School academic climate and oral health (tooth loss) in adolescents

Four trained and calibrated dentists performed oral examinations on the students, accord- ing to the methods and criteria recommended by the WHO [34]. Dental caries (DMFT index), presence of tooth and, periodontal condition (Community Periodontal Index-CPI) were eval- uated. Inter-rater reliability between examiners was satisfactory for dental caries and peri- odontal condition, with kappas ranging from 0.82 to 0.91 and, from 0.76 to 0.85, respectively. Tooth loss was our dependent variable, defined based on the absence of first permanent molars due to dental caries through the missing component of the DMFT score or due to other reasons. The survey inquired about sociodemographic characteristics and health behaviors adapted from the U.S. Youth Risk Behavior Survey questionnaire [35]. The questionnaire also included the Dental Anxiety Question (DAQ) [36] and the Self-perception of oral health status that was assessed through a single question (How would you describe your oral health?) with a 5-point Likert scale. Sociodemographic variables included gender, age, mother‘s schooling and receipt of family allowance (a social safety net in Brazil for poor families (per-capita monthly below $170 BRL/~$45 USD) and extremely poor families (per-capita monthly below $85 BRL/~$23 USD). Our contextual variables included the school rate of participation in the National High School Examination (ENEM) using the mean of the rate in 2016 and 2017 available in public database. Z-scores were used to standardize the variance in rate of participation. The type of

school was also assessed (regular vs. full-time/partial full-time). In Brazil, most schools operate 4 hours a day, but a few schools run full-time, i.e. 8 hours per day. The Social Vulnerability Index (SVI) is a measure of neighborhood disadvantage made up of 16 indicators in three domains: urban infrastructure, human capital and, income/labor. The SVI is available for each Human Development Unit (HDU) that is the smallest socioeconomi- cally homogeneous area unit in a city. We obtained the SVI and boundaries for each HDU in the city of Olinda from the Brazilian Institute of Geography and Statistics’ 2010 Demographic Census [37]. Data analysis was carried out using STATA/IC version 15.1. Bivariate analysis was con- ducted using Pearson’s chi-squared test and T-tests for categorical and numerical variables, respectively. Tooth loss (count variable) was the outcome in the multilevel Poisson regression (with random intercept). The individual variables included sociodemographic characteristics (age, sex, mother’s level of schooling, receiving a family allowance–proxy of poverty), clinical variables (decayed teeth–DMFT�1, and teeth affected by periodontal disease—CPI�3), and subjective ratings (self-perception of oral health and dental anxiety). We ran a sequence of multilevel models. The first model included only the dependent vari- able–i.e., the empty model (Model 1). The second and third models included the contextual variables (Model 2) and individual variables (Model 3), respectively. Next, we added the indi-

vidual and contextual variables together (Model 4). We used the proportional change in vari- ance (PCV) to assess changes in the random intercept term. According to Merlo et al. [38] the PCV represents the proportional change in the area level variance compared to the empty model (Model 1). We also used the Median Rate Ratio (MRR) in accordance to Austin et al. [39] to assess the reduction of the heterogeneity in each sequence of models. When the MRR equals 1.0, it means that there is no heterogeneity between the contexts analyzed. We tested the fitted multilevel Poisson regression model using the 2 Res log-likelihood. Results A total of 2,500 students completed the questionnaires out of the 2,700 adolescents (and parents) who consented to participate in this study (92.6% rate response). The response rates PLOS ONE School academic climate and tooth loss in adolescents PLOS ONE | https://doi.org/10.1371/journal.pone.0233505 May 21, 2020 4 / 11