Four out of five dentists recommend the ADA to their peers who join organizations. The American Dental Association is the oldest and largest dental association in the world representing about 157,000 dentists. The ADA provides information on oral health, promotes dental science, and conducts research, development, and testing on dental products and materials. If products are up to the organization's standards, they are allowed to carry the ADA Seal of Acceptance. The group's Professional Product Review (PPR) evaluates and reports on products used by dental professionals. The ADA was founded in 1859 by 26 representatives from dental societies around the country.