**1. Introduction**

Several epidemiological studies (Okawa, et al., 1992; Marthaler & O'Mullane, 1996; Beltrán-Aguilar, et al. 1999; Vrbič, 1996; Brown, et al., 2000; Carvalho, et al., 2001; Estupiñan-Day, et al., 2001; Bönecker, et al., 2003) on dental caries experience in children and adolescents have been carried out around the world for the last three decades. Most of the reports agree that caries has been reduced, and these data have been confirmed by the Global Data Bank of the World Health Organization; however, the distribution and severity of dental caries varies in different parts of the world and within the same region or country.

Caries decline has been observed in children and adolescents from industrialized countries while those living in some less developed countries show a tending to increase. The reported caries reduction is the result of a number of public health measures, coupled with changing living conditions, lifestyles and improved self-care practices. (Petersen, et al., 2005)

It has been shown that schools provide an important setting for promoting health. (Kwan, et al., 2005) In Mexico, a school-based caries preventive program was established in the 1970's in the State of Mexico as a pioneer program. This program is focused on oral health education and mouth rinse (0.2% NaF) twice a month; however, there are no previous reports that assess the impact of this local program on dental caries prevention. It is assumed that caries will be reduced.

The aim of this study was to evaluate annually the impact of a school-based caries preventive program on the dental status and caries incidence, in Mexican schoolchildren within a three year period.
