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SUBJECTS AND METHODS
This study followed the ethical guidelines laid out for studies conducted at the Dental School, National University of Mexico and the Autonomous University of the State of Hidalgo. This analysis is part of a larger project that measured diverse oral health indicators (Methods and results for dental caries dental fluorosis tooth loss and health services utilization have been previously published).
Statistical analysis
An indicator of socioeconomic position (SEP) was constructed using occupation of both parents. These variables were combined using principal component analysis polychoric correlation (18). The first component explained 59.8% of the variability and was divided in tertiles, with the third tertile representing the highest SEP. Given that some mother and father information was missing, data were imputed using imputation by regression. Statistical analysis consisted of determining the percentages and frequencies throughout the variable categories. Admittedly limited, this analytic approach was purposefully chosen because the use of composite indicators precluded a more detailed, individual-level analysis. They are population-level indicators; examples in oral epidemiology have been used beforehand, such as the Fluorosis Community Index or the Significant Caries Index .
More than half (51.8%) had health insurance coverage with either one of the two largest, employment-related third-party funded health plans in Mexico: IMSS (Mexican Institute of Social Security) or ISSSTE [Institute of Security and Social Services for State Workers] (both publicly funded, with plan-defined contributions from employers and employees). Only 14.0% had some type of private health insurance. About one-third of the population had no health insurance. Only 15.0% reported having had a dental visit in the year before the study. Most mothers (94.8%) indicated they could read and write but half of the mothers (50.7%) had only six years of schooling or fewer; about the same proportion pertained to fathers (49.7%). In terms of family structure, it was found that only 5.6% of adolescents lived with one parent, either father or mother.