Residual factors associated with poor oral hygiene among Japanese kindergarten children: a cross-sectional study

OBJECTIVES: To identify behavioural and household factors associated with poor oral hygiene among Japanese kindergarten children in a population with high health awareness, using the Debris Index-Simplified (DI-S) as a clinical proxy for early oral hygiene deterioration. DESIGN: Cross-sectional study. SETTING: Seven kindergartens in Sapporo city, Japan. PARTICIPANTS: Of the 1229 kindergarten children invited, 871 provided parental consent (consent rate: 70.9%). Among them, 675 children aged 1-6 years who completed both the questionnaire and oral examination (completion rate: 54.9%). Most post-consent losses were due to logistical and staffing constraints. Children were stratified into ≤3 year and ≥4 year academic classes. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome was oral hygiene status based on the DI-S scores (categorised as good (DI-S=0) or poor (DI-S>0). The secondary outcome was the presence of dental caries, defined as decayed, missing and filled primary teeth: dmft≥1. Multivariable logistic regression was used to estimate associations between poor oral hygiene and behavioural and household factors. RESULTS: Among the 675 children, 168 children (24.9%) exhibited poor oral hygiene (DI-S>0) and 89 children (13.2%) had dental caries (dmft≥1). In multivariable analysis adjusted for demographic, dental and dietary variables, poor oral hygiene was significantly associated with being from a multiple-child household (OR 1.67, 95% CI 1.16 to 2.42) and irregular juice consumption (OR 1.60, 95% CI 1.07 to 2.38). Age-stratified analysis revealed that these associations persisted among those in the ≥4 year class, with additional significance for infrequent tooth brushing (