Diseases of the dentition, such as dental caries and enamel malformations, are among the most common chronic illnesses worldwide. Caries generally cause oral discomfort and pain and infuence a child’s ability to eat, do schoolwork and sleep. The prevalence of caries in children in the Netherlands, as in other developed countries, has declined since 1975. Although it had stabilised, the prevalence of caries is now slightly increasing. Paediatric dentists warned about the increasing number of children who need extensive dental treatment, which received renewed attention, even in the national newspapers, in 2011. Because the incidence of caries has been declining, the emphasis of research has been more on predicting caries and other dental problems, such as developmental enamel defects. Developmental enamel defects are not uncommon, both in the primary and permanent dentitions, and can be divided into hypomineralisation and hypoplasia. Enamel hypoplasia is a quantitative defect of the enamel, and enamel hypomineralisation is a qualitative defect of the enamel identifed visually as an alteration in the translucency of the enamel, with a clear border, variable in degree, and a white, yellow or brown colour. It has also been termed a demarcated opacity. The first permanent molars with hypomineralisations are often associated with afected permanent upper incisors and, more rarely, lower incisors. Therefore, the name Molar Incisor Hypomineralisation (MIH) is currently used. In the primary dentition, hypomineralisations are also found in the second primary molars, a process known as Deciduous Molar Hypomineralisation (DMH).

The overall aim of this thesis was to describe and provide more insight into Deciduous Molar Hypomineralisation (DMH), including its prevalence, enamel mineral content, pre-, peri- and postnatal determinants and associations with Molar Incisor Hypomineralisation (MIH) and caries.