Fluoride toothpaste is the most widely used and rigorously evaluated fluoride treatment. Its introduction is considered the main reason for the decline in tooth decay in industrialized countries, and toothpaste appears to be the single common factor in countries where tooth decay has declined. Toothpaste is the only realistic fluoride strategy in many low-income countries, where lack of infrastructure renders water or salt fluoridation infeasible. It relies on individual and family behavior, and its use is less likely among lower economic classes; in low-income countries it is unaffordable for the poor. Fluoride toothpaste prevents about 25% of cavities in young permanent teeth, and its effectiveness is improved if higher concentrations of fluoride are used, or if the toothbrushing is supervised. Fluoride mouthwash and gel are about as effective as fluoride toothpaste; fluoride varnish prevents about 45% of cavities. By comparison, brushing with a nonfluoride toothpaste has little effect on cavities.