Massignan C, et al. - In this school-based cross-sectional study, researchers determined the prevalence of probable sleep bruxism (SB) in the primary and mixed dentitions using non-instrumental approach, and assessed if there was a link between sleep quality and probable SB in different age ranges. Participants were children aged 2–5 (primary dentition, n = 372) and 8–10 years old (mixed dentition, n = 563) enrolled in public schools at Florianopolis and their parents. By means of questionnaires, information on sleep characteristics, socioeconomic status, and presence of probable SB was obtained and evaluated. Evaluations for tooth wear were also performed by 7 trained examiners (Kappa > 0.7). With probable SB as a dependent variable, unadjusted and adjusted Poisson regression was carried out. Findings revealed a higher (32.7%) prevalence of probable SB in mixed than in primary dentition (22.3%). In children aged 8–10 years, a link was observed between poor sleep quality and probable SB. In both dentitions, no associations were seen between probable SB and sex, socioeconomic, head of the household educational status, drooling, and tooth wear.