Possible sleep bruxism and hair cortisol in children: A birth cohort study

This study aimed to test for an association between hair cortisol, as an indicator of chronic stress, and possible sleep bruxism among children participating in the 2015 Pelotas Birth Cohort Study. Data from 3229 children were analysed. Possible sleep bruxism was identified based on caregivers' reports when the child was 4 years old. Trained fieldworkers collected hair samples from children, and a standardized protocol was used for hormone extraction and cortisol quantification from the hair. Information on socioeconomic, demographic, psychological and behavioural characteristics was gathered through questionnaires. Poisson regression with robust variance was used to evaluate the impact of hair cortisol concentration on the occurrence of possible sleep bruxism, guided by a directed acyclic graph. The prevalence of possible sleep bruxism was 21.46% (n = 693); median hair cortisol concentration was 7.8 pg mg^-1. Hair cortisol concentration was not found to be associated with the occurrence of sleep bruxism. However, the presence of sleep bruxism was linked to higher maternal education (p = 0.027), maternal stress level (p = 0.032), excessive use of electronic devices (p = 0.007), and child emotional and behavioural problems (p = 0.003). Furthermore, female sex was associated with a lower frequency of possible sleep bruxism (p = 0.003). There was no association between chronic stress, as measured by hair cortisol concentration, and the occurrence of possible sleep bruxism. This study underscores the role of sociodemographic factors and children's mental health in the occurrence of sleep bruxism among children in this population.