Molar-incisor Hypomineralisation (MIH) is a tooth condition specifically affecting the enamel (outer layer of the tooth) of one or more of the child’s first adult molars (back teeth) and in some cases the incisors (front teeth). MIH affected teeth appear discoloured, and vary in presentation; cream, yellow or brown. Teeth are commonly very sensitive, painful and in severe cases crumbly. Furthermore, affected teeth often have a poor prognosis and are more susceptible to dental decay meaning the teeth are often extracted before adulthood. It is usually diagnosed when the adult molars and incisors erupt in the mouth at around 6-7 years of age. In some cases, it can also affect the primary teeth, which is known as hypominersalised second primary molars (HSPM) and is seen around 2-3 years of age.

MIH has a high prevalence; approximately 13.1% globally (95% CI 11.8-14.5%) and 15.9% in the UK (95% CI 14.5-17.1%). The literature suggests MIH is caused by disturbances during tooth development. This is influenced by genetics and environmental factors, particularly during pregnancy, time of birth and in the first few years of life. Some of the environmental factors investigated include breastfeeding, environmental toxins (dioxins and Bisphenol A), problems occurring at birth and childhood illnesses. However, the literature concludes that the aetiology of MIH is unclear. Currently, there is little research on maternal factors and MIH, particularly the common environmental risk factors; maternal smoking (7 studies – the most recent suggesting a significant association) and alcohol consumption (2 studies), both in which the strength of evidence is weak and conflicting. Furthermore, much of the research conducted is retrospective and therefore prone common biases such as recall bias. There is a need for high-quality prospective studies. Other studies suggest that maternal smoking and alcohol consumption are associated with offspring HSPM. The embryological development of the second primary molars and first permanent molars are similar, and therefore may share the same environmental influences.

We propose to conduct a prospective study looking at the association between common maternal pregnancy characteristics and MIH. These include maternal smoking, alcohol consumption and body mass index (BMI). We will assess for the presence of residual confounding by including a negative parental exposure control. This involves comparing the confounder adjusted associations of maternal pregnancy exposures with the offspring outcome of interest to similarly adjusted associations of the same characteristics (negative controls) in the father. Similarly, we will use offspring dental trauma as a negative control outcome. Triangulating results from conventional multivariable regression, negative exposure controls and negative outcome controls provides scope to improve causal understanding.