Frequencies of enamel hypomineralisation in permanent and primary molars in a medieval and early-modern-age population (7th - 17th c.) in Sains-en-Gohelle (Pas de Calais, France).

Molar Incisor Hypomineralisation (MIH) is defined as a qualitative demarcated enamel hypomineralisation defect of tooth enamel affecting at least one first permanent molar (FPM), often affecting permanent incisors. More recently, the term Hypomineralised Second Primary Molar (HSPM) was used to describe similar defects affecting second primary molars. Our observational study aimed at determining HSPM and MIH frequencies in a medieval and early-modern-age population population (Sains-en-Gohelle, France, 7th - 17th centuries) and compare it to the current worldwide and French prevalence values. To date, there are no other studies on this subject in France. European studies have been published, but the diagnosis of these pathologies is based solely on a visual examination. Our study differs from others by using objective diagnostic. microtomography and X-ray fluorescence. The use of these diagnostic methods allows differentiation between hypomineralised and taphonomic lesions. The frequencies of MIH and HSPM were, respectively, 12.3% and 13.3%. In fact, there were 10 individuals with at least one first permanent molar affected by MIH amongst the 81 individuals with at least one first permanent molar present, and 15 individuals with at least one second primary molar affected by HSPM among the 113 individuals with at least one second primary molar present.The presence of MIH and HSPM in ancient populations with frequencies respectively equivalent and higher than current worldwide averages renews the debate and questioning about the aetiological factors of these pathologies.