Ekstrand KR, Christiansen MEC, Qvist V, Ismail A. Factors associated with inter-municipality differences in dental caries experience among Danish adolescents. An ecological study. Community Dent Oral Epidemiol 2009; 00: 000-000. (c) 2009 John Wiley & Sons A/SAbstract - Background: Caries on children and adolescents in Denmark has declined significantly over the last 30 years. Our first analysis in 1999, however, disclosed huge inter-municipality disparities in mean DMFS values as well as in prevalence of caries on Danish children; that fluoride in the water supply and the length of the education of the mothers could explain up to 45% of the above-mentioned disparity and that very few municipalities were positive outliers, i.e. were providing significant better caries results than expected from the background variables. Three of the aims of this second analysis were to repeat the analyses done on the 1999 sample, but now on a 2004 sample and then compare it with the results from 1999. A fourth aim was by means of an interview of CDOs to determine their interpretation of relevant conditions in the public dental health service in relation dental health outcome. Methods: A total of 204 (99%) and 191 (93%) municipalities were involved in 1999 and 2004, respectively. Unit of analysis were the municipalities. Mean DMFS of 15-year-olds was used as outcome variable. Eight background variables were accounted for during the analysis: For the fourth aim, a sample of CDOs representing municipalities with positive (n = 10), with no change (n = 10), or with negative change (n = 10) in mean DMFS, relative to all municipalities, between 1999 and 2004 was selected. Results: The inter-municipality variation in mean DMFS 1999 was 0.88 to 8.73 and in 2004 was 0.56 to 6.19. The analyses found that fluoride level of the drinking water and mothers' length of education were significant variables explaining about 44% of the variations in mean DMFS in both years. Only one municipality was characterized as a positive outlier in 1999 as well as in 2004. The dose-response relations between increasing fluoride concentrations in the water supply and DMF-S values diminished in both years at a level above 0.35 ppm. The structured interview disclosed that municipalities with significant improvement in mean DMFS from 1999 to 2004 had established goals and were committed to the prevention of dental caries at the individual level. Instability in manpower; number of children in the service and economy was associated to municipalities with negative changes in caries experience.