Differential diagnosis of molar incisor hypomineralisation and hypomineralised second primary molars: a scoping review

BACKGROUND: Molar Incisor Hypomineralisation (MIH) and Hypomineralised Second Primary Molars (HSPM) have been extensively studied; however the specific diagnostic boundaries distinguishing them from other developmental enamel defects remain unclear. OBJECTIVES: This review aims to systematically map the literature describing clinical, radiological, histological or structural features and patient-reported symptoms useful for the differential diagnosis of MIH and HSPM, and additionally to identify knowledge gaps for future research. METHODS: Primary studies addressing the differential diagnosis of developmental defects of enamel published in the period 1985-2025, written in English and involving human subjects were considered for inclusion in this scoping review. PubMed/MEDLINE, EMBASE, Cochrane Library and Scopus were searched. Two reviewers screened retrieved papers independently for eligibility and charted the data. The protocol was registered with the Open Science Framework registration number 10.17605/OSF.IO/P9UKD. RESULTS: A total of 23 reports were included in the review. More than half of the studies were case series (39.1%) and case reports (17.4%), including small samples (in 50.0% of the studies the sample size was fewer than 10 subjects). Amelogenesis Imperfecta (AI) was found in most papers (65.2%); other conditions included dental fluorosis, white spot lesions, and developmental defects associated with cleft lip and palate, antineoplastic therapy, syphilis, Turner syndrome and vitamin D-dependent rickets type 1. No single study directly compared MIH and HSPM with other enamel developmental defects in a controlled manner, representing a major limitation in establishing evidence-based differential diagnostic criteria. CONCLUSIONS: Future studies should include well-designed comparative analyses using standardized diagnostic criteria and objective measures in larger and more diverse patient samples.