Trial design and study participants
This was a randomized controlled concurrent parallel trial conducted from October 2017 to September 2018. In concurrent parallel trial comparisons are made between two randomly assigned groups with one group exposed to intervention. Children belonging to 12–15-year-old age group studying in grade 8 and 9 in public and private schools of Dharan sub-metropolitan city, Nepal were included in the study.
Dharan is a sub-metropolitan city in Sunsari district of province No.1, Nepal. The total area of the sub-metropolitan is 192.32 square kilometers. According to 2011 Census conducted by Central Bureau of Statistics (CBS), Dharan Sub-Metropolitan City had total population of 137,705 with 64,671 males and 73,034 females. There were only 106,424 people fully literate as of 2011 who were able to both read and write, while 2349 people were able to read but not write. According to Nepal Government records as of 2017, there were total 6,515 school children studying in grade 1 to 12 in Dharan Sub-Metropolitan City with 3128 (48.01%) of males and 3387 (51.99%) females. The shortest distance from capital city (Kathmandu) of Nepal to Dharan through road is 379 km which takes around 8 h and 35 min.
Ethical considerations and trial registration
Ethical approval for the study was obtained from the Institutional Review Committee, B.P.Koirala Institute of Health Sciences (BPKIHS), Dharan (Ref. No.: 292/074/075-IRC and Code No: IRC/1086/017). Approval was also obtained from Thesis Protocol Evaluation Committee of BPKIHS, Dharan (Ref. No.: Acd/978/074/075). The study was registered as a clinical trial (www.ctri.nic.in) in the Indian Council of Medical Research (ICMR)- National Institute of medical Statistics; the Clinical Trial Registry India identifier no. CTRI/2018/05/013985 (http://ctri.nic.in/Clinicaltrials/rmaindet.php?trialid=23651&EncHid=57035.73346&modid=1&compid=19). It was retrospectively registered on 05/21/2018. Official permission was obtained from the Dharan sub-metropolitan city and the concerned school authorities before commencing the study. A written informed consent was obtained from all parents of the study participants and verbal assent from each child.
Secondary schools providing co-education were included in this study. Co-education means school providing education to both boys and girls. Cooperative 12–15 years old school children studying in grade 8 and 9 whose parents gave their written informed consent were included in this study. Cooperative means those children who had provided the verbal assent and given permission for oral examination.
Children with any systemic disease, requiring any emergency dental treatment and with orthodontic appliances were excluded.
Total 18 public schools and 42 private schools of Dharan sub-metropolitan city met the inclusion criteria. After getting verbal permission from the principals of the schools, 4 public and 8 private schools (20% of total) were randomly selected using lottery method, by an assistant who was not participating in the field study. A randomization master list was prepared based on computer generated random numbers and each school was assigned to a group (Group 1, Group 2) by a biostatistician. Allocation concealment were done using opaque envelope methods.
Systematic random sampling was done to include the students from the schools in each study group. Number of students from type of schools (public or private) and each school was selected on the basis of population proportion ratio.
Coding was given as 1 and 2 to the 2 different groups. It was not revealed during the data entry time and analysis time. The two groups 1 and 2 were revealed as control and experimental respectively only after completing the analysis.
This study considered (95% CI) and 80% power to estimate the sample size. For this purpose, mean ± SD (gingival index) value of intervention group (2A) 0.78 ± 0.42 and mean ± SD value of control group (1B) 0.94 ± 0.3822 respectively were taken. Therefore, mean of control group (µ1) = 0.94, mean of intervention group (µ2) = 0.78 and average standard deviation of control and intervention group (ϭ) = 0.40 .Using following formula, Sample Size (n) = (2 ϭ2 (zα/2 + zβ/2)2)/(µ1 − µ2)2, the sample size was calculated as 98. Considering 20% attrition rate total sample size was increased to 120 in each group.
The questionnaire contained pretested standardized closed ended questions which were selected from previous researches [16,17,18] (Annexure 1). Face and content validity of the structured questionnaire was done by three subject experts. A 23-item questionnaire was translated and validated in Nepali language (local language) through standard back translation method. Test–retest was used to check the reliability and internal consistency of the questionnaire. Cronbach’s alpha value of 0.81 showed good internal consistency of the questionnaire.
