and behavior were improved by OHE based on theories and it is possible to use them to develop theoretical structure of the interventions [42][43][44][45]. Therefore the role of health education and health promotion in promoting OH can be crucial. In fact, educational interventions will be more effective when they are based on theories. Due to the insufficient of theory-based studies in this study, it was not possible to compare the efficacy of theory-based and routine interventions (without the use of theory).
The results of gingivitis outcome in meta-analysis showed that there was difference between the experimental and control groups indicating that OH intervention had effect on gingivitis reduction.
The results showed that majority of the studies had a short-term follow-up period. Therefore, there is a need to assess long-term studies, which can evaluate the effects of the education practices on those outcomes, especially because the goal of the education actions in the settings such as school is to prevent oral disorder and expand healthy behaviors and practices.
Dental plaque scores improved significantly more among students receiving the oral health educational intervention compared with students that no receive educational activities. These review showed the impact of OHE on plaque levels on short term. The systematic review of Prabhu and John showed that oral health educational interventions and consequently improvements in individuals' knowledge, attitude, and oral health-related practice were effective in improving OH indexes status such as reduction in dental plaque, gingival bleeding, and significant decline in dental caries [46]. Teachers are also trained in many countries and are used as a powerful tool for reducing dental plaque and improving oral hygiene among students (Petersen & Kwan, 2004). Therefore, health education and health promotion should be an essential element in educating teachers and other educational staff. Because the role of teachers in this field is very significant and valuable, they can affect thousands of students and families [37].
Most of the studies reported data on short-term effects (three or six months). Seemingly, follow-up period was sensible for outcome like plaque and gingivitis. Nonetheless, it should be emphasized that it was no adequate for other outcomes like knowledge and attitude. It is possible that constant impressions on knowledge and attitudes for school are required to pave the way for behavioral changes in OH care. Thus, outcomes should be measured in future studies in the longer term.
It is noteworthy that outside school in such contexts as hospitals, primary care centers and private dental clinics, there is also the possibility of making oral/dental health related interventions. However, schools might be the best place to promote oral/dental health as about a billion children worldwide spend most of their daily time at school [47]. Furthermore, such factors as reduced lost time, The present authors suggest that further investigations are done to make up for the present limitations. The first limitation was that this study was narrowed down to developing countries.

Conclusions
The systematic review concludes that educational interventions are effective for improving oral health knowledge, attitudes, behaviors, etc., which could potentially lead to improved OH, reduced oral diseases, and reduced costs from treating oral diseases.

Availability of data and materials
The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Consent for publication
Not applicable.

Competing interests
The authors have no conflicts of interest.

Funding
This study is sponsored by Shahid Beheshti University of Medical Sciences in Tehran. The funding agencies had no role in the design of study, data collection and analysis, or presentation of the results.

Authors' contributions
MGH, SD, and ASM designed the study. ASM, AA, MM and SD wrote the first draft. All authors contributed to writing, revising, and approved the final manuscript.  Comparison Educational intervention versus usual care, Outcome Oral health-related attitude.

Figure 5
Comparison Educational intervention versus usual care, Outcome Oral health-related behavior.

Figure 6
Comparison Educational intervention versus usual care, Outcome plaque index.

Figure 7
Comparison Educational intervention versus usual care, Outcome Gingival index.

Supplementary Files
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