Systemic and Environmental Risk Factors Associated with Molar Incisor Hypomineralisation.

The etiology of molar incisor hypomineralisation (MIH) has been attributed to systemic and environmental factors since 2001. The identification of MIH etiology is fundamental to better understand this condition, for differential diagnosis, and to identify the patient group at risk of MIH. Although the etiology of MIH is still unclear, it is stated as a multifactorial origin, with an overlap of systemic and genetic risk factors. The aim of this chapter was to discuss the systemic and environmental factors associated with MIH according to scientific evidence in the literature, relating it to the basic knowledge of amelogenesis and tooth development chronology. In this chapter, amelogenesis is described and illustrated in detail. Some characteristics of the amelogenesis process could explain some clinical features of the developmental defect of enamel, especially MIH. The chronology of tooth development was also referred to as a characteristic for the occurrence of MIH. Finally, the literature about systemic and environmental risk factors was revised, and the prenatal, perinatal, and postnatal factors associated with MIH were discussed. During the prenatal period, maternal health status, including illnesses during pregnancy and maternal smoking, are the main investigated factors associated with MIH. Prematurity (<37 weeks), low birth weight, and cesarean delivery are the factors associated with MIH during the perinatal period. Moreover, postnatal factors, such as common childhood illnesses, respiratory disease, infections, and antibiotic use, have been associated with MIH. New longitudinal studies that consider the synergy between exposure to environmental factors and biological susceptibility are likely to provide a new understanding of the etiology of MIH.