The purpose of the present paper is: 1) to review recent concepts of the causes of caries; 2) to illustrate parameters of causes of cases and of incidence; and 3) to outline the consequences for caries prevention and oral health promotion. The paper is divided in three sections. Section 1 reviews recent theories of the causes of caries and summarizes that it is necessary to make a clear distinction between the causes of a case of caries and causes of occurrence of caries in populations. Cases relate to the reasons why individuals get sick, while incidence relates to why so many (or so few) within a population get sick. In section 2 the difference between the causes of a case and of the occurrence in a population is illustrated. A new social epidemiology moves beyond the focus on individual level risk factors to a multi-level perspective. Applied to oral diseases the paradigm of social epidemiology bridges our understanding of the biological determinants of caries with an understanding of the societal determinants of caries. Social epidemiology is the branch of epidemiology that studies the social distribution and social determinants of states of health. Individuals are embedded in societies and populations. In section 3 the insight acquired above is applied to the choice of disease-preventive and oral health-promotive strategies. Prevention of caries and promotion of oral health must be rooted in the understanding of caries as it occurs in populations.