Each of the 23 multiple choice questions had a single correct answer. All questions had a binary outcome which was coded as one for correct and zero for incorrect. Every correct answer in baseline, 3 and 6 months after intervention was scored as 1 and wrong answers were scored zero. An overall composite score was then created, by adding the individual scores on each question. The highest possible score for oral health knowledge was 11 for each individual. The highest possible score for oral health practices and attitude were 8 and 4 respectively. The highest possible overall score for oral hygiene KAP was 23. The mean score was then calculated for each group and then compared. The percentage change was calculated by subtracting the pre-test percentage from the post-test percentage [100 × (baseline mean score-6 months score)/baseline score].
Face to face interview of the participants were done by the single investigator (KS). Time taken for each interview was 4–5 min. Demographic variables included age, sex, grade, type of school (public or private) and socioeconomic status (SES). SES was calculated using Kuppuswamy scale and classified as per the modifications done in the year 2009  using current consumer price index for the year 2017. The current consumer price index was obtained online from Nepal Rastra Bank website (Nepal RB 2017) and the conversion factor was calculated (Conversion factor = consumer price index 2017 divided by consumer price index of 1976) . The computed conversion factor was 26.7 (114.8/4.3). For simplicity, SES was categorized into upper (26–29), middle (11–25) and lower (≤ 10) class.
Clinical oral examination was done according to WHO basic oral health surveys methods . A pilot study was conducted among 25 participants of similar school children with similar age, grade and socioeconomic status, who were not involved in the main study, for training and calibration of the examiner, feasibility assessment of the study and the reliability of questions.
All children were examined at their schools, lying on a bench with the examiner seated behind the subject’s head, under artificial light. Oral examination was carried out by using sterilized instruments including mouth mirror, WHO probe and disposable gloves. Oral examinations were done to record Turesky–Gilmore–Glickman modification of the Quigley-Hein plaque index , Gingival index  and Dentition status and treatment needs at baseline and 3rd and 6th months of the study period. DMFT were calculated from dentition status and treatment needs.
Duplicate examinations were performed among 25 participants during the study to test the intra-examiner reliability which was measured by interclass correlation coefficient (ICC).
Oral health education included topics like importance of teeth, type of dentition, brushing and flossing techniques and dental caries—its etiology, signs and symptoms, complications, preventive methods, the role of fluorides, plaque and calculus and its effect on gingival and periodontal health, diet and nutrition, importance of oral health to general health. OHE was first provided in one school which was not considered in the main study for the validation of the OHE materials. OHE was provided by KS and supervised by AS and TKB.OHE using tooth models and PowerPoint presentation was given to 12–15 children in a single session of 30 min in each follow up to the experimental group by KS.
No OHE was given to the control group. In the experimental group, reinforcement of OHE was done at the 3rd and 6th months. To avoid contamination, only one group (either control or experimental) was included from one school. After completion of study (after 6 months) the same OHE that was given to the experimental group was given to the control group. During first and second follow up time maximum 3 visits to every schools was done to include the maximum number of children. Those children who were not present during examination at follow up periods were considered as missing.
Evaluation of intervention
Baseline assessment was done in January–February 2018, second and third assessment was done in April–May and August 2018 respectively. On each visit oral health education was given as intervention for experimental group.
Intervention was evaluated by assessing the improvements in oral hygiene knowledge, practice and attitude (correct answers) and changes in plaque and gingival scores in experimental group compared with the control group.
The primary outcome measures were change in mean score of oral hygiene KAP, plaque control, gingival health and DMFT after intervention at 3 and 6 months in experimental and control group.
After completion of the trial, data obtained were entered in Microsoft Excel Sheet version 2007 and analyzed using the Statistical Package for Social Sciences (SPSS version 11.5). The level of significance was set at p ˂ 0.05. Intra-examiner reproducibility for coding was measured by intra-class correlation coefficient (ICC).
Descriptive analysis was performed to summarize the clinical and socio-demographic characteristics of each group at baseline in order to assess how comparable the groups were at beginning of the study. Descriptive statistics including the mean, median and standard deviations were computed for oral hygiene KAP, plaque index (PI), gingival index (GI) and DMFT.
Chi-square test was used to find the significance of study characteristics on categorical scale. Repeated-measures ANOVA was used to find the significance of oral hygiene knowledge, practice and attitude, plaque index and gingival index scores between two groups at baseline, 3 and 6 months respectively. For significant repeated measures ANOVA post hoc Tukey’s test was used. Independent t test was used to find the pairwise significance between the groups regarding oral hygiene KAP, plaque index and gingival index scores. Mann–Whitney u test was used to find the pairwise significance between 2 groups regarding mean DMFT.