Screen Time, Juice Consumption, Caregiver-Assisted Toothbrushing and Dental Caries at Age 3 Years: A Population-Based Cohort Study in Japan.

OBJECTIVES: To examine whether screen time at age 3 years was associated with dentist-assessed dental caries, and whether regular juice consumption modified this association. METHODS: This population-based retrospective cohort used linked municipal child health records at 18 months and 3 years in Okinawa, Japan (2014-2019). The outcome was any dental caries at age 3 years. Exposures were caregiver-reported screen time (≤ 1, 1-2, > 2 h/day), regular juice consumption, caregiver-assisted toothbrushing and breastfeeding at 18 months. Adjusted risk ratios (aRRs) were estimated by modified Poisson regression, adjusting for demographic, household, sleep, dietary and routine factors and baseline caries. Effect modification by regular juice consumption was assessed on multiplicative and additive scales; multiple imputation addressed missing data. RESULTS: Among 60 404 children, 15 608 (25.8%) had caries at age 3 years; of 58 815 caries-free at 18 months, 14 269 (24.3%) developed it. Screen time > 2 h/day carried higher caries risk than ≤ 1 h/day (aRR 1.08; 95% CI 1.04-1.12). Regular juice consumption was strongly associated (aRR 1.32; 1.28-1.35), whereas caregiver-assisted toothbrushing was protective (0.66; 0.64-0.68). The association was modified by regular juice consumption: among non-consumers, aRRs were 1.07 (1.03-1.11) and 1.13 (1.08-1.18) for 1-2 and > 2 h/day, versus 0.98 and 1.00 among regular consumers; the joint association was sub-additive. Multiple-imputation analyses were similar. CONCLUSIONS: Higher screen time was modestly associated with caries, whereas regular juice consumption and absence of caregiver-assisted toothbrushing were major correlates; the screen-time association was most evident among children without regular juice consumption. Prevention may need to address screen-related routines alongside dietary and oral hygiene practices.