The oral health promotion program was a composite intervention with both group and individual components. The group intervention consisted of:

1. Group oral health education 2. Display of Bass tooth-brushing methods 3. Broadcasting of songs as tooth-brushing reminders; The individual interventions included:

1. Instruction in the Bass tooth-brushing method 2. Individual behavioral modification method

The group intervention consisted of:

1. Group oral health education 2. Display of Bass tooth-brushing methods 3. Broadcasting of songs as tooth-brushing reminders; The individual interventions included:

1. Instruction in the Bass tooth-brushing method, 2. Individual behavioral modification method

Plaque Control Index (PCI) developed by O'Leary et al. to score the primary outcome, plaque accumulation, on the surfaces of the teeth. The score was computed by the existence of plaque divided by all examined surfaces; a higher plaque index indicated poor oral hygiene. We calculated a person-level plaque score by averaging plaque scores for all teeth at each examination.