In an effort to promote adequate development of the masticatory system and prevent dental diseases, the Oral Health Promotion Project (OHPP), which focuses on diet, was started in 1984. The intervention was carried out over eight years and then followed up for a further nine years, in a district with no regular dental service, on Miyako Island, Okinawa, Japan. The aims of this study were to evaluate the project's effect on dental caries and masticatory function.