Increasing Diagnosis of Enamel Hypomineralisation in a Sample of More Than 70 000 Children in the City of Zurich: Repeated Cross‐Sectional Prevalence Analyses and a Retrospective Longitudinal Cohort Analysis

BACKGROUND: The prevalence of molar-incisor hypomineralisation (MIH) has garnered increasing attention, with a likely association to hypomineralised second primary molars (HSPM). AIM: To elucidate the prevalence of MIH and its association with HSPM. DESIGN: This retrospective observational study combined repeated cross-sectional analyses with a retrospective longitudinal cohort analysis of over 70 000 children (851 685 observations) attending public schools in Zurich, Switzerland (2005-2019). Hypomineralised lesions in second primary and first permanent molars were assessed. Prevalence rates and sex differences were calculated using annual age-specific cross-sectional samples. Logistic and log-binomial regressions complemented by machine learning algorithms explored the longitudinal association between HSPM and MIH in children with records both at ages 5-7 and ≥ 8. RESULTS: HSPM prevalence in five-year-olds increased from 5% to 13% between 2005 and 2019. Hypomineralised permanent first molars in eight-year-olds increased from 12% to 21%. Children with HSPM were approximately twice as likely to develop hypomineralised permanent molars (OR = 2.3; 95% CI: 2.1-2.5; PR = 1.9; 95% CI: 1.7-2.0). CONCLUSION: This large dataset confirms increasing HSPM and MIH diagnosis in Zurich between 2005 and 2019 and supports HSPM as a useful clinical indicator for elevated MIH risk. Limitations include study retrospectivity and potential examiner variability.