1. Design, setting and sampling
This cross-sectional analytical study conducted in Minia City, Upper Egypt between September 2016 and April 2019. The number of children participating in the study calculated on the basis of the following formula ; N = (Zα/2)2 s2/d2, where (N) is the number of participants and (d) is the degree of precision adjusted at 0.05. A pilot study conducted before launching the procedures on 56 children aged from 12 to 14 years and the standard deviation (s) of DMFT was 0.92. The total sample size was 1020 children after addin 10% to compensate the drop-off. After obtaining the necessary permissions from the Ministry of Education, the sampling process has been launched. The type of sample adopted in this study was a multistage stratified random sample. The selected strata based on gender (males and females), school type (public, private and international) and finally the school district (North, South, East and West). Details of sampling procedures illustrated in Fig. 1.
2. Eligibility criteria
Children aged from 11 to 14 years should fulfill the following criteria; (1) No orthodontic treatment or malocclusion or severe gingival or periodontal diseases. (2) Absence of any systemic, emotional or intellectual disabilities. (3) No emergency dental recall in the last three months reference
3. Study variables
An anonymous questionnaire used in this study which was divided into 2 principal sections; the first section included the following variables; (1) demographic data; (a) gender and (b) age, (2) socioeconomic data (a) mother’s level of education; dichotomized according to the number of education years into ≥ 9 years (greater than secondary and secondary school) and ˂ 9 years (less than secondary school or illiterate), (b) school type; classified into public and private schools, (c) household expenditures which recorded according to the cut-off poverty line in Egypt which is 3.20 US$ per day and [11, 12], (3) dental self-care and use of dental services; (a) frequency of tooth brushing, (b) frequency of mouth rinse use. The response of both ‘a’ and ‘b’ dichotomized into regular use (frequency is ≥ 1 time per day) and irregular (no tooth brushing or mouth wash use or ≤ 3 times per week), (c) use of dental floss, (d) frequency of dental visits per year for regular check-up. The response of ‘c’ and ‘d’ dichotomized into (yes or no). (5) clinical oral examination and recording dental caries status through recording the decayed, missing, filled teeth (DMFT) index for permanent teeth according to data into (≤ 3 and ˃ 3) based on the global target of score three announced by World health organization (WHO) for the year 2000 . Untreated carious cavity scores “i.e. Decayed tooth (DT) index” dichotomized into 0 and ≥ 1. The second section concerned with evaluating the OHRQoL using a previously validated Arabic version of CPQ11 − 14 short-form including 4 domains to assess oral symptoms (OS), functional limitation (FL), emotional well-being (EW) and social well-being (SW) and one self-perception question reported by each participant about his/her OHRQoL evaluation [8, 14].
4. Calibration, pilot study, and data collection
Firstly, two dentists with at least two years of residency at the Pediatric and Dental Public Health Department, Faculty of Dentistry, Minia University, trained for two weeks for calibration. The second step was conducting a pilot study on 67 children. The pilot study aimed to determine QoL mean and standard deviation required for sample size calculation and to test the intraexaminer and inter-examiner reliability. The results of the pilot study did not include in the final statistical analysis. Dental caries examination performed at two appointments with one-week interval. The clinical examination carried out using a visual-tactile method using a dental mirror and WHO probe five seconds per dental surface under artificial light use [15, 16].
5. Statistical methods
A Statistical Program Statistical Package for the Social Sciences (SPSS) version 20 has been used for statistical analysis. Data normality was examined and descriptive analysis including frequency tables, chi-square test for categorical variables, Independent-Samples T-Test and one-way analysis of variance (ANOVA) to compare CPQ11 − 14 overall score means of independent predictors. The mean/standard deviation, and median/Interquartile range (IQR) of the CPQ11 − 14 different domains were calculated. Univariate Poisson regression analysis was performed to determine the associations between decayed teeth (i.e. outcome variable) and demographic, socioeconomic, dental care and oral health related quality of life self-perception independent predictors. Predictors with a significant level exceeding 0.2 (p ˃ 0.2) were excluded from the final adjusted multivariate regression model. A conceptual model was released according to a hierarchy approach of determinants and risk factors and it was structured according to the model made by Paula et al. as shown in Fig. 2 . Predictors categorized into four models; Model 1 included gender, Model 2 incorporated model 1 plus socioeconomic variables Model 3 contained Model 2 plus child’s dental care and Model 4 implicated model 3 plus child’s oral health-related quality of life self-perception.
To declare the association between independent variables and QoL, a step-by-step, multivariate regression analysis was performed. The best fit defined by the highest R2). The level of significance was 5% (p-value ˂ 0.05) and 95% confidence interval (95% CI).