Which of the following is the most important preventive therapy for an 8 year old living in a non-fluoridated community, with closed contacts in the posterior quadrants and disto-occlusal restorations on all primary first molars?

Twice daily brushing with fluoride toothpaste.

Weekly 0.2% NaF rinse.

Fluoride varnish at 1 month intervals.

Daily sodium bicarbonate rinse